diff --git "a/venv/lib/python3.10/site-packages/scipy/stats/_continuous_distns.py" "b/venv/lib/python3.10/site-packages/scipy/stats/_continuous_distns.py" new file mode 100644--- /dev/null +++ "b/venv/lib/python3.10/site-packages/scipy/stats/_continuous_distns.py" @@ -0,0 +1,11933 @@ +# +# Author: Travis Oliphant 2002-2011 with contributions from +# SciPy Developers 2004-2011 +# +import warnings +from collections.abc import Iterable +from functools import wraps, cached_property +import ctypes + +import numpy as np +from numpy.polynomial import Polynomial +from scipy._lib.doccer import (extend_notes_in_docstring, + replace_notes_in_docstring, + inherit_docstring_from) +from scipy._lib._ccallback import LowLevelCallable +from scipy import optimize +from scipy import integrate +import scipy.special as sc + +import scipy.special._ufuncs as scu +from scipy._lib._util import _lazyselect, _lazywhere + +from . import _stats +from ._tukeylambda_stats import (tukeylambda_variance as _tlvar, + tukeylambda_kurtosis as _tlkurt) +from ._distn_infrastructure import ( + get_distribution_names, _kurtosis, + rv_continuous, _skew, _get_fixed_fit_value, _check_shape, _ShapeInfo) +from ._ksstats import kolmogn, kolmognp, kolmogni +from ._constants import (_XMIN, _LOGXMIN, _EULER, _ZETA3, _SQRT_PI, + _SQRT_2_OVER_PI, _LOG_SQRT_2_OVER_PI) +from ._censored_data import CensoredData +import scipy.stats._boost as _boost +from scipy.optimize import root_scalar +from scipy.stats._warnings_errors import FitError +import scipy.stats as stats + + +def _remove_optimizer_parameters(kwds): + """ + Remove the optimizer-related keyword arguments 'loc', 'scale' and + 'optimizer' from `kwds`. Then check that `kwds` is empty, and + raise `TypeError("Unknown arguments: %s." % kwds)` if it is not. + + This function is used in the fit method of distributions that override + the default method and do not use the default optimization code. + + `kwds` is modified in-place. + """ + kwds.pop('loc', None) + kwds.pop('scale', None) + kwds.pop('optimizer', None) + kwds.pop('method', None) + if kwds: + raise TypeError("Unknown arguments: %s." % kwds) + + +def _call_super_mom(fun): + # If fit method is overridden only for MLE and doesn't specify what to do + # if method == 'mm' or with censored data, this decorator calls the generic + # implementation. + @wraps(fun) + def wrapper(self, data, *args, **kwds): + method = kwds.get('method', 'mle').lower() + censored = isinstance(data, CensoredData) + if method == 'mm' or (censored and data.num_censored() > 0): + return super(type(self), self).fit(data, *args, **kwds) + else: + if censored: + # data is an instance of CensoredData, but actually holds + # no censored values, so replace it with the array of + # uncensored values. + data = data._uncensored + return fun(self, data, *args, **kwds) + + return wrapper + + +def _get_left_bracket(fun, rbrack, lbrack=None): + # find left bracket for `root_scalar`. A guess for lbrack may be provided. + lbrack = lbrack or rbrack - 1 + diff = rbrack - lbrack + + # if there is no sign change in `fun` between the brackets, expand + # rbrack - lbrack until a sign change occurs + def interval_contains_root(lbrack, rbrack): + # return true if the signs disagree. + return np.sign(fun(lbrack)) != np.sign(fun(rbrack)) + + while not interval_contains_root(lbrack, rbrack): + diff *= 2 + lbrack = rbrack - diff + + msg = ("The solver could not find a bracket containing a " + "root to an MLE first order condition.") + if np.isinf(lbrack): + raise FitSolverError(msg) + + return lbrack + + +class ksone_gen(rv_continuous): + r"""Kolmogorov-Smirnov one-sided test statistic distribution. + + This is the distribution of the one-sided Kolmogorov-Smirnov (KS) + statistics :math:`D_n^+` and :math:`D_n^-` + for a finite sample size ``n >= 1`` (the shape parameter). + + %(before_notes)s + + See Also + -------- + kstwobign, kstwo, kstest + + Notes + ----- + :math:`D_n^+` and :math:`D_n^-` are given by + + .. math:: + + D_n^+ &= \text{sup}_x (F_n(x) - F(x)),\\ + D_n^- &= \text{sup}_x (F(x) - F_n(x)),\\ + + where :math:`F` is a continuous CDF and :math:`F_n` is an empirical CDF. + `ksone` describes the distribution under the null hypothesis of the KS test + that the empirical CDF corresponds to :math:`n` i.i.d. random variates + with CDF :math:`F`. + + %(after_notes)s + + References + ---------- + .. [1] Birnbaum, Z. W. and Tingey, F.H. "One-sided confidence contours + for probability distribution functions", The Annals of Mathematical + Statistics, 22(4), pp 592-596 (1951). + + %(example)s + + """ + def _argcheck(self, n): + return (n >= 1) & (n == np.round(n)) + + def _shape_info(self): + return [_ShapeInfo("n", True, (1, np.inf), (True, False))] + + def _pdf(self, x, n): + return -scu._smirnovp(n, x) + + def _cdf(self, x, n): + return scu._smirnovc(n, x) + + def _sf(self, x, n): + return sc.smirnov(n, x) + + def _ppf(self, q, n): + return scu._smirnovci(n, q) + + def _isf(self, q, n): + return sc.smirnovi(n, q) + + +ksone = ksone_gen(a=0.0, b=1.0, name='ksone') + + +class kstwo_gen(rv_continuous): + r"""Kolmogorov-Smirnov two-sided test statistic distribution. + + This is the distribution of the two-sided Kolmogorov-Smirnov (KS) + statistic :math:`D_n` for a finite sample size ``n >= 1`` + (the shape parameter). + + %(before_notes)s + + See Also + -------- + kstwobign, ksone, kstest + + Notes + ----- + :math:`D_n` is given by + + .. math:: + + D_n = \text{sup}_x |F_n(x) - F(x)| + + where :math:`F` is a (continuous) CDF and :math:`F_n` is an empirical CDF. + `kstwo` describes the distribution under the null hypothesis of the KS test + that the empirical CDF corresponds to :math:`n` i.i.d. random variates + with CDF :math:`F`. + + %(after_notes)s + + References + ---------- + .. [1] Simard, R., L'Ecuyer, P. "Computing the Two-Sided + Kolmogorov-Smirnov Distribution", Journal of Statistical Software, + Vol 39, 11, 1-18 (2011). + + %(example)s + + """ + def _argcheck(self, n): + return (n >= 1) & (n == np.round(n)) + + def _shape_info(self): + return [_ShapeInfo("n", True, (1, np.inf), (True, False))] + + def _get_support(self, n): + return (0.5/(n if not isinstance(n, Iterable) else np.asanyarray(n)), + 1.0) + + def _pdf(self, x, n): + return kolmognp(n, x) + + def _cdf(self, x, n): + return kolmogn(n, x) + + def _sf(self, x, n): + return kolmogn(n, x, cdf=False) + + def _ppf(self, q, n): + return kolmogni(n, q, cdf=True) + + def _isf(self, q, n): + return kolmogni(n, q, cdf=False) + + +# Use the pdf, (not the ppf) to compute moments +kstwo = kstwo_gen(momtype=0, a=0.0, b=1.0, name='kstwo') + + +class kstwobign_gen(rv_continuous): + r"""Limiting distribution of scaled Kolmogorov-Smirnov two-sided test statistic. + + This is the asymptotic distribution of the two-sided Kolmogorov-Smirnov + statistic :math:`\sqrt{n} D_n` that measures the maximum absolute + distance of the theoretical (continuous) CDF from the empirical CDF. + (see `kstest`). + + %(before_notes)s + + See Also + -------- + ksone, kstwo, kstest + + Notes + ----- + :math:`\sqrt{n} D_n` is given by + + .. math:: + + D_n = \text{sup}_x |F_n(x) - F(x)| + + where :math:`F` is a continuous CDF and :math:`F_n` is an empirical CDF. + `kstwobign` describes the asymptotic distribution (i.e. the limit of + :math:`\sqrt{n} D_n`) under the null hypothesis of the KS test that the + empirical CDF corresponds to i.i.d. random variates with CDF :math:`F`. + + %(after_notes)s + + References + ---------- + .. [1] Feller, W. "On the Kolmogorov-Smirnov Limit Theorems for Empirical + Distributions", Ann. Math. Statist. Vol 19, 177-189 (1948). + + %(example)s + + """ + def _shape_info(self): + return [] + + def _pdf(self, x): + return -scu._kolmogp(x) + + def _cdf(self, x): + return scu._kolmogc(x) + + def _sf(self, x): + return sc.kolmogorov(x) + + def _ppf(self, q): + return scu._kolmogci(q) + + def _isf(self, q): + return sc.kolmogi(q) + + +kstwobign = kstwobign_gen(a=0.0, name='kstwobign') + + +## Normal distribution + +# loc = mu, scale = std +# Keep these implementations out of the class definition so they can be reused +# by other distributions. +_norm_pdf_C = np.sqrt(2*np.pi) +_norm_pdf_logC = np.log(_norm_pdf_C) + + +def _norm_pdf(x): + return np.exp(-x**2/2.0) / _norm_pdf_C + + +def _norm_logpdf(x): + return -x**2 / 2.0 - _norm_pdf_logC + + +def _norm_cdf(x): + return sc.ndtr(x) + + +def _norm_logcdf(x): + return sc.log_ndtr(x) + + +def _norm_ppf(q): + return sc.ndtri(q) + + +def _norm_sf(x): + return _norm_cdf(-x) + + +def _norm_logsf(x): + return _norm_logcdf(-x) + + +def _norm_isf(q): + return -_norm_ppf(q) + + +class norm_gen(rv_continuous): + r"""A normal continuous random variable. + + The location (``loc``) keyword specifies the mean. + The scale (``scale``) keyword specifies the standard deviation. + + %(before_notes)s + + Notes + ----- + The probability density function for `norm` is: + + .. math:: + + f(x) = \frac{\exp(-x^2/2)}{\sqrt{2\pi}} + + for a real number :math:`x`. + + %(after_notes)s + + %(example)s + + """ + def _shape_info(self): + return [] + + def _rvs(self, size=None, random_state=None): + return random_state.standard_normal(size) + + def _pdf(self, x): + # norm.pdf(x) = exp(-x**2/2)/sqrt(2*pi) + return _norm_pdf(x) + + def _logpdf(self, x): + return _norm_logpdf(x) + + def _cdf(self, x): + return _norm_cdf(x) + + def _logcdf(self, x): + return _norm_logcdf(x) + + def _sf(self, x): + return _norm_sf(x) + + def _logsf(self, x): + return _norm_logsf(x) + + def _ppf(self, q): + return _norm_ppf(q) + + def _isf(self, q): + return _norm_isf(q) + + def _stats(self): + return 0.0, 1.0, 0.0, 0.0 + + def _entropy(self): + return 0.5*(np.log(2*np.pi)+1) + + @_call_super_mom + @replace_notes_in_docstring(rv_continuous, notes="""\ + For the normal distribution, method of moments and maximum likelihood + estimation give identical fits, and explicit formulas for the estimates + are available. + This function uses these explicit formulas for the maximum likelihood + estimation of the normal distribution parameters, so the + `optimizer` and `method` arguments are ignored.\n\n""") + def fit(self, data, **kwds): + floc = kwds.pop('floc', None) + fscale = kwds.pop('fscale', None) + + _remove_optimizer_parameters(kwds) + + if floc is not None and fscale is not None: + # This check is for consistency with `rv_continuous.fit`. + # Without this check, this function would just return the + # parameters that were given. + raise ValueError("All parameters fixed. There is nothing to " + "optimize.") + + data = np.asarray(data) + + if not np.isfinite(data).all(): + raise ValueError("The data contains non-finite values.") + + if floc is None: + loc = data.mean() + else: + loc = floc + + if fscale is None: + scale = np.sqrt(((data - loc)**2).mean()) + else: + scale = fscale + + return loc, scale + + def _munp(self, n): + """ + @returns Moments of standard normal distribution for integer n >= 0 + + See eq. 16 of https://arxiv.org/abs/1209.4340v2 + """ + if n % 2 == 0: + return sc.factorial2(n - 1) + else: + return 0. + + +norm = norm_gen(name='norm') + + +class alpha_gen(rv_continuous): + r"""An alpha continuous random variable. + + %(before_notes)s + + Notes + ----- + The probability density function for `alpha` ([1]_, [2]_) is: + + .. math:: + + f(x, a) = \frac{1}{x^2 \Phi(a) \sqrt{2\pi}} * + \exp(-\frac{1}{2} (a-1/x)^2) + + where :math:`\Phi` is the normal CDF, :math:`x > 0`, and :math:`a > 0`. + + `alpha` takes ``a`` as a shape parameter. + + %(after_notes)s + + References + ---------- + .. [1] Johnson, Kotz, and Balakrishnan, "Continuous Univariate + Distributions, Volume 1", Second Edition, John Wiley and Sons, + p. 173 (1994). + .. [2] Anthony A. Salvia, "Reliability applications of the Alpha + Distribution", IEEE Transactions on Reliability, Vol. R-34, + No. 3, pp. 251-252 (1985). + + %(example)s + + """ + _support_mask = rv_continuous._open_support_mask + + def _shape_info(self): + return [_ShapeInfo("a", False, (0, np.inf), (False, False))] + + def _pdf(self, x, a): + # alpha.pdf(x, a) = 1/(x**2*Phi(a)*sqrt(2*pi)) * exp(-1/2 * (a-1/x)**2) + return 1.0/(x**2)/_norm_cdf(a)*_norm_pdf(a-1.0/x) + + def _logpdf(self, x, a): + return -2*np.log(x) + _norm_logpdf(a-1.0/x) - np.log(_norm_cdf(a)) + + def _cdf(self, x, a): + return _norm_cdf(a-1.0/x) / _norm_cdf(a) + + def _ppf(self, q, a): + return 1.0/np.asarray(a - _norm_ppf(q*_norm_cdf(a))) + + def _stats(self, a): + return [np.inf]*2 + [np.nan]*2 + + +alpha = alpha_gen(a=0.0, name='alpha') + + +class anglit_gen(rv_continuous): + r"""An anglit continuous random variable. + + %(before_notes)s + + Notes + ----- + The probability density function for `anglit` is: + + .. math:: + + f(x) = \sin(2x + \pi/2) = \cos(2x) + + for :math:`-\pi/4 \le x \le \pi/4`. + + %(after_notes)s + + %(example)s + + """ + def _shape_info(self): + return [] + + def _pdf(self, x): + # anglit.pdf(x) = sin(2*x + \pi/2) = cos(2*x) + return np.cos(2*x) + + def _cdf(self, x): + return np.sin(x+np.pi/4)**2.0 + + def _sf(self, x): + return np.cos(x + np.pi / 4) ** 2.0 + + def _ppf(self, q): + return np.arcsin(np.sqrt(q))-np.pi/4 + + def _stats(self): + return 0.0, np.pi*np.pi/16-0.5, 0.0, -2*(np.pi**4 - 96)/(np.pi*np.pi-8)**2 + + def _entropy(self): + return 1-np.log(2) + + +anglit = anglit_gen(a=-np.pi/4, b=np.pi/4, name='anglit') + + +class arcsine_gen(rv_continuous): + r"""An arcsine continuous random variable. + + %(before_notes)s + + Notes + ----- + The probability density function for `arcsine` is: + + .. math:: + + f(x) = \frac{1}{\pi \sqrt{x (1-x)}} + + for :math:`0 < x < 1`. + + %(after_notes)s + + %(example)s + + """ + def _shape_info(self): + return [] + + def _pdf(self, x): + # arcsine.pdf(x) = 1/(pi*sqrt(x*(1-x))) + with np.errstate(divide='ignore'): + return 1.0/np.pi/np.sqrt(x*(1-x)) + + def _cdf(self, x): + return 2.0/np.pi*np.arcsin(np.sqrt(x)) + + def _ppf(self, q): + return np.sin(np.pi/2.0*q)**2.0 + + def _stats(self): + mu = 0.5 + mu2 = 1.0/8 + g1 = 0 + g2 = -3.0/2.0 + return mu, mu2, g1, g2 + + def _entropy(self): + return -0.24156447527049044468 + + +arcsine = arcsine_gen(a=0.0, b=1.0, name='arcsine') + + +class FitDataError(ValueError): + """Raised when input data is inconsistent with fixed parameters.""" + # This exception is raised by, for example, beta_gen.fit when both floc + # and fscale are fixed and there are values in the data not in the open + # interval (floc, floc+fscale). + def __init__(self, distr, lower, upper): + self.args = ( + "Invalid values in `data`. Maximum likelihood " + f"estimation with {distr!r} requires that {lower!r} < " + f"(x - loc)/scale < {upper!r} for each x in `data`.", + ) + + +class FitSolverError(FitError): + """ + Raised when a solver fails to converge while fitting a distribution. + """ + # This exception is raised by, for example, beta_gen.fit when + # optimize.fsolve returns with ier != 1. + def __init__(self, mesg): + emsg = "Solver for the MLE equations failed to converge: " + emsg += mesg.replace('\n', '') + self.args = (emsg,) + + +def _beta_mle_a(a, b, n, s1): + # The zeros of this function give the MLE for `a`, with + # `b`, `n` and `s1` given. `s1` is the sum of the logs of + # the data. `n` is the number of data points. + psiab = sc.psi(a + b) + func = s1 - n * (-psiab + sc.psi(a)) + return func + + +def _beta_mle_ab(theta, n, s1, s2): + # Zeros of this function are critical points of + # the maximum likelihood function. Solving this system + # for theta (which contains a and b) gives the MLE for a and b + # given `n`, `s1` and `s2`. `s1` is the sum of the logs of the data, + # and `s2` is the sum of the logs of 1 - data. `n` is the number + # of data points. + a, b = theta + psiab = sc.psi(a + b) + func = [s1 - n * (-psiab + sc.psi(a)), + s2 - n * (-psiab + sc.psi(b))] + return func + + +class beta_gen(rv_continuous): + r"""A beta continuous random variable. + + %(before_notes)s + + Notes + ----- + The probability density function for `beta` is: + + .. math:: + + f(x, a, b) = \frac{\Gamma(a+b) x^{a-1} (1-x)^{b-1}} + {\Gamma(a) \Gamma(b)} + + for :math:`0 <= x <= 1`, :math:`a > 0`, :math:`b > 0`, where + :math:`\Gamma` is the gamma function (`scipy.special.gamma`). + + `beta` takes :math:`a` and :math:`b` as shape parameters. + + %(after_notes)s + + %(example)s + + """ + def _shape_info(self): + ia = _ShapeInfo("a", False, (0, np.inf), (False, False)) + ib = _ShapeInfo("b", False, (0, np.inf), (False, False)) + return [ia, ib] + + def _rvs(self, a, b, size=None, random_state=None): + return random_state.beta(a, b, size) + + def _pdf(self, x, a, b): + # gamma(a+b) * x**(a-1) * (1-x)**(b-1) + # beta.pdf(x, a, b) = ------------------------------------ + # gamma(a)*gamma(b) + with np.errstate(over='ignore'): + return _boost._beta_pdf(x, a, b) + + def _logpdf(self, x, a, b): + lPx = sc.xlog1py(b - 1.0, -x) + sc.xlogy(a - 1.0, x) + lPx -= sc.betaln(a, b) + return lPx + + def _cdf(self, x, a, b): + return _boost._beta_cdf(x, a, b) + + def _sf(self, x, a, b): + return _boost._beta_sf(x, a, b) + + def _isf(self, x, a, b): + with np.errstate(over='ignore'): # see gh-17432 + return _boost._beta_isf(x, a, b) + + def _ppf(self, q, a, b): + with np.errstate(over='ignore'): # see gh-17432 + return _boost._beta_ppf(q, a, b) + + def _stats(self, a, b): + return ( + _boost._beta_mean(a, b), + _boost._beta_variance(a, b), + _boost._beta_skewness(a, b), + _boost._beta_kurtosis_excess(a, b)) + + def _fitstart(self, data): + if isinstance(data, CensoredData): + data = data._uncensor() + + g1 = _skew(data) + g2 = _kurtosis(data) + + def func(x): + a, b = x + sk = 2*(b-a)*np.sqrt(a + b + 1) / (a + b + 2) / np.sqrt(a*b) + ku = a**3 - a**2*(2*b-1) + b**2*(b+1) - 2*a*b*(b+2) + ku /= a*b*(a+b+2)*(a+b+3) + ku *= 6 + return [sk-g1, ku-g2] + a, b = optimize.fsolve(func, (1.0, 1.0)) + return super()._fitstart(data, args=(a, b)) + + @_call_super_mom + @extend_notes_in_docstring(rv_continuous, notes="""\ + In the special case where `method="MLE"` and + both `floc` and `fscale` are given, a + `ValueError` is raised if any value `x` in `data` does not satisfy + `floc < x < floc + fscale`.\n\n""") + def fit(self, data, *args, **kwds): + # Override rv_continuous.fit, so we can more efficiently handle the + # case where floc and fscale are given. + + floc = kwds.get('floc', None) + fscale = kwds.get('fscale', None) + + if floc is None or fscale is None: + # do general fit + return super().fit(data, *args, **kwds) + + # We already got these from kwds, so just pop them. + kwds.pop('floc', None) + kwds.pop('fscale', None) + + f0 = _get_fixed_fit_value(kwds, ['f0', 'fa', 'fix_a']) + f1 = _get_fixed_fit_value(kwds, ['f1', 'fb', 'fix_b']) + + _remove_optimizer_parameters(kwds) + + if f0 is not None and f1 is not None: + # This check is for consistency with `rv_continuous.fit`. + raise ValueError("All parameters fixed. There is nothing to " + "optimize.") + + # Special case: loc and scale are constrained, so we are fitting + # just the shape parameters. This can be done much more efficiently + # than the method used in `rv_continuous.fit`. (See the subsection + # "Two unknown parameters" in the section "Maximum likelihood" of + # the Wikipedia article on the Beta distribution for the formulas.) + + if not np.isfinite(data).all(): + raise ValueError("The data contains non-finite values.") + + # Normalize the data to the interval [0, 1]. + data = (np.ravel(data) - floc) / fscale + if np.any(data <= 0) or np.any(data >= 1): + raise FitDataError("beta", lower=floc, upper=floc + fscale) + + xbar = data.mean() + + if f0 is not None or f1 is not None: + # One of the shape parameters is fixed. + + if f0 is not None: + # The shape parameter a is fixed, so swap the parameters + # and flip the data. We always solve for `a`. The result + # will be swapped back before returning. + b = f0 + data = 1 - data + xbar = 1 - xbar + else: + b = f1 + + # Initial guess for a. Use the formula for the mean of the beta + # distribution, E[x] = a / (a + b), to generate a reasonable + # starting point based on the mean of the data and the given + # value of b. + a = b * xbar / (1 - xbar) + + # Compute the MLE for `a` by solving _beta_mle_a. + theta, info, ier, mesg = optimize.fsolve( + _beta_mle_a, a, + args=(b, len(data), np.log(data).sum()), + full_output=True + ) + if ier != 1: + raise FitSolverError(mesg=mesg) + a = theta[0] + + if f0 is not None: + # The shape parameter a was fixed, so swap back the + # parameters. + a, b = b, a + + else: + # Neither of the shape parameters is fixed. + + # s1 and s2 are used in the extra arguments passed to _beta_mle_ab + # by optimize.fsolve. + s1 = np.log(data).sum() + s2 = sc.log1p(-data).sum() + + # Use the "method of moments" to estimate the initial + # guess for a and b. + fac = xbar * (1 - xbar) / data.var(ddof=0) - 1 + a = xbar * fac + b = (1 - xbar) * fac + + # Compute the MLE for a and b by solving _beta_mle_ab. + theta, info, ier, mesg = optimize.fsolve( + _beta_mle_ab, [a, b], + args=(len(data), s1, s2), + full_output=True + ) + if ier != 1: + raise FitSolverError(mesg=mesg) + a, b = theta + + return a, b, floc, fscale + + def _entropy(self, a, b): + def regular(a, b): + return (sc.betaln(a, b) - (a - 1) * sc.psi(a) - + (b - 1) * sc.psi(b) + (a + b - 2) * sc.psi(a + b)) + + def asymptotic_ab_large(a, b): + sum_ab = a + b + log_term = 0.5 * ( + np.log(2*np.pi) + np.log(a) + np.log(b) - 3*np.log(sum_ab) + 1 + ) + t1 = 110/sum_ab + 20*sum_ab**-2.0 + sum_ab**-3.0 - 2*sum_ab**-4.0 + t2 = -50/a - 10*a**-2.0 - a**-3.0 + a**-4.0 + t3 = -50/b - 10*b**-2.0 - b**-3.0 + b**-4.0 + return log_term + (t1 + t2 + t3) / 120 + + def asymptotic_b_large(a, b): + sum_ab = a + b + t1 = sc.gammaln(a) - (a - 1) * sc.psi(a) + t2 = ( + - 1/(2*b) + 1/(12*b) - b**-2.0/12 - b**-3.0/120 + b**-4.0/120 + + b**-5.0/252 - b**-6.0/252 + 1/sum_ab - 1/(12*sum_ab) + + sum_ab**-2.0/6 + sum_ab**-3.0/120 - sum_ab**-4.0/60 + - sum_ab**-5.0/252 + sum_ab**-6.0/126 + ) + log_term = sum_ab*np.log1p(a/b) + np.log(b) - 2*np.log(sum_ab) + return t1 + t2 + log_term + + def threshold_large(v): + if v == 1.0: + return 1000 + + j = np.log10(v) + digits = int(j) + d = int(v / 10 ** digits) + 2 + return d*10**(7 + j) + + if a >= 4.96e6 and b >= 4.96e6: + return asymptotic_ab_large(a, b) + elif a <= 4.9e6 and b - a >= 1e6 and b >= threshold_large(a): + return asymptotic_b_large(a, b) + elif b <= 4.9e6 and a - b >= 1e6 and a >= threshold_large(b): + return asymptotic_b_large(b, a) + else: + return regular(a, b) + + +beta = beta_gen(a=0.0, b=1.0, name='beta') + + +class betaprime_gen(rv_continuous): + r"""A beta prime continuous random variable. + + %(before_notes)s + + Notes + ----- + The probability density function for `betaprime` is: + + .. math:: + + f(x, a, b) = \frac{x^{a-1} (1+x)^{-a-b}}{\beta(a, b)} + + for :math:`x >= 0`, :math:`a > 0`, :math:`b > 0`, where + :math:`\beta(a, b)` is the beta function (see `scipy.special.beta`). + + `betaprime` takes ``a`` and ``b`` as shape parameters. + + The distribution is related to the `beta` distribution as follows: + If :math:`X` follows a beta distribution with parameters :math:`a, b`, + then :math:`Y = X/(1-X)` has a beta prime distribution with + parameters :math:`a, b` ([1]_). + + The beta prime distribution is a reparametrized version of the + F distribution. The beta prime distribution with shape parameters + ``a`` and ``b`` and ``scale = s`` is equivalent to the F distribution + with parameters ``d1 = 2*a``, ``d2 = 2*b`` and ``scale = (a/b)*s``. + For example, + + >>> from scipy.stats import betaprime, f + >>> x = [1, 2, 5, 10] + >>> a = 12 + >>> b = 5 + >>> betaprime.pdf(x, a, b, scale=2) + array([0.00541179, 0.08331299, 0.14669185, 0.03150079]) + >>> f.pdf(x, 2*a, 2*b, scale=(a/b)*2) + array([0.00541179, 0.08331299, 0.14669185, 0.03150079]) + + %(after_notes)s + + References + ---------- + .. [1] Beta prime distribution, Wikipedia, + https://en.wikipedia.org/wiki/Beta_prime_distribution + + %(example)s + + """ + _support_mask = rv_continuous._open_support_mask + + def _shape_info(self): + ia = _ShapeInfo("a", False, (0, np.inf), (False, False)) + ib = _ShapeInfo("b", False, (0, np.inf), (False, False)) + return [ia, ib] + + def _rvs(self, a, b, size=None, random_state=None): + u1 = gamma.rvs(a, size=size, random_state=random_state) + u2 = gamma.rvs(b, size=size, random_state=random_state) + return u1 / u2 + + def _pdf(self, x, a, b): + # betaprime.pdf(x, a, b) = x**(a-1) * (1+x)**(-a-b) / beta(a, b) + return np.exp(self._logpdf(x, a, b)) + + def _logpdf(self, x, a, b): + return sc.xlogy(a - 1.0, x) - sc.xlog1py(a + b, x) - sc.betaln(a, b) + + def _cdf(self, x, a, b): + # note: f2 is the direct way to compute the cdf if the relationship + # to the beta distribution is used. + # however, for very large x, x/(1+x) == 1. since the distribution + # has very fat tails if b is small, this can cause inaccurate results + # use the following relationship of the incomplete beta function: + # betainc(x, a, b) = 1 - betainc(1-x, b, a) + # see gh-17631 + return _lazywhere( + x > 1, [x, a, b], + lambda x_, a_, b_: beta._sf(1/(1+x_), b_, a_), + f2=lambda x_, a_, b_: beta._cdf(x_/(1+x_), a_, b_)) + + def _sf(self, x, a, b): + return _lazywhere( + x > 1, [x, a, b], + lambda x_, a_, b_: beta._cdf(1/(1+x_), b_, a_), + f2=lambda x_, a_, b_: beta._sf(x_/(1+x_), a_, b_) + ) + + def _ppf(self, p, a, b): + p, a, b = np.broadcast_arrays(p, a, b) + # by default, compute compute the ppf by solving the following: + # p = beta._cdf(x/(1+x), a, b). This implies x = r/(1-r) with + # r = beta._ppf(p, a, b). This can cause numerical issues if r is + # very close to 1. in that case, invert the alternative expression of + # the cdf: p = beta._sf(1/(1+x), b, a). + r = stats.beta._ppf(p, a, b) + with np.errstate(divide='ignore'): + out = r / (1 - r) + i = (r > 0.9999) + out[i] = 1/stats.beta._isf(p[i], b[i], a[i]) - 1 + return out + + def _munp(self, n, a, b): + return _lazywhere( + b > n, (a, b), + lambda a, b: np.prod([(a+i-1)/(b-i) for i in range(1, n+1)], axis=0), + fillvalue=np.inf) + + +betaprime = betaprime_gen(a=0.0, name='betaprime') + + +class bradford_gen(rv_continuous): + r"""A Bradford continuous random variable. + + %(before_notes)s + + Notes + ----- + The probability density function for `bradford` is: + + .. math:: + + f(x, c) = \frac{c}{\log(1+c) (1+cx)} + + for :math:`0 <= x <= 1` and :math:`c > 0`. + + `bradford` takes ``c`` as a shape parameter for :math:`c`. + + %(after_notes)s + + %(example)s + + """ + def _shape_info(self): + return [_ShapeInfo("c", False, (0, np.inf), (False, False))] + + def _pdf(self, x, c): + # bradford.pdf(x, c) = c / (k * (1+c*x)) + return c / (c*x + 1.0) / sc.log1p(c) + + def _cdf(self, x, c): + return sc.log1p(c*x) / sc.log1p(c) + + def _ppf(self, q, c): + return sc.expm1(q * sc.log1p(c)) / c + + def _stats(self, c, moments='mv'): + k = np.log(1.0+c) + mu = (c-k)/(c*k) + mu2 = ((c+2.0)*k-2.0*c)/(2*c*k*k) + g1 = None + g2 = None + if 's' in moments: + g1 = np.sqrt(2)*(12*c*c-9*c*k*(c+2)+2*k*k*(c*(c+3)+3)) + g1 /= np.sqrt(c*(c*(k-2)+2*k))*(3*c*(k-2)+6*k) + if 'k' in moments: + g2 = (c**3*(k-3)*(k*(3*k-16)+24)+12*k*c*c*(k-4)*(k-3) + + 6*c*k*k*(3*k-14) + 12*k**3) + g2 /= 3*c*(c*(k-2)+2*k)**2 + return mu, mu2, g1, g2 + + def _entropy(self, c): + k = np.log(1+c) + return k/2.0 - np.log(c/k) + + +bradford = bradford_gen(a=0.0, b=1.0, name='bradford') + + +class burr_gen(rv_continuous): + r"""A Burr (Type III) continuous random variable. + + %(before_notes)s + + See Also + -------- + fisk : a special case of either `burr` or `burr12` with ``d=1`` + burr12 : Burr Type XII distribution + mielke : Mielke Beta-Kappa / Dagum distribution + + Notes + ----- + The probability density function for `burr` is: + + .. math:: + + f(x; c, d) = c d \frac{x^{-c - 1}} + {{(1 + x^{-c})}^{d + 1}} + + for :math:`x >= 0` and :math:`c, d > 0`. + + `burr` takes ``c`` and ``d`` as shape parameters for :math:`c` and + :math:`d`. + + This is the PDF corresponding to the third CDF given in Burr's list; + specifically, it is equation (11) in Burr's paper [1]_. The distribution + is also commonly referred to as the Dagum distribution [2]_. If the + parameter :math:`c < 1` then the mean of the distribution does not + exist and if :math:`c < 2` the variance does not exist [2]_. + The PDF is finite at the left endpoint :math:`x = 0` if :math:`c * d >= 1`. + + %(after_notes)s + + References + ---------- + .. [1] Burr, I. W. "Cumulative frequency functions", Annals of + Mathematical Statistics, 13(2), pp 215-232 (1942). + .. [2] https://en.wikipedia.org/wiki/Dagum_distribution + .. [3] Kleiber, Christian. "A guide to the Dagum distributions." + Modeling Income Distributions and Lorenz Curves pp 97-117 (2008). + + %(example)s + + """ + # Do not set _support_mask to rv_continuous._open_support_mask + # Whether the left-hand endpoint is suitable for pdf evaluation is dependent + # on the values of c and d: if c*d >= 1, the pdf is finite, otherwise infinite. + + def _shape_info(self): + ic = _ShapeInfo("c", False, (0, np.inf), (False, False)) + id = _ShapeInfo("d", False, (0, np.inf), (False, False)) + return [ic, id] + + def _pdf(self, x, c, d): + # burr.pdf(x, c, d) = c * d * x**(-c-1) * (1+x**(-c))**(-d-1) + output = _lazywhere( + x == 0, [x, c, d], + lambda x_, c_, d_: c_ * d_ * (x_**(c_*d_-1)) / (1 + x_**c_), + f2=lambda x_, c_, d_: (c_ * d_ * (x_ ** (-c_ - 1.0)) / + ((1 + x_ ** (-c_)) ** (d_ + 1.0)))) + if output.ndim == 0: + return output[()] + return output + + def _logpdf(self, x, c, d): + output = _lazywhere( + x == 0, [x, c, d], + lambda x_, c_, d_: (np.log(c_) + np.log(d_) + sc.xlogy(c_*d_ - 1, x_) + - (d_+1) * sc.log1p(x_**(c_))), + f2=lambda x_, c_, d_: (np.log(c_) + np.log(d_) + + sc.xlogy(-c_ - 1, x_) + - sc.xlog1py(d_+1, x_**(-c_)))) + if output.ndim == 0: + return output[()] + return output + + def _cdf(self, x, c, d): + return (1 + x**(-c))**(-d) + + def _logcdf(self, x, c, d): + return sc.log1p(x**(-c)) * (-d) + + def _sf(self, x, c, d): + return np.exp(self._logsf(x, c, d)) + + def _logsf(self, x, c, d): + return np.log1p(- (1 + x**(-c))**(-d)) + + def _ppf(self, q, c, d): + return (q**(-1.0/d) - 1)**(-1.0/c) + + def _isf(self, q, c, d): + _q = sc.xlog1py(-1.0 / d, -q) + return sc.expm1(_q) ** (-1.0 / c) + + def _stats(self, c, d): + nc = np.arange(1, 5).reshape(4,1) / c + # ek is the kth raw moment, e1 is the mean e2-e1**2 variance etc. + e1, e2, e3, e4 = sc.beta(d + nc, 1. - nc) * d + mu = np.where(c > 1.0, e1, np.nan) + mu2_if_c = e2 - mu**2 + mu2 = np.where(c > 2.0, mu2_if_c, np.nan) + g1 = _lazywhere( + c > 3.0, + (c, e1, e2, e3, mu2_if_c), + lambda c, e1, e2, e3, mu2_if_c: ((e3 - 3*e2*e1 + 2*e1**3) + / np.sqrt((mu2_if_c)**3)), + fillvalue=np.nan) + g2 = _lazywhere( + c > 4.0, + (c, e1, e2, e3, e4, mu2_if_c), + lambda c, e1, e2, e3, e4, mu2_if_c: ( + ((e4 - 4*e3*e1 + 6*e2*e1**2 - 3*e1**4) / mu2_if_c**2) - 3), + fillvalue=np.nan) + if np.ndim(c) == 0: + return mu.item(), mu2.item(), g1.item(), g2.item() + return mu, mu2, g1, g2 + + def _munp(self, n, c, d): + def __munp(n, c, d): + nc = 1. * n / c + return d * sc.beta(1.0 - nc, d + nc) + n, c, d = np.asarray(n), np.asarray(c), np.asarray(d) + return _lazywhere((c > n) & (n == n) & (d == d), (c, d, n), + lambda c, d, n: __munp(n, c, d), + np.nan) + + +burr = burr_gen(a=0.0, name='burr') + + +class burr12_gen(rv_continuous): + r"""A Burr (Type XII) continuous random variable. + + %(before_notes)s + + See Also + -------- + fisk : a special case of either `burr` or `burr12` with ``d=1`` + burr : Burr Type III distribution + + Notes + ----- + The probability density function for `burr12` is: + + .. math:: + + f(x; c, d) = c d \frac{x^{c-1}} + {(1 + x^c)^{d + 1}} + + for :math:`x >= 0` and :math:`c, d > 0`. + + `burr12` takes ``c`` and ``d`` as shape parameters for :math:`c` + and :math:`d`. + + This is the PDF corresponding to the twelfth CDF given in Burr's list; + specifically, it is equation (20) in Burr's paper [1]_. + + %(after_notes)s + + The Burr type 12 distribution is also sometimes referred to as + the Singh-Maddala distribution from NIST [2]_. + + References + ---------- + .. [1] Burr, I. W. "Cumulative frequency functions", Annals of + Mathematical Statistics, 13(2), pp 215-232 (1942). + + .. [2] https://www.itl.nist.gov/div898/software/dataplot/refman2/auxillar/b12pdf.htm + + .. [3] "Burr distribution", + https://en.wikipedia.org/wiki/Burr_distribution + + %(example)s + + """ + def _shape_info(self): + ic = _ShapeInfo("c", False, (0, np.inf), (False, False)) + id = _ShapeInfo("d", False, (0, np.inf), (False, False)) + return [ic, id] + + def _pdf(self, x, c, d): + # burr12.pdf(x, c, d) = c * d * x**(c-1) * (1+x**(c))**(-d-1) + return np.exp(self._logpdf(x, c, d)) + + def _logpdf(self, x, c, d): + return np.log(c) + np.log(d) + sc.xlogy(c - 1, x) + sc.xlog1py(-d-1, x**c) + + def _cdf(self, x, c, d): + return -sc.expm1(self._logsf(x, c, d)) + + def _logcdf(self, x, c, d): + return sc.log1p(-(1 + x**c)**(-d)) + + def _sf(self, x, c, d): + return np.exp(self._logsf(x, c, d)) + + def _logsf(self, x, c, d): + return sc.xlog1py(-d, x**c) + + def _ppf(self, q, c, d): + # The following is an implementation of + # ((1 - q)**(-1.0/d) - 1)**(1.0/c) + # that does a better job handling small values of q. + return sc.expm1(-1/d * sc.log1p(-q))**(1/c) + + def _munp(self, n, c, d): + def moment_if_exists(n, c, d): + nc = 1. * n / c + return d * sc.beta(1.0 + nc, d - nc) + + return _lazywhere(c * d > n, (n, c, d), moment_if_exists, + fillvalue=np.nan) + + +burr12 = burr12_gen(a=0.0, name='burr12') + + +class fisk_gen(burr_gen): + r"""A Fisk continuous random variable. + + The Fisk distribution is also known as the log-logistic distribution. + + %(before_notes)s + + See Also + -------- + burr + + Notes + ----- + The probability density function for `fisk` is: + + .. math:: + + f(x, c) = \frac{c x^{c-1}} + {(1 + x^c)^2} + + for :math:`x >= 0` and :math:`c > 0`. + + Please note that the above expression can be transformed into the following + one, which is also commonly used: + + .. math:: + + f(x, c) = \frac{c x^{-c-1}} + {(1 + x^{-c})^2} + + `fisk` takes ``c`` as a shape parameter for :math:`c`. + + `fisk` is a special case of `burr` or `burr12` with ``d=1``. + + Suppose ``X`` is a logistic random variable with location ``l`` + and scale ``s``. Then ``Y = exp(X)`` is a Fisk (log-logistic) + random variable with ``scale = exp(l)`` and shape ``c = 1/s``. + + %(after_notes)s + + %(example)s + + """ + def _shape_info(self): + return [_ShapeInfo("c", False, (0, np.inf), (False, False))] + + def _pdf(self, x, c): + # fisk.pdf(x, c) = c * x**(-c-1) * (1 + x**(-c))**(-2) + return burr._pdf(x, c, 1.0) + + def _cdf(self, x, c): + return burr._cdf(x, c, 1.0) + + def _sf(self, x, c): + return burr._sf(x, c, 1.0) + + def _logpdf(self, x, c): + # fisk.pdf(x, c) = c * x**(-c-1) * (1 + x**(-c))**(-2) + return burr._logpdf(x, c, 1.0) + + def _logcdf(self, x, c): + return burr._logcdf(x, c, 1.0) + + def _logsf(self, x, c): + return burr._logsf(x, c, 1.0) + + def _ppf(self, x, c): + return burr._ppf(x, c, 1.0) + + def _isf(self, q, c): + return burr._isf(q, c, 1.0) + + def _munp(self, n, c): + return burr._munp(n, c, 1.0) + + def _stats(self, c): + return burr._stats(c, 1.0) + + def _entropy(self, c): + return 2 - np.log(c) + + +fisk = fisk_gen(a=0.0, name='fisk') + + +class cauchy_gen(rv_continuous): + r"""A Cauchy continuous random variable. + + %(before_notes)s + + Notes + ----- + The probability density function for `cauchy` is + + .. math:: + + f(x) = \frac{1}{\pi (1 + x^2)} + + for a real number :math:`x`. + + %(after_notes)s + + %(example)s + + """ + def _shape_info(self): + return [] + + def _pdf(self, x): + # cauchy.pdf(x) = 1 / (pi * (1 + x**2)) + return 1.0/np.pi/(1.0+x*x) + + def _cdf(self, x): + return 0.5 + 1.0/np.pi*np.arctan(x) + + def _ppf(self, q): + return np.tan(np.pi*q-np.pi/2.0) + + def _sf(self, x): + return 0.5 - 1.0/np.pi*np.arctan(x) + + def _isf(self, q): + return np.tan(np.pi/2.0-np.pi*q) + + def _stats(self): + return np.nan, np.nan, np.nan, np.nan + + def _entropy(self): + return np.log(4*np.pi) + + def _fitstart(self, data, args=None): + # Initialize ML guesses using quartiles instead of moments. + if isinstance(data, CensoredData): + data = data._uncensor() + p25, p50, p75 = np.percentile(data, [25, 50, 75]) + return p50, (p75 - p25)/2 + + +cauchy = cauchy_gen(name='cauchy') + + +class chi_gen(rv_continuous): + r"""A chi continuous random variable. + + %(before_notes)s + + Notes + ----- + The probability density function for `chi` is: + + .. math:: + + f(x, k) = \frac{1}{2^{k/2-1} \Gamma \left( k/2 \right)} + x^{k-1} \exp \left( -x^2/2 \right) + + for :math:`x >= 0` and :math:`k > 0` (degrees of freedom, denoted ``df`` + in the implementation). :math:`\Gamma` is the gamma function + (`scipy.special.gamma`). + + Special cases of `chi` are: + + - ``chi(1, loc, scale)`` is equivalent to `halfnorm` + - ``chi(2, 0, scale)`` is equivalent to `rayleigh` + - ``chi(3, 0, scale)`` is equivalent to `maxwell` + + `chi` takes ``df`` as a shape parameter. + + %(after_notes)s + + %(example)s + + """ + def _shape_info(self): + return [_ShapeInfo("df", False, (0, np.inf), (False, False))] + + def _rvs(self, df, size=None, random_state=None): + return np.sqrt(chi2.rvs(df, size=size, random_state=random_state)) + + def _pdf(self, x, df): + # x**(df-1) * exp(-x**2/2) + # chi.pdf(x, df) = ------------------------- + # 2**(df/2-1) * gamma(df/2) + return np.exp(self._logpdf(x, df)) + + def _logpdf(self, x, df): + l = np.log(2) - .5*np.log(2)*df - sc.gammaln(.5*df) + return l + sc.xlogy(df - 1., x) - .5*x**2 + + def _cdf(self, x, df): + return sc.gammainc(.5*df, .5*x**2) + + def _sf(self, x, df): + return sc.gammaincc(.5*df, .5*x**2) + + def _ppf(self, q, df): + return np.sqrt(2*sc.gammaincinv(.5*df, q)) + + def _isf(self, q, df): + return np.sqrt(2*sc.gammainccinv(.5*df, q)) + + def _stats(self, df): + # poch(df/2, 1/2) = gamma(df/2 + 1/2) / gamma(df/2) + mu = np.sqrt(2) * sc.poch(0.5 * df, 0.5) + mu2 = df - mu*mu + g1 = (2*mu**3.0 + mu*(1-2*df))/np.asarray(np.power(mu2, 1.5)) + g2 = 2*df*(1.0-df)-6*mu**4 + 4*mu**2 * (2*df-1) + g2 /= np.asarray(mu2**2.0) + return mu, mu2, g1, g2 + + def _entropy(self, df): + + def regular_formula(df): + return (sc.gammaln(.5 * df) + + 0.5 * (df - np.log(2) - (df - 1) * sc.digamma(0.5 * df))) + + def asymptotic_formula(df): + return (0.5 + np.log(np.pi)/2 - (df**-1)/6 - (df**-2)/6 + - 4/45*(df**-3) + (df**-4)/15) + + return _lazywhere(df < 3e2, (df, ), regular_formula, + f2=asymptotic_formula) + + +chi = chi_gen(a=0.0, name='chi') + + +class chi2_gen(rv_continuous): + r"""A chi-squared continuous random variable. + + For the noncentral chi-square distribution, see `ncx2`. + + %(before_notes)s + + See Also + -------- + ncx2 + + Notes + ----- + The probability density function for `chi2` is: + + .. math:: + + f(x, k) = \frac{1}{2^{k/2} \Gamma \left( k/2 \right)} + x^{k/2-1} \exp \left( -x/2 \right) + + for :math:`x > 0` and :math:`k > 0` (degrees of freedom, denoted ``df`` + in the implementation). + + `chi2` takes ``df`` as a shape parameter. + + The chi-squared distribution is a special case of the gamma + distribution, with gamma parameters ``a = df/2``, ``loc = 0`` and + ``scale = 2``. + + %(after_notes)s + + %(example)s + + """ + def _shape_info(self): + return [_ShapeInfo("df", False, (0, np.inf), (False, False))] + + def _rvs(self, df, size=None, random_state=None): + return random_state.chisquare(df, size) + + def _pdf(self, x, df): + # chi2.pdf(x, df) = 1 / (2*gamma(df/2)) * (x/2)**(df/2-1) * exp(-x/2) + return np.exp(self._logpdf(x, df)) + + def _logpdf(self, x, df): + return sc.xlogy(df/2.-1, x) - x/2. - sc.gammaln(df/2.) - (np.log(2)*df)/2. + + def _cdf(self, x, df): + return sc.chdtr(df, x) + + def _sf(self, x, df): + return sc.chdtrc(df, x) + + def _isf(self, p, df): + return sc.chdtri(df, p) + + def _ppf(self, p, df): + return 2*sc.gammaincinv(df/2, p) + + def _stats(self, df): + mu = df + mu2 = 2*df + g1 = 2*np.sqrt(2.0/df) + g2 = 12.0/df + return mu, mu2, g1, g2 + + def _entropy(self, df): + half_df = 0.5 * df + + def regular_formula(half_df): + return (half_df + np.log(2) + sc.gammaln(half_df) + + (1 - half_df) * sc.psi(half_df)) + + def asymptotic_formula(half_df): + # plug in the above formula the following asymptotic + # expansions: + # ln(gamma(a)) ~ (a - 0.5) * ln(a) - a + 0.5 * ln(2 * pi) + + # 1/(12 * a) - 1/(360 * a**3) + # psi(a) ~ ln(a) - 1/(2 * a) - 1/(3 * a**2) + 1/120 * a**4) + c = np.log(2) + 0.5*(1 + np.log(2*np.pi)) + h = 0.5/half_df + return (h*(-2/3 + h*(-1/3 + h*(-4/45 + h/7.5))) + + 0.5*np.log(half_df) + c) + + return _lazywhere(half_df < 125, (half_df, ), + regular_formula, + f2=asymptotic_formula) + + +chi2 = chi2_gen(a=0.0, name='chi2') + + +class cosine_gen(rv_continuous): + r"""A cosine continuous random variable. + + %(before_notes)s + + Notes + ----- + The cosine distribution is an approximation to the normal distribution. + The probability density function for `cosine` is: + + .. math:: + + f(x) = \frac{1}{2\pi} (1+\cos(x)) + + for :math:`-\pi \le x \le \pi`. + + %(after_notes)s + + %(example)s + + """ + def _shape_info(self): + return [] + + def _pdf(self, x): + # cosine.pdf(x) = 1/(2*pi) * (1+cos(x)) + return 1.0/2/np.pi*(1+np.cos(x)) + + def _logpdf(self, x): + c = np.cos(x) + return _lazywhere(c != -1, (c,), + lambda c: np.log1p(c) - np.log(2*np.pi), + fillvalue=-np.inf) + + def _cdf(self, x): + return scu._cosine_cdf(x) + + def _sf(self, x): + return scu._cosine_cdf(-x) + + def _ppf(self, p): + return scu._cosine_invcdf(p) + + def _isf(self, p): + return -scu._cosine_invcdf(p) + + def _stats(self): + v = (np.pi * np.pi / 3.0) - 2.0 + k = -6.0 * (np.pi**4 - 90) / (5.0 * (np.pi * np.pi - 6)**2) + return 0.0, v, 0.0, k + + def _entropy(self): + return np.log(4*np.pi)-1.0 + + +cosine = cosine_gen(a=-np.pi, b=np.pi, name='cosine') + + +class dgamma_gen(rv_continuous): + r"""A double gamma continuous random variable. + + The double gamma distribution is also known as the reflected gamma + distribution [1]_. + + %(before_notes)s + + Notes + ----- + The probability density function for `dgamma` is: + + .. math:: + + f(x, a) = \frac{1}{2\Gamma(a)} |x|^{a-1} \exp(-|x|) + + for a real number :math:`x` and :math:`a > 0`. :math:`\Gamma` is the + gamma function (`scipy.special.gamma`). + + `dgamma` takes ``a`` as a shape parameter for :math:`a`. + + %(after_notes)s + + References + ---------- + .. [1] Johnson, Kotz, and Balakrishnan, "Continuous Univariate + Distributions, Volume 1", Second Edition, John Wiley and Sons + (1994). + + %(example)s + + """ + def _shape_info(self): + return [_ShapeInfo("a", False, (0, np.inf), (False, False))] + + def _rvs(self, a, size=None, random_state=None): + u = random_state.uniform(size=size) + gm = gamma.rvs(a, size=size, random_state=random_state) + return gm * np.where(u >= 0.5, 1, -1) + + def _pdf(self, x, a): + # dgamma.pdf(x, a) = 1 / (2*gamma(a)) * abs(x)**(a-1) * exp(-abs(x)) + ax = abs(x) + return 1.0/(2*sc.gamma(a))*ax**(a-1.0) * np.exp(-ax) + + def _logpdf(self, x, a): + ax = abs(x) + return sc.xlogy(a - 1.0, ax) - ax - np.log(2) - sc.gammaln(a) + + def _cdf(self, x, a): + return np.where(x > 0, + 0.5 + 0.5*sc.gammainc(a, x), + 0.5*sc.gammaincc(a, -x)) + + def _sf(self, x, a): + return np.where(x > 0, + 0.5*sc.gammaincc(a, x), + 0.5 + 0.5*sc.gammainc(a, -x)) + + def _entropy(self, a): + return stats.gamma._entropy(a) - np.log(0.5) + + def _ppf(self, q, a): + return np.where(q > 0.5, + sc.gammaincinv(a, 2*q - 1), + -sc.gammainccinv(a, 2*q)) + + def _isf(self, q, a): + return np.where(q > 0.5, + -sc.gammaincinv(a, 2*q - 1), + sc.gammainccinv(a, 2*q)) + + def _stats(self, a): + mu2 = a*(a+1.0) + return 0.0, mu2, 0.0, (a+2.0)*(a+3.0)/mu2-3.0 + + +dgamma = dgamma_gen(name='dgamma') + + +class dweibull_gen(rv_continuous): + r"""A double Weibull continuous random variable. + + %(before_notes)s + + Notes + ----- + The probability density function for `dweibull` is given by + + .. math:: + + f(x, c) = c / 2 |x|^{c-1} \exp(-|x|^c) + + for a real number :math:`x` and :math:`c > 0`. + + `dweibull` takes ``c`` as a shape parameter for :math:`c`. + + %(after_notes)s + + %(example)s + + """ + def _shape_info(self): + return [_ShapeInfo("c", False, (0, np.inf), (False, False))] + + def _rvs(self, c, size=None, random_state=None): + u = random_state.uniform(size=size) + w = weibull_min.rvs(c, size=size, random_state=random_state) + return w * (np.where(u >= 0.5, 1, -1)) + + def _pdf(self, x, c): + # dweibull.pdf(x, c) = c / 2 * abs(x)**(c-1) * exp(-abs(x)**c) + ax = abs(x) + Px = c / 2.0 * ax**(c-1.0) * np.exp(-ax**c) + return Px + + def _logpdf(self, x, c): + ax = abs(x) + return np.log(c) - np.log(2.0) + sc.xlogy(c - 1.0, ax) - ax**c + + def _cdf(self, x, c): + Cx1 = 0.5 * np.exp(-abs(x)**c) + return np.where(x > 0, 1 - Cx1, Cx1) + + def _ppf(self, q, c): + fac = 2. * np.where(q <= 0.5, q, 1. - q) + fac = np.power(-np.log(fac), 1.0 / c) + return np.where(q > 0.5, fac, -fac) + + def _sf(self, x, c): + half_weibull_min_sf = 0.5 * stats.weibull_min._sf(np.abs(x), c) + return np.where(x > 0, half_weibull_min_sf, 1 - half_weibull_min_sf) + + def _isf(self, q, c): + double_q = 2. * np.where(q <= 0.5, q, 1. - q) + weibull_min_isf = stats.weibull_min._isf(double_q, c) + return np.where(q > 0.5, -weibull_min_isf, weibull_min_isf) + + def _munp(self, n, c): + return (1 - (n % 2)) * sc.gamma(1.0 + 1.0 * n / c) + + # since we know that all odd moments are zeros, return them at once. + # returning Nones from _stats makes the public stats call _munp + # so overall we're saving one or two gamma function evaluations here. + def _stats(self, c): + return 0, None, 0, None + + def _entropy(self, c): + h = stats.weibull_min._entropy(c) - np.log(0.5) + return h + + +dweibull = dweibull_gen(name='dweibull') + + +class expon_gen(rv_continuous): + r"""An exponential continuous random variable. + + %(before_notes)s + + Notes + ----- + The probability density function for `expon` is: + + .. math:: + + f(x) = \exp(-x) + + for :math:`x \ge 0`. + + %(after_notes)s + + A common parameterization for `expon` is in terms of the rate parameter + ``lambda``, such that ``pdf = lambda * exp(-lambda * x)``. This + parameterization corresponds to using ``scale = 1 / lambda``. + + The exponential distribution is a special case of the gamma + distributions, with gamma shape parameter ``a = 1``. + + %(example)s + + """ + def _shape_info(self): + return [] + + def _rvs(self, size=None, random_state=None): + return random_state.standard_exponential(size) + + def _pdf(self, x): + # expon.pdf(x) = exp(-x) + return np.exp(-x) + + def _logpdf(self, x): + return -x + + def _cdf(self, x): + return -sc.expm1(-x) + + def _ppf(self, q): + return -sc.log1p(-q) + + def _sf(self, x): + return np.exp(-x) + + def _logsf(self, x): + return -x + + def _isf(self, q): + return -np.log(q) + + def _stats(self): + return 1.0, 1.0, 2.0, 6.0 + + def _entropy(self): + return 1.0 + + @_call_super_mom + @replace_notes_in_docstring(rv_continuous, notes="""\ + When `method='MLE'`, + this function uses explicit formulas for the maximum likelihood + estimation of the exponential distribution parameters, so the + `optimizer`, `loc` and `scale` keyword arguments are + ignored.\n\n""") + def fit(self, data, *args, **kwds): + if len(args) > 0: + raise TypeError("Too many arguments.") + + floc = kwds.pop('floc', None) + fscale = kwds.pop('fscale', None) + + _remove_optimizer_parameters(kwds) + + if floc is not None and fscale is not None: + # This check is for consistency with `rv_continuous.fit`. + raise ValueError("All parameters fixed. There is nothing to " + "optimize.") + + data = np.asarray(data) + + if not np.isfinite(data).all(): + raise ValueError("The data contains non-finite values.") + + data_min = data.min() + + if floc is None: + # ML estimate of the location is the minimum of the data. + loc = data_min + else: + loc = floc + if data_min < loc: + # There are values that are less than the specified loc. + raise FitDataError("expon", lower=floc, upper=np.inf) + + if fscale is None: + # ML estimate of the scale is the shifted mean. + scale = data.mean() - loc + else: + scale = fscale + + # We expect the return values to be floating point, so ensure it + # by explicitly converting to float. + return float(loc), float(scale) + + +expon = expon_gen(a=0.0, name='expon') + + +class exponnorm_gen(rv_continuous): + r"""An exponentially modified Normal continuous random variable. + + Also known as the exponentially modified Gaussian distribution [1]_. + + %(before_notes)s + + Notes + ----- + The probability density function for `exponnorm` is: + + .. math:: + + f(x, K) = \frac{1}{2K} \exp\left(\frac{1}{2 K^2} - x / K \right) + \text{erfc}\left(-\frac{x - 1/K}{\sqrt{2}}\right) + + where :math:`x` is a real number and :math:`K > 0`. + + It can be thought of as the sum of a standard normal random variable + and an independent exponentially distributed random variable with rate + ``1/K``. + + %(after_notes)s + + An alternative parameterization of this distribution (for example, in + the Wikipedia article [1]_) involves three parameters, :math:`\mu`, + :math:`\lambda` and :math:`\sigma`. + + In the present parameterization this corresponds to having ``loc`` and + ``scale`` equal to :math:`\mu` and :math:`\sigma`, respectively, and + shape parameter :math:`K = 1/(\sigma\lambda)`. + + .. versionadded:: 0.16.0 + + References + ---------- + .. [1] Exponentially modified Gaussian distribution, Wikipedia, + https://en.wikipedia.org/wiki/Exponentially_modified_Gaussian_distribution + + %(example)s + + """ + def _shape_info(self): + return [_ShapeInfo("K", False, (0, np.inf), (False, False))] + + def _rvs(self, K, size=None, random_state=None): + expval = random_state.standard_exponential(size) * K + gval = random_state.standard_normal(size) + return expval + gval + + def _pdf(self, x, K): + return np.exp(self._logpdf(x, K)) + + def _logpdf(self, x, K): + invK = 1.0 / K + exparg = invK * (0.5 * invK - x) + return exparg + _norm_logcdf(x - invK) - np.log(K) + + def _cdf(self, x, K): + invK = 1.0 / K + expval = invK * (0.5 * invK - x) + logprod = expval + _norm_logcdf(x - invK) + return _norm_cdf(x) - np.exp(logprod) + + def _sf(self, x, K): + invK = 1.0 / K + expval = invK * (0.5 * invK - x) + logprod = expval + _norm_logcdf(x - invK) + return _norm_cdf(-x) + np.exp(logprod) + + def _stats(self, K): + K2 = K * K + opK2 = 1.0 + K2 + skw = 2 * K**3 * opK2**(-1.5) + krt = 6.0 * K2 * K2 * opK2**(-2) + return K, opK2, skw, krt + + +exponnorm = exponnorm_gen(name='exponnorm') + + +def _pow1pm1(x, y): + """ + Compute (1 + x)**y - 1. + + Uses expm1 and xlog1py to avoid loss of precision when + (1 + x)**y is close to 1. + + Note that the inverse of this function with respect to x is + ``_pow1pm1(x, 1/y)``. That is, if + + t = _pow1pm1(x, y) + + then + + x = _pow1pm1(t, 1/y) + """ + return np.expm1(sc.xlog1py(y, x)) + + +class exponweib_gen(rv_continuous): + r"""An exponentiated Weibull continuous random variable. + + %(before_notes)s + + See Also + -------- + weibull_min, numpy.random.Generator.weibull + + Notes + ----- + The probability density function for `exponweib` is: + + .. math:: + + f(x, a, c) = a c [1-\exp(-x^c)]^{a-1} \exp(-x^c) x^{c-1} + + and its cumulative distribution function is: + + .. math:: + + F(x, a, c) = [1-\exp(-x^c)]^a + + for :math:`x > 0`, :math:`a > 0`, :math:`c > 0`. + + `exponweib` takes :math:`a` and :math:`c` as shape parameters: + + * :math:`a` is the exponentiation parameter, + with the special case :math:`a=1` corresponding to the + (non-exponentiated) Weibull distribution `weibull_min`. + * :math:`c` is the shape parameter of the non-exponentiated Weibull law. + + %(after_notes)s + + References + ---------- + https://en.wikipedia.org/wiki/Exponentiated_Weibull_distribution + + %(example)s + + """ + def _shape_info(self): + ia = _ShapeInfo("a", False, (0, np.inf), (False, False)) + ic = _ShapeInfo("c", False, (0, np.inf), (False, False)) + return [ia, ic] + + def _pdf(self, x, a, c): + # exponweib.pdf(x, a, c) = + # a * c * (1-exp(-x**c))**(a-1) * exp(-x**c)*x**(c-1) + return np.exp(self._logpdf(x, a, c)) + + def _logpdf(self, x, a, c): + negxc = -x**c + exm1c = -sc.expm1(negxc) + logp = (np.log(a) + np.log(c) + sc.xlogy(a - 1.0, exm1c) + + negxc + sc.xlogy(c - 1.0, x)) + return logp + + def _cdf(self, x, a, c): + exm1c = -sc.expm1(-x**c) + return exm1c**a + + def _ppf(self, q, a, c): + return (-sc.log1p(-q**(1.0/a)))**np.asarray(1.0/c) + + def _sf(self, x, a, c): + return -_pow1pm1(-np.exp(-x**c), a) + + def _isf(self, p, a, c): + return (-np.log(-_pow1pm1(-p, 1/a)))**(1/c) + + +exponweib = exponweib_gen(a=0.0, name='exponweib') + + +class exponpow_gen(rv_continuous): + r"""An exponential power continuous random variable. + + %(before_notes)s + + Notes + ----- + The probability density function for `exponpow` is: + + .. math:: + + f(x, b) = b x^{b-1} \exp(1 + x^b - \exp(x^b)) + + for :math:`x \ge 0`, :math:`b > 0`. Note that this is a different + distribution from the exponential power distribution that is also known + under the names "generalized normal" or "generalized Gaussian". + + `exponpow` takes ``b`` as a shape parameter for :math:`b`. + + %(after_notes)s + + References + ---------- + http://www.math.wm.edu/~leemis/chart/UDR/PDFs/Exponentialpower.pdf + + %(example)s + + """ + def _shape_info(self): + return [_ShapeInfo("b", False, (0, np.inf), (False, False))] + + def _pdf(self, x, b): + # exponpow.pdf(x, b) = b * x**(b-1) * exp(1 + x**b - exp(x**b)) + return np.exp(self._logpdf(x, b)) + + def _logpdf(self, x, b): + xb = x**b + f = 1 + np.log(b) + sc.xlogy(b - 1.0, x) + xb - np.exp(xb) + return f + + def _cdf(self, x, b): + return -sc.expm1(-sc.expm1(x**b)) + + def _sf(self, x, b): + return np.exp(-sc.expm1(x**b)) + + def _isf(self, x, b): + return (sc.log1p(-np.log(x)))**(1./b) + + def _ppf(self, q, b): + return pow(sc.log1p(-sc.log1p(-q)), 1.0/b) + + +exponpow = exponpow_gen(a=0.0, name='exponpow') + + +class fatiguelife_gen(rv_continuous): + r"""A fatigue-life (Birnbaum-Saunders) continuous random variable. + + %(before_notes)s + + Notes + ----- + The probability density function for `fatiguelife` is: + + .. math:: + + f(x, c) = \frac{x+1}{2c\sqrt{2\pi x^3}} \exp(-\frac{(x-1)^2}{2x c^2}) + + for :math:`x >= 0` and :math:`c > 0`. + + `fatiguelife` takes ``c`` as a shape parameter for :math:`c`. + + %(after_notes)s + + References + ---------- + .. [1] "Birnbaum-Saunders distribution", + https://en.wikipedia.org/wiki/Birnbaum-Saunders_distribution + + %(example)s + + """ + _support_mask = rv_continuous._open_support_mask + + def _shape_info(self): + return [_ShapeInfo("c", False, (0, np.inf), (False, False))] + + def _rvs(self, c, size=None, random_state=None): + z = random_state.standard_normal(size) + x = 0.5*c*z + x2 = x*x + t = 1.0 + 2*x2 + 2*x*np.sqrt(1 + x2) + return t + + def _pdf(self, x, c): + # fatiguelife.pdf(x, c) = + # (x+1) / (2*c*sqrt(2*pi*x**3)) * exp(-(x-1)**2/(2*x*c**2)) + return np.exp(self._logpdf(x, c)) + + def _logpdf(self, x, c): + return (np.log(x+1) - (x-1)**2 / (2.0*x*c**2) - np.log(2*c) - + 0.5*(np.log(2*np.pi) + 3*np.log(x))) + + def _cdf(self, x, c): + return _norm_cdf(1.0 / c * (np.sqrt(x) - 1.0/np.sqrt(x))) + + def _ppf(self, q, c): + tmp = c * _norm_ppf(q) + return 0.25 * (tmp + np.sqrt(tmp**2 + 4))**2 + + def _sf(self, x, c): + return _norm_sf(1.0 / c * (np.sqrt(x) - 1.0/np.sqrt(x))) + + def _isf(self, q, c): + tmp = -c * _norm_ppf(q) + return 0.25 * (tmp + np.sqrt(tmp**2 + 4))**2 + + def _stats(self, c): + # NB: the formula for kurtosis in wikipedia seems to have an error: + # it's 40, not 41. At least it disagrees with the one from Wolfram + # Alpha. And the latter one, below, passes the tests, while the wiki + # one doesn't So far I didn't have the guts to actually check the + # coefficients from the expressions for the raw moments. + c2 = c*c + mu = c2 / 2.0 + 1.0 + den = 5.0 * c2 + 4.0 + mu2 = c2*den / 4.0 + g1 = 4 * c * (11*c2 + 6.0) / np.power(den, 1.5) + g2 = 6 * c2 * (93*c2 + 40.0) / den**2.0 + return mu, mu2, g1, g2 + + +fatiguelife = fatiguelife_gen(a=0.0, name='fatiguelife') + + +class foldcauchy_gen(rv_continuous): + r"""A folded Cauchy continuous random variable. + + %(before_notes)s + + Notes + ----- + The probability density function for `foldcauchy` is: + + .. math:: + + f(x, c) = \frac{1}{\pi (1+(x-c)^2)} + \frac{1}{\pi (1+(x+c)^2)} + + for :math:`x \ge 0` and :math:`c \ge 0`. + + `foldcauchy` takes ``c`` as a shape parameter for :math:`c`. + + %(example)s + + """ + def _argcheck(self, c): + return c >= 0 + + def _shape_info(self): + return [_ShapeInfo("c", False, (0, np.inf), (True, False))] + + def _rvs(self, c, size=None, random_state=None): + return abs(cauchy.rvs(loc=c, size=size, + random_state=random_state)) + + def _pdf(self, x, c): + # foldcauchy.pdf(x, c) = 1/(pi*(1+(x-c)**2)) + 1/(pi*(1+(x+c)**2)) + return 1.0/np.pi*(1.0/(1+(x-c)**2) + 1.0/(1+(x+c)**2)) + + def _cdf(self, x, c): + return 1.0/np.pi*(np.arctan(x-c) + np.arctan(x+c)) + + def _sf(self, x, c): + # 1 - CDF(x, c) = 1 - (atan(x - c) + atan(x + c))/pi + # = ((pi/2 - atan(x - c)) + (pi/2 - atan(x + c)))/pi + # = (acot(x - c) + acot(x + c))/pi + # = (atan2(1, x - c) + atan2(1, x + c))/pi + return (np.arctan2(1, x - c) + np.arctan2(1, x + c))/np.pi + + def _stats(self, c): + return np.inf, np.inf, np.nan, np.nan + + +foldcauchy = foldcauchy_gen(a=0.0, name='foldcauchy') + + +class f_gen(rv_continuous): + r"""An F continuous random variable. + + For the noncentral F distribution, see `ncf`. + + %(before_notes)s + + See Also + -------- + ncf + + Notes + ----- + The F distribution with :math:`df_1 > 0` and :math:`df_2 > 0` degrees of freedom is + the distribution of the ratio of two independent chi-squared distributions with + :math:`df_1` and :math:`df_2` degrees of freedom, after rescaling by + :math:`df_2 / df_1`. + + The probability density function for `f` is: + + .. math:: + + f(x, df_1, df_2) = \frac{df_2^{df_2/2} df_1^{df_1/2} x^{df_1 / 2-1}} + {(df_2+df_1 x)^{(df_1+df_2)/2} + B(df_1/2, df_2/2)} + + for :math:`x > 0`. + + `f` accepts shape parameters ``dfn`` and ``dfd`` for :math:`df_1`, the degrees of + freedom of the chi-squared distribution in the numerator, and :math:`df_2`, the + degrees of freedom of the chi-squared distribution in the denominator, respectively. + + %(after_notes)s + + %(example)s + + """ + def _shape_info(self): + idfn = _ShapeInfo("dfn", False, (0, np.inf), (False, False)) + idfd = _ShapeInfo("dfd", False, (0, np.inf), (False, False)) + return [idfn, idfd] + + def _rvs(self, dfn, dfd, size=None, random_state=None): + return random_state.f(dfn, dfd, size) + + def _pdf(self, x, dfn, dfd): + # df2**(df2/2) * df1**(df1/2) * x**(df1/2-1) + # F.pdf(x, df1, df2) = -------------------------------------------- + # (df2+df1*x)**((df1+df2)/2) * B(df1/2, df2/2) + return np.exp(self._logpdf(x, dfn, dfd)) + + def _logpdf(self, x, dfn, dfd): + n = 1.0 * dfn + m = 1.0 * dfd + lPx = (m/2 * np.log(m) + n/2 * np.log(n) + sc.xlogy(n/2 - 1, x) + - (((n+m)/2) * np.log(m + n*x) + sc.betaln(n/2, m/2))) + return lPx + + def _cdf(self, x, dfn, dfd): + return sc.fdtr(dfn, dfd, x) + + def _sf(self, x, dfn, dfd): + return sc.fdtrc(dfn, dfd, x) + + def _ppf(self, q, dfn, dfd): + return sc.fdtri(dfn, dfd, q) + + def _stats(self, dfn, dfd): + v1, v2 = 1. * dfn, 1. * dfd + v2_2, v2_4, v2_6, v2_8 = v2 - 2., v2 - 4., v2 - 6., v2 - 8. + + mu = _lazywhere( + v2 > 2, (v2, v2_2), + lambda v2, v2_2: v2 / v2_2, + np.inf) + + mu2 = _lazywhere( + v2 > 4, (v1, v2, v2_2, v2_4), + lambda v1, v2, v2_2, v2_4: + 2 * v2 * v2 * (v1 + v2_2) / (v1 * v2_2**2 * v2_4), + np.inf) + + g1 = _lazywhere( + v2 > 6, (v1, v2_2, v2_4, v2_6), + lambda v1, v2_2, v2_4, v2_6: + (2 * v1 + v2_2) / v2_6 * np.sqrt(v2_4 / (v1 * (v1 + v2_2))), + np.nan) + g1 *= np.sqrt(8.) + + g2 = _lazywhere( + v2 > 8, (g1, v2_6, v2_8), + lambda g1, v2_6, v2_8: (8 + g1 * g1 * v2_6) / v2_8, + np.nan) + g2 *= 3. / 2. + + return mu, mu2, g1, g2 + + def _entropy(self, dfn, dfd): + # the formula found in literature is incorrect. This one yields the + # same result as numerical integration using the generic entropy + # definition. This is also tested in tests/test_conntinous_basic + half_dfn = 0.5 * dfn + half_dfd = 0.5 * dfd + half_sum = 0.5 * (dfn + dfd) + + return (np.log(dfd) - np.log(dfn) + sc.betaln(half_dfn, half_dfd) + + (1 - half_dfn) * sc.psi(half_dfn) - (1 + half_dfd) * + sc.psi(half_dfd) + half_sum * sc.psi(half_sum)) + + +f = f_gen(a=0.0, name='f') + + +## Folded Normal +## abs(Z) where (Z is normal with mu=L and std=S so that c=abs(L)/S) +## +## note: regress docs have scale parameter correct, but first parameter +## he gives is a shape parameter A = c * scale + +## Half-normal is folded normal with shape-parameter c=0. + +class foldnorm_gen(rv_continuous): + r"""A folded normal continuous random variable. + + %(before_notes)s + + Notes + ----- + The probability density function for `foldnorm` is: + + .. math:: + + f(x, c) = \sqrt{2/\pi} cosh(c x) \exp(-\frac{x^2+c^2}{2}) + + for :math:`x \ge 0` and :math:`c \ge 0`. + + `foldnorm` takes ``c`` as a shape parameter for :math:`c`. + + %(after_notes)s + + %(example)s + + """ + def _argcheck(self, c): + return c >= 0 + + def _shape_info(self): + return [_ShapeInfo("c", False, (0, np.inf), (True, False))] + + def _rvs(self, c, size=None, random_state=None): + return abs(random_state.standard_normal(size) + c) + + def _pdf(self, x, c): + # foldnormal.pdf(x, c) = sqrt(2/pi) * cosh(c*x) * exp(-(x**2+c**2)/2) + return _norm_pdf(x + c) + _norm_pdf(x-c) + + def _cdf(self, x, c): + sqrt_two = np.sqrt(2) + return 0.5 * (sc.erf((x - c)/sqrt_two) + sc.erf((x + c)/sqrt_two)) + + def _sf(self, x, c): + return _norm_sf(x - c) + _norm_sf(x + c) + + def _stats(self, c): + # Regina C. Elandt, Technometrics 3, 551 (1961) + # https://www.jstor.org/stable/1266561 + # + c2 = c*c + expfac = np.exp(-0.5*c2) / np.sqrt(2.*np.pi) + + mu = 2.*expfac + c * sc.erf(c/np.sqrt(2)) + mu2 = c2 + 1 - mu*mu + + g1 = 2. * (mu*mu*mu - c2*mu - expfac) + g1 /= np.power(mu2, 1.5) + + g2 = c2 * (c2 + 6.) + 3 + 8.*expfac*mu + g2 += (2. * (c2 - 3.) - 3. * mu**2) * mu**2 + g2 = g2 / mu2**2.0 - 3. + + return mu, mu2, g1, g2 + + +foldnorm = foldnorm_gen(a=0.0, name='foldnorm') + + +class weibull_min_gen(rv_continuous): + r"""Weibull minimum continuous random variable. + + The Weibull Minimum Extreme Value distribution, from extreme value theory + (Fisher-Gnedenko theorem), is also often simply called the Weibull + distribution. It arises as the limiting distribution of the rescaled + minimum of iid random variables. + + %(before_notes)s + + See Also + -------- + weibull_max, numpy.random.Generator.weibull, exponweib + + Notes + ----- + The probability density function for `weibull_min` is: + + .. math:: + + f(x, c) = c x^{c-1} \exp(-x^c) + + for :math:`x > 0`, :math:`c > 0`. + + `weibull_min` takes ``c`` as a shape parameter for :math:`c`. + (named :math:`k` in Wikipedia article and :math:`a` in + ``numpy.random.weibull``). Special shape values are :math:`c=1` and + :math:`c=2` where Weibull distribution reduces to the `expon` and + `rayleigh` distributions respectively. + + Suppose ``X`` is an exponentially distributed random variable with + scale ``s``. Then ``Y = X**k`` is `weibull_min` distributed with shape + ``c = 1/k`` and scale ``s**k``. + + %(after_notes)s + + References + ---------- + https://en.wikipedia.org/wiki/Weibull_distribution + + https://en.wikipedia.org/wiki/Fisher-Tippett-Gnedenko_theorem + + %(example)s + + """ + def _shape_info(self): + return [_ShapeInfo("c", False, (0, np.inf), (False, False))] + + def _pdf(self, x, c): + # weibull_min.pdf(x, c) = c * x**(c-1) * exp(-x**c) + return c*pow(x, c-1)*np.exp(-pow(x, c)) + + def _logpdf(self, x, c): + return np.log(c) + sc.xlogy(c - 1, x) - pow(x, c) + + def _cdf(self, x, c): + return -sc.expm1(-pow(x, c)) + + def _ppf(self, q, c): + return pow(-sc.log1p(-q), 1.0/c) + + def _sf(self, x, c): + return np.exp(self._logsf(x, c)) + + def _logsf(self, x, c): + return -pow(x, c) + + def _isf(self, q, c): + return (-np.log(q))**(1/c) + + def _munp(self, n, c): + return sc.gamma(1.0+n*1.0/c) + + def _entropy(self, c): + return -_EULER / c - np.log(c) + _EULER + 1 + + @extend_notes_in_docstring(rv_continuous, notes="""\ + If ``method='mm'``, parameters fixed by the user are respected, and the + remaining parameters are used to match distribution and sample moments + where possible. For example, if the user fixes the location with + ``floc``, the parameters will only match the distribution skewness and + variance to the sample skewness and variance; no attempt will be made + to match the means or minimize a norm of the errors. + \n\n""") + def fit(self, data, *args, **kwds): + + if isinstance(data, CensoredData): + if data.num_censored() == 0: + data = data._uncensor() + else: + return super().fit(data, *args, **kwds) + + if kwds.pop('superfit', False): + return super().fit(data, *args, **kwds) + + # this extracts fixed shape, location, and scale however they + # are specified, and also leaves them in `kwds` + data, fc, floc, fscale = _check_fit_input_parameters(self, data, + args, kwds) + method = kwds.get("method", "mle").lower() + + # See https://en.wikipedia.org/wiki/Weibull_distribution#Moments for + # moment formulas. + def skew(c): + gamma1 = sc.gamma(1+1/c) + gamma2 = sc.gamma(1+2/c) + gamma3 = sc.gamma(1+3/c) + num = 2 * gamma1**3 - 3*gamma1*gamma2 + gamma3 + den = (gamma2 - gamma1**2)**(3/2) + return num/den + + # For c in [1e2, 3e4], population skewness appears to approach + # asymptote near -1.139, but past c > 3e4, skewness begins to vary + # wildly, and MoM won't provide a good guess. Get out early. + s = stats.skew(data) + max_c = 1e4 + s_min = skew(max_c) + if s < s_min and method != "mm" and fc is None and not args: + return super().fit(data, *args, **kwds) + + # If method is method of moments, we don't need the user's guesses. + # Otherwise, extract the guesses from args and kwds. + if method == "mm": + c, loc, scale = None, None, None + else: + c = args[0] if len(args) else None + loc = kwds.pop('loc', None) + scale = kwds.pop('scale', None) + + if fc is None and c is None: # not fixed and no guess: use MoM + # Solve for c that matches sample distribution skewness to sample + # skewness. + # we start having numerical issues with `weibull_min` with + # parameters outside this range - and not just in this method. + # We could probably improve the situation by doing everything + # in the log space, but that is for another time. + c = root_scalar(lambda c: skew(c) - s, bracket=[0.02, max_c], + method='bisect').root + elif fc is not None: # fixed: use it + c = fc + + if fscale is None and scale is None: + v = np.var(data) + scale = np.sqrt(v / (sc.gamma(1+2/c) - sc.gamma(1+1/c)**2)) + elif fscale is not None: + scale = fscale + + if floc is None and loc is None: + m = np.mean(data) + loc = m - scale*sc.gamma(1 + 1/c) + elif floc is not None: + loc = floc + + if method == 'mm': + return c, loc, scale + else: + # At this point, parameter "guesses" may equal the fixed parameters + # in kwds. No harm in passing them as guesses, too. + return super().fit(data, c, loc=loc, scale=scale, **kwds) + + +weibull_min = weibull_min_gen(a=0.0, name='weibull_min') + + +class truncweibull_min_gen(rv_continuous): + r"""A doubly truncated Weibull minimum continuous random variable. + + %(before_notes)s + + See Also + -------- + weibull_min, truncexpon + + Notes + ----- + The probability density function for `truncweibull_min` is: + + .. math:: + + f(x, a, b, c) = \frac{c x^{c-1} \exp(-x^c)}{\exp(-a^c) - \exp(-b^c)} + + for :math:`a < x <= b`, :math:`0 \le a < b` and :math:`c > 0`. + + `truncweibull_min` takes :math:`a`, :math:`b`, and :math:`c` as shape + parameters. + + Notice that the truncation values, :math:`a` and :math:`b`, are defined in + standardized form: + + .. math:: + + a = (u_l - loc)/scale + b = (u_r - loc)/scale + + where :math:`u_l` and :math:`u_r` are the specific left and right + truncation values, respectively. In other words, the support of the + distribution becomes :math:`(a*scale + loc) < x <= (b*scale + loc)` when + :math:`loc` and/or :math:`scale` are provided. + + %(after_notes)s + + References + ---------- + + .. [1] Rinne, H. "The Weibull Distribution: A Handbook". CRC Press (2009). + + %(example)s + + """ + def _argcheck(self, c, a, b): + return (a >= 0.) & (b > a) & (c > 0.) + + def _shape_info(self): + ic = _ShapeInfo("c", False, (0, np.inf), (False, False)) + ia = _ShapeInfo("a", False, (0, np.inf), (True, False)) + ib = _ShapeInfo("b", False, (0, np.inf), (False, False)) + return [ic, ia, ib] + + def _fitstart(self, data): + # Arbitrary, but default a=b=c=1 is not valid + return super()._fitstart(data, args=(1, 0, 1)) + + def _get_support(self, c, a, b): + return a, b + + def _pdf(self, x, c, a, b): + denum = (np.exp(-pow(a, c)) - np.exp(-pow(b, c))) + return (c * pow(x, c-1) * np.exp(-pow(x, c))) / denum + + def _logpdf(self, x, c, a, b): + logdenum = np.log(np.exp(-pow(a, c)) - np.exp(-pow(b, c))) + return np.log(c) + sc.xlogy(c - 1, x) - pow(x, c) - logdenum + + def _cdf(self, x, c, a, b): + num = (np.exp(-pow(a, c)) - np.exp(-pow(x, c))) + denum = (np.exp(-pow(a, c)) - np.exp(-pow(b, c))) + return num / denum + + def _logcdf(self, x, c, a, b): + lognum = np.log(np.exp(-pow(a, c)) - np.exp(-pow(x, c))) + logdenum = np.log(np.exp(-pow(a, c)) - np.exp(-pow(b, c))) + return lognum - logdenum + + def _sf(self, x, c, a, b): + num = (np.exp(-pow(x, c)) - np.exp(-pow(b, c))) + denum = (np.exp(-pow(a, c)) - np.exp(-pow(b, c))) + return num / denum + + def _logsf(self, x, c, a, b): + lognum = np.log(np.exp(-pow(x, c)) - np.exp(-pow(b, c))) + logdenum = np.log(np.exp(-pow(a, c)) - np.exp(-pow(b, c))) + return lognum - logdenum + + def _isf(self, q, c, a, b): + return pow( + -np.log((1 - q) * np.exp(-pow(b, c)) + q * np.exp(-pow(a, c))), 1/c + ) + + def _ppf(self, q, c, a, b): + return pow( + -np.log((1 - q) * np.exp(-pow(a, c)) + q * np.exp(-pow(b, c))), 1/c + ) + + def _munp(self, n, c, a, b): + gamma_fun = sc.gamma(n/c + 1.) * ( + sc.gammainc(n/c + 1., pow(b, c)) - sc.gammainc(n/c + 1., pow(a, c)) + ) + denum = (np.exp(-pow(a, c)) - np.exp(-pow(b, c))) + return gamma_fun / denum + + +truncweibull_min = truncweibull_min_gen(name='truncweibull_min') + + +class weibull_max_gen(rv_continuous): + r"""Weibull maximum continuous random variable. + + The Weibull Maximum Extreme Value distribution, from extreme value theory + (Fisher-Gnedenko theorem), is the limiting distribution of rescaled + maximum of iid random variables. This is the distribution of -X + if X is from the `weibull_min` function. + + %(before_notes)s + + See Also + -------- + weibull_min + + Notes + ----- + The probability density function for `weibull_max` is: + + .. math:: + + f(x, c) = c (-x)^{c-1} \exp(-(-x)^c) + + for :math:`x < 0`, :math:`c > 0`. + + `weibull_max` takes ``c`` as a shape parameter for :math:`c`. + + %(after_notes)s + + References + ---------- + https://en.wikipedia.org/wiki/Weibull_distribution + + https://en.wikipedia.org/wiki/Fisher-Tippett-Gnedenko_theorem + + %(example)s + + """ + def _shape_info(self): + return [_ShapeInfo("c", False, (0, np.inf), (False, False))] + + def _pdf(self, x, c): + # weibull_max.pdf(x, c) = c * (-x)**(c-1) * exp(-(-x)**c) + return c*pow(-x, c-1)*np.exp(-pow(-x, c)) + + def _logpdf(self, x, c): + return np.log(c) + sc.xlogy(c-1, -x) - pow(-x, c) + + def _cdf(self, x, c): + return np.exp(-pow(-x, c)) + + def _logcdf(self, x, c): + return -pow(-x, c) + + def _sf(self, x, c): + return -sc.expm1(-pow(-x, c)) + + def _ppf(self, q, c): + return -pow(-np.log(q), 1.0/c) + + def _munp(self, n, c): + val = sc.gamma(1.0+n*1.0/c) + if int(n) % 2: + sgn = -1 + else: + sgn = 1 + return sgn * val + + def _entropy(self, c): + return -_EULER / c - np.log(c) + _EULER + 1 + + +weibull_max = weibull_max_gen(b=0.0, name='weibull_max') + + +class genlogistic_gen(rv_continuous): + r"""A generalized logistic continuous random variable. + + %(before_notes)s + + Notes + ----- + The probability density function for `genlogistic` is: + + .. math:: + + f(x, c) = c \frac{\exp(-x)} + {(1 + \exp(-x))^{c+1}} + + for real :math:`x` and :math:`c > 0`. In literature, different + generalizations of the logistic distribution can be found. This is the type 1 + generalized logistic distribution according to [1]_. It is also referred to + as the skew-logistic distribution [2]_. + + `genlogistic` takes ``c`` as a shape parameter for :math:`c`. + + %(after_notes)s + + References + ---------- + .. [1] Johnson et al. "Continuous Univariate Distributions", Volume 2, + Wiley. 1995. + .. [2] "Generalized Logistic Distribution", Wikipedia, + https://en.wikipedia.org/wiki/Generalized_logistic_distribution + + %(example)s + + """ + def _shape_info(self): + return [_ShapeInfo("c", False, (0, np.inf), (False, False))] + + def _pdf(self, x, c): + # genlogistic.pdf(x, c) = c * exp(-x) / (1 + exp(-x))**(c+1) + return np.exp(self._logpdf(x, c)) + + def _logpdf(self, x, c): + # Two mathematically equivalent expressions for log(pdf(x, c)): + # log(pdf(x, c)) = log(c) - x - (c + 1)*log(1 + exp(-x)) + # = log(c) + c*x - (c + 1)*log(1 + exp(x)) + mult = -(c - 1) * (x < 0) - 1 + absx = np.abs(x) + return np.log(c) + mult*absx - (c+1) * sc.log1p(np.exp(-absx)) + + def _cdf(self, x, c): + Cx = (1+np.exp(-x))**(-c) + return Cx + + def _logcdf(self, x, c): + return -c * np.log1p(np.exp(-x)) + + def _ppf(self, q, c): + return -np.log(sc.powm1(q, -1.0/c)) + + def _sf(self, x, c): + return -sc.expm1(self._logcdf(x, c)) + + def _isf(self, q, c): + return self._ppf(1 - q, c) + + def _stats(self, c): + mu = _EULER + sc.psi(c) + mu2 = np.pi*np.pi/6.0 + sc.zeta(2, c) + g1 = -2*sc.zeta(3, c) + 2*_ZETA3 + g1 /= np.power(mu2, 1.5) + g2 = np.pi**4/15.0 + 6*sc.zeta(4, c) + g2 /= mu2**2.0 + return mu, mu2, g1, g2 + + def _entropy(self, c): + return _lazywhere(c < 8e6, (c, ), + lambda c: -np.log(c) + sc.psi(c + 1) + _EULER + 1, + # asymptotic expansion: psi(c) ~ log(c) - 1/(2 * c) + # a = -log(c) + psi(c + 1) + # = -log(c) + psi(c) + 1/c + # ~ -log(c) + log(c) - 1/(2 * c) + 1/c + # = 1/(2 * c) + f2=lambda c: 1/(2 * c) + _EULER + 1) + + +genlogistic = genlogistic_gen(name='genlogistic') + + +class genpareto_gen(rv_continuous): + r"""A generalized Pareto continuous random variable. + + %(before_notes)s + + Notes + ----- + The probability density function for `genpareto` is: + + .. math:: + + f(x, c) = (1 + c x)^{-1 - 1/c} + + defined for :math:`x \ge 0` if :math:`c \ge 0`, and for + :math:`0 \le x \le -1/c` if :math:`c < 0`. + + `genpareto` takes ``c`` as a shape parameter for :math:`c`. + + For :math:`c=0`, `genpareto` reduces to the exponential + distribution, `expon`: + + .. math:: + + f(x, 0) = \exp(-x) + + For :math:`c=-1`, `genpareto` is uniform on ``[0, 1]``: + + .. math:: + + f(x, -1) = 1 + + %(after_notes)s + + %(example)s + + """ + def _argcheck(self, c): + return np.isfinite(c) + + def _shape_info(self): + return [_ShapeInfo("c", False, (-np.inf, np.inf), (False, False))] + + def _get_support(self, c): + c = np.asarray(c) + b = _lazywhere(c < 0, (c,), + lambda c: -1. / c, + np.inf) + a = np.where(c >= 0, self.a, self.a) + return a, b + + def _pdf(self, x, c): + # genpareto.pdf(x, c) = (1 + c * x)**(-1 - 1/c) + return np.exp(self._logpdf(x, c)) + + def _logpdf(self, x, c): + return _lazywhere((x == x) & (c != 0), (x, c), + lambda x, c: -sc.xlog1py(c + 1., c*x) / c, + -x) + + def _cdf(self, x, c): + return -sc.inv_boxcox1p(-x, -c) + + def _sf(self, x, c): + return sc.inv_boxcox(-x, -c) + + def _logsf(self, x, c): + return _lazywhere((x == x) & (c != 0), (x, c), + lambda x, c: -sc.log1p(c*x) / c, + -x) + + def _ppf(self, q, c): + return -sc.boxcox1p(-q, -c) + + def _isf(self, q, c): + return -sc.boxcox(q, -c) + + def _stats(self, c, moments='mv'): + if 'm' not in moments: + m = None + else: + m = _lazywhere(c < 1, (c,), + lambda xi: 1/(1 - xi), + np.inf) + if 'v' not in moments: + v = None + else: + v = _lazywhere(c < 1/2, (c,), + lambda xi: 1 / (1 - xi)**2 / (1 - 2*xi), + np.nan) + if 's' not in moments: + s = None + else: + s = _lazywhere(c < 1/3, (c,), + lambda xi: (2 * (1 + xi) * np.sqrt(1 - 2*xi) / + (1 - 3*xi)), + np.nan) + if 'k' not in moments: + k = None + else: + k = _lazywhere(c < 1/4, (c,), + lambda xi: (3 * (1 - 2*xi) * (2*xi**2 + xi + 3) / + (1 - 3*xi) / (1 - 4*xi) - 3), + np.nan) + return m, v, s, k + + def _munp(self, n, c): + def __munp(n, c): + val = 0.0 + k = np.arange(0, n + 1) + for ki, cnk in zip(k, sc.comb(n, k)): + val = val + cnk * (-1) ** ki / (1.0 - c * ki) + return np.where(c * n < 1, val * (-1.0 / c) ** n, np.inf) + return _lazywhere(c != 0, (c,), + lambda c: __munp(n, c), + sc.gamma(n + 1)) + + def _entropy(self, c): + return 1. + c + + +genpareto = genpareto_gen(a=0.0, name='genpareto') + + +class genexpon_gen(rv_continuous): + r"""A generalized exponential continuous random variable. + + %(before_notes)s + + Notes + ----- + The probability density function for `genexpon` is: + + .. math:: + + f(x, a, b, c) = (a + b (1 - \exp(-c x))) + \exp(-a x - b x + \frac{b}{c} (1-\exp(-c x))) + + for :math:`x \ge 0`, :math:`a, b, c > 0`. + + `genexpon` takes :math:`a`, :math:`b` and :math:`c` as shape parameters. + + %(after_notes)s + + References + ---------- + H.K. Ryu, "An Extension of Marshall and Olkin's Bivariate Exponential + Distribution", Journal of the American Statistical Association, 1993. + + N. Balakrishnan, Asit P. Basu (editors), *The Exponential Distribution: + Theory, Methods and Applications*, Gordon and Breach, 1995. + ISBN 10: 2884491929 + + %(example)s + + """ + def _shape_info(self): + ia = _ShapeInfo("a", False, (0, np.inf), (False, False)) + ib = _ShapeInfo("b", False, (0, np.inf), (False, False)) + ic = _ShapeInfo("c", False, (0, np.inf), (False, False)) + return [ia, ib, ic] + + def _pdf(self, x, a, b, c): + # genexpon.pdf(x, a, b, c) = (a + b * (1 - exp(-c*x))) * \ + # exp(-a*x - b*x + b/c * (1-exp(-c*x))) + return (a + b*(-sc.expm1(-c*x)))*np.exp((-a-b)*x + + b*(-sc.expm1(-c*x))/c) + + def _logpdf(self, x, a, b, c): + return np.log(a+b*(-sc.expm1(-c*x))) + (-a-b)*x+b*(-sc.expm1(-c*x))/c + + def _cdf(self, x, a, b, c): + return -sc.expm1((-a-b)*x + b*(-sc.expm1(-c*x))/c) + + def _ppf(self, p, a, b, c): + s = a + b + t = (b - c*np.log1p(-p))/s + return (t + sc.lambertw(-b/s * np.exp(-t)).real)/c + + def _sf(self, x, a, b, c): + return np.exp((-a-b)*x + b*(-sc.expm1(-c*x))/c) + + def _isf(self, p, a, b, c): + s = a + b + t = (b - c*np.log(p))/s + return (t + sc.lambertw(-b/s * np.exp(-t)).real)/c + + +genexpon = genexpon_gen(a=0.0, name='genexpon') + + +class genextreme_gen(rv_continuous): + r"""A generalized extreme value continuous random variable. + + %(before_notes)s + + See Also + -------- + gumbel_r + + Notes + ----- + For :math:`c=0`, `genextreme` is equal to `gumbel_r` with + probability density function + + .. math:: + + f(x) = \exp(-\exp(-x)) \exp(-x), + + where :math:`-\infty < x < \infty`. + + For :math:`c \ne 0`, the probability density function for `genextreme` is: + + .. math:: + + f(x, c) = \exp(-(1-c x)^{1/c}) (1-c x)^{1/c-1}, + + where :math:`-\infty < x \le 1/c` if :math:`c > 0` and + :math:`1/c \le x < \infty` if :math:`c < 0`. + + Note that several sources and software packages use the opposite + convention for the sign of the shape parameter :math:`c`. + + `genextreme` takes ``c`` as a shape parameter for :math:`c`. + + %(after_notes)s + + %(example)s + + """ + def _argcheck(self, c): + return np.isfinite(c) + + def _shape_info(self): + return [_ShapeInfo("c", False, (-np.inf, np.inf), (False, False))] + + def _get_support(self, c): + _b = np.where(c > 0, 1.0 / np.maximum(c, _XMIN), np.inf) + _a = np.where(c < 0, 1.0 / np.minimum(c, -_XMIN), -np.inf) + return _a, _b + + def _loglogcdf(self, x, c): + # Returns log(-log(cdf(x, c))) + return _lazywhere((x == x) & (c != 0), (x, c), + lambda x, c: sc.log1p(-c*x)/c, -x) + + def _pdf(self, x, c): + # genextreme.pdf(x, c) = + # exp(-exp(-x))*exp(-x), for c==0 + # exp(-(1-c*x)**(1/c))*(1-c*x)**(1/c-1), for x \le 1/c, c > 0 + return np.exp(self._logpdf(x, c)) + + def _logpdf(self, x, c): + cx = _lazywhere((x == x) & (c != 0), (x, c), lambda x, c: c*x, 0.0) + logex2 = sc.log1p(-cx) + logpex2 = self._loglogcdf(x, c) + pex2 = np.exp(logpex2) + # Handle special cases + np.putmask(logpex2, (c == 0) & (x == -np.inf), 0.0) + logpdf = _lazywhere(~((cx == 1) | (cx == -np.inf)), + (pex2, logpex2, logex2), + lambda pex2, lpex2, lex2: -pex2 + lpex2 - lex2, + fillvalue=-np.inf) + np.putmask(logpdf, (c == 1) & (x == 1), 0.0) + return logpdf + + def _logcdf(self, x, c): + return -np.exp(self._loglogcdf(x, c)) + + def _cdf(self, x, c): + return np.exp(self._logcdf(x, c)) + + def _sf(self, x, c): + return -sc.expm1(self._logcdf(x, c)) + + def _ppf(self, q, c): + x = -np.log(-np.log(q)) + return _lazywhere((x == x) & (c != 0), (x, c), + lambda x, c: -sc.expm1(-c * x) / c, x) + + def _isf(self, q, c): + x = -np.log(-sc.log1p(-q)) + return _lazywhere((x == x) & (c != 0), (x, c), + lambda x, c: -sc.expm1(-c * x) / c, x) + + def _stats(self, c): + def g(n): + return sc.gamma(n * c + 1) + g1 = g(1) + g2 = g(2) + g3 = g(3) + g4 = g(4) + g2mg12 = np.where(abs(c) < 1e-7, (c*np.pi)**2.0/6.0, g2-g1**2.0) + gam2k = np.where(abs(c) < 1e-7, np.pi**2.0/6.0, + sc.expm1(sc.gammaln(2.0*c+1.0)-2*sc.gammaln(c + 1.0))/c**2.0) + eps = 1e-14 + gamk = np.where(abs(c) < eps, -_EULER, sc.expm1(sc.gammaln(c + 1))/c) + + m = np.where(c < -1.0, np.nan, -gamk) + v = np.where(c < -0.5, np.nan, g1**2.0*gam2k) + + # skewness + sk1 = _lazywhere(c >= -1./3, + (c, g1, g2, g3, g2mg12), + lambda c, g1, g2, g3, g2mg12: + np.sign(c)*(-g3 + (g2 + 2*g2mg12)*g1)/g2mg12**1.5, + fillvalue=np.nan) + sk = np.where(abs(c) <= eps**0.29, 12*np.sqrt(6)*_ZETA3/np.pi**3, sk1) + + # kurtosis + ku1 = _lazywhere(c >= -1./4, + (g1, g2, g3, g4, g2mg12), + lambda g1, g2, g3, g4, g2mg12: + (g4 + (-4*g3 + 3*(g2 + g2mg12)*g1)*g1)/g2mg12**2, + fillvalue=np.nan) + ku = np.where(abs(c) <= (eps)**0.23, 12.0/5.0, ku1-3.0) + return m, v, sk, ku + + def _fitstart(self, data): + if isinstance(data, CensoredData): + data = data._uncensor() + # This is better than the default shape of (1,). + g = _skew(data) + if g < 0: + a = 0.5 + else: + a = -0.5 + return super()._fitstart(data, args=(a,)) + + def _munp(self, n, c): + k = np.arange(0, n+1) + vals = 1.0/c**n * np.sum( + sc.comb(n, k) * (-1)**k * sc.gamma(c*k + 1), + axis=0) + return np.where(c*n > -1, vals, np.inf) + + def _entropy(self, c): + return _EULER*(1 - c) + 1 + + +genextreme = genextreme_gen(name='genextreme') + + +def _digammainv(y): + """Inverse of the digamma function (real positive arguments only). + + This function is used in the `fit` method of `gamma_gen`. + The function uses either optimize.fsolve or optimize.newton + to solve `sc.digamma(x) - y = 0`. There is probably room for + improvement, but currently it works over a wide range of y: + + >>> import numpy as np + >>> rng = np.random.default_rng() + >>> y = 64*rng.standard_normal(1000000) + >>> y.min(), y.max() + (-311.43592651416662, 351.77388222276869) + >>> x = [_digammainv(t) for t in y] + >>> np.abs(sc.digamma(x) - y).max() + 1.1368683772161603e-13 + + """ + _em = 0.5772156649015328606065120 + + def func(x): + return sc.digamma(x) - y + + if y > -0.125: + x0 = np.exp(y) + 0.5 + if y < 10: + # Some experimentation shows that newton reliably converges + # must faster than fsolve in this y range. For larger y, + # newton sometimes fails to converge. + value = optimize.newton(func, x0, tol=1e-10) + return value + elif y > -3: + x0 = np.exp(y/2.332) + 0.08661 + else: + x0 = 1.0 / (-y - _em) + + value, info, ier, mesg = optimize.fsolve(func, x0, xtol=1e-11, + full_output=True) + if ier != 1: + raise RuntimeError("_digammainv: fsolve failed, y = %r" % y) + + return value[0] + + +## Gamma (Use MATLAB and MATHEMATICA (b=theta=scale, a=alpha=shape) definition) + +## gamma(a, loc, scale) with a an integer is the Erlang distribution +## gamma(1, loc, scale) is the Exponential distribution +## gamma(df/2, 0, 2) is the chi2 distribution with df degrees of freedom. + +class gamma_gen(rv_continuous): + r"""A gamma continuous random variable. + + %(before_notes)s + + See Also + -------- + erlang, expon + + Notes + ----- + The probability density function for `gamma` is: + + .. math:: + + f(x, a) = \frac{x^{a-1} e^{-x}}{\Gamma(a)} + + for :math:`x \ge 0`, :math:`a > 0`. Here :math:`\Gamma(a)` refers to the + gamma function. + + `gamma` takes ``a`` as a shape parameter for :math:`a`. + + When :math:`a` is an integer, `gamma` reduces to the Erlang + distribution, and when :math:`a=1` to the exponential distribution. + + Gamma distributions are sometimes parameterized with two variables, + with a probability density function of: + + .. math:: + + f(x, \alpha, \beta) = + \frac{\beta^\alpha x^{\alpha - 1} e^{-\beta x }}{\Gamma(\alpha)} + + Note that this parameterization is equivalent to the above, with + ``scale = 1 / beta``. + + %(after_notes)s + + %(example)s + + """ + def _shape_info(self): + return [_ShapeInfo("a", False, (0, np.inf), (False, False))] + + def _rvs(self, a, size=None, random_state=None): + return random_state.standard_gamma(a, size) + + def _pdf(self, x, a): + # gamma.pdf(x, a) = x**(a-1) * exp(-x) / gamma(a) + return np.exp(self._logpdf(x, a)) + + def _logpdf(self, x, a): + return sc.xlogy(a-1.0, x) - x - sc.gammaln(a) + + def _cdf(self, x, a): + return sc.gammainc(a, x) + + def _sf(self, x, a): + return sc.gammaincc(a, x) + + def _ppf(self, q, a): + return sc.gammaincinv(a, q) + + def _isf(self, q, a): + return sc.gammainccinv(a, q) + + def _stats(self, a): + return a, a, 2.0/np.sqrt(a), 6.0/a + + def _entropy(self, a): + + def regular_formula(a): + return sc.psi(a) * (1-a) + a + sc.gammaln(a) + + def asymptotic_formula(a): + # plug in above formula the expansions: + # psi(a) ~ ln(a) - 1/2a - 1/12a^2 + 1/120a^4 + # gammaln(a) ~ a * ln(a) - a - 1/2 * ln(a) + 1/2 ln(2 * pi) + + # 1/12a - 1/360a^3 + return (0.5 * (1. + np.log(2*np.pi) + np.log(a)) - 1/(3 * a) + - (a**-2.)/12 - (a**-3.)/90 + (a**-4.)/120) + + return _lazywhere(a < 250, (a, ), regular_formula, + f2=asymptotic_formula) + + def _fitstart(self, data): + # The skewness of the gamma distribution is `2 / np.sqrt(a)`. + # We invert that to estimate the shape `a` using the skewness + # of the data. The formula is regularized with 1e-8 in the + # denominator to allow for degenerate data where the skewness + # is close to 0. + if isinstance(data, CensoredData): + data = data._uncensor() + sk = _skew(data) + a = 4 / (1e-8 + sk**2) + return super()._fitstart(data, args=(a,)) + + @extend_notes_in_docstring(rv_continuous, notes="""\ + When the location is fixed by using the argument `floc` + and `method='MLE'`, this + function uses explicit formulas or solves a simpler numerical + problem than the full ML optimization problem. So in that case, + the `optimizer`, `loc` and `scale` arguments are ignored. + \n\n""") + def fit(self, data, *args, **kwds): + floc = kwds.get('floc', None) + method = kwds.get('method', 'mle') + + if (isinstance(data, CensoredData) or + floc is None and method.lower() != 'mm'): + # loc is not fixed or we're not doing standard MLE. + # Use the default fit method. + return super().fit(data, *args, **kwds) + + # We already have this value, so just pop it from kwds. + kwds.pop('floc', None) + + f0 = _get_fixed_fit_value(kwds, ['f0', 'fa', 'fix_a']) + fscale = kwds.pop('fscale', None) + + _remove_optimizer_parameters(kwds) + + if f0 is not None and floc is not None and fscale is not None: + # This check is for consistency with `rv_continuous.fit`. + # Without this check, this function would just return the + # parameters that were given. + raise ValueError("All parameters fixed. There is nothing to " + "optimize.") + + # Fixed location is handled by shifting the data. + data = np.asarray(data) + + if not np.isfinite(data).all(): + raise ValueError("The data contains non-finite values.") + + # Use explicit formulas for mm (gh-19884) + if method.lower() == 'mm': + m1 = np.mean(data) + m2 = np.var(data) + m3 = np.mean((data - m1) ** 3) + a, loc, scale = f0, floc, fscale + # Three unknowns + if a is None and loc is None and scale is None: + scale = m3 / (2 * m2) + # Two unknowns + if loc is None and scale is None: + scale = np.sqrt(m2 / a) + if a is None and scale is None: + scale = m2 / (m1 - loc) + if a is None and loc is None: + a = m2 / (scale ** 2) + # One unknown + if a is None: + a = (m1 - loc) / scale + if loc is None: + loc = m1 - a * scale + if scale is None: + scale = (m1 - loc) / a + return a, loc, scale + + # Special case: loc is fixed. + + # NB: data == loc is ok if a >= 1; the below check is more strict. + if np.any(data <= floc): + raise FitDataError("gamma", lower=floc, upper=np.inf) + + if floc != 0: + # Don't do the subtraction in-place, because `data` might be a + # view of the input array. + data = data - floc + xbar = data.mean() + + # Three cases to handle: + # * shape and scale both free + # * shape fixed, scale free + # * shape free, scale fixed + + if fscale is None: + # scale is free + if f0 is not None: + # shape is fixed + a = f0 + else: + # shape and scale are both free. + # The MLE for the shape parameter `a` is the solution to: + # np.log(a) - sc.digamma(a) - np.log(xbar) + + # np.log(data).mean() = 0 + s = np.log(xbar) - np.log(data).mean() + aest = (3-s + np.sqrt((s-3)**2 + 24*s)) / (12*s) + xa = aest*(1-0.4) + xb = aest*(1+0.4) + a = optimize.brentq(lambda a: np.log(a) - sc.digamma(a) - s, + xa, xb, disp=0) + + # The MLE for the scale parameter is just the data mean + # divided by the shape parameter. + scale = xbar / a + else: + # scale is fixed, shape is free + # The MLE for the shape parameter `a` is the solution to: + # sc.digamma(a) - np.log(data).mean() + np.log(fscale) = 0 + c = np.log(data).mean() - np.log(fscale) + a = _digammainv(c) + scale = fscale + + return a, floc, scale + + +gamma = gamma_gen(a=0.0, name='gamma') + + +class erlang_gen(gamma_gen): + """An Erlang continuous random variable. + + %(before_notes)s + + See Also + -------- + gamma + + Notes + ----- + The Erlang distribution is a special case of the Gamma distribution, with + the shape parameter `a` an integer. Note that this restriction is not + enforced by `erlang`. It will, however, generate a warning the first time + a non-integer value is used for the shape parameter. + + Refer to `gamma` for examples. + + """ + + def _argcheck(self, a): + allint = np.all(np.floor(a) == a) + if not allint: + # An Erlang distribution shouldn't really have a non-integer + # shape parameter, so warn the user. + message = ('The shape parameter of the erlang distribution ' + f'has been given a non-integer value {a!r}.') + warnings.warn(message, RuntimeWarning, stacklevel=3) + return a > 0 + + def _shape_info(self): + return [_ShapeInfo("a", True, (1, np.inf), (True, False))] + + def _fitstart(self, data): + # Override gamma_gen_fitstart so that an integer initial value is + # used. (Also regularize the division, to avoid issues when + # _skew(data) is 0 or close to 0.) + if isinstance(data, CensoredData): + data = data._uncensor() + a = int(4.0 / (1e-8 + _skew(data)**2)) + return super(gamma_gen, self)._fitstart(data, args=(a,)) + + # Trivial override of the fit method, so we can monkey-patch its + # docstring. + @extend_notes_in_docstring(rv_continuous, notes="""\ + The Erlang distribution is generally defined to have integer values + for the shape parameter. This is not enforced by the `erlang` class. + When fitting the distribution, it will generally return a non-integer + value for the shape parameter. By using the keyword argument + `f0=`, the fit method can be constrained to fit the data to + a specific integer shape parameter.""") + def fit(self, data, *args, **kwds): + return super().fit(data, *args, **kwds) + + +erlang = erlang_gen(a=0.0, name='erlang') + + +class gengamma_gen(rv_continuous): + r"""A generalized gamma continuous random variable. + + %(before_notes)s + + See Also + -------- + gamma, invgamma, weibull_min + + Notes + ----- + The probability density function for `gengamma` is ([1]_): + + .. math:: + + f(x, a, c) = \frac{|c| x^{c a-1} \exp(-x^c)}{\Gamma(a)} + + for :math:`x \ge 0`, :math:`a > 0`, and :math:`c \ne 0`. + :math:`\Gamma` is the gamma function (`scipy.special.gamma`). + + `gengamma` takes :math:`a` and :math:`c` as shape parameters. + + %(after_notes)s + + References + ---------- + .. [1] E.W. Stacy, "A Generalization of the Gamma Distribution", + Annals of Mathematical Statistics, Vol 33(3), pp. 1187--1192. + + %(example)s + + """ + def _argcheck(self, a, c): + return (a > 0) & (c != 0) + + def _shape_info(self): + ia = _ShapeInfo("a", False, (0, np.inf), (False, False)) + ic = _ShapeInfo("c", False, (-np.inf, np.inf), (False, False)) + return [ia, ic] + + def _pdf(self, x, a, c): + return np.exp(self._logpdf(x, a, c)) + + def _logpdf(self, x, a, c): + return _lazywhere((x != 0) | (c > 0), (x, c), + lambda x, c: (np.log(abs(c)) + sc.xlogy(c*a - 1, x) + - x**c - sc.gammaln(a)), + fillvalue=-np.inf) + + def _cdf(self, x, a, c): + xc = x**c + val1 = sc.gammainc(a, xc) + val2 = sc.gammaincc(a, xc) + return np.where(c > 0, val1, val2) + + def _rvs(self, a, c, size=None, random_state=None): + r = random_state.standard_gamma(a, size=size) + return r**(1./c) + + def _sf(self, x, a, c): + xc = x**c + val1 = sc.gammainc(a, xc) + val2 = sc.gammaincc(a, xc) + return np.where(c > 0, val2, val1) + + def _ppf(self, q, a, c): + val1 = sc.gammaincinv(a, q) + val2 = sc.gammainccinv(a, q) + return np.where(c > 0, val1, val2)**(1.0/c) + + def _isf(self, q, a, c): + val1 = sc.gammaincinv(a, q) + val2 = sc.gammainccinv(a, q) + return np.where(c > 0, val2, val1)**(1.0/c) + + def _munp(self, n, a, c): + # Pochhammer symbol: sc.pocha,n) = gamma(a+n)/gamma(a) + return sc.poch(a, n*1.0/c) + + def _entropy(self, a, c): + def regular(a, c): + val = sc.psi(a) + A = a * (1 - val) + val / c + B = sc.gammaln(a) - np.log(abs(c)) + h = A + B + return h + + def asymptotic(a, c): + # using asymptotic expansions for gammaln and psi (see gh-18093) + return (norm._entropy() - np.log(a)/2 + - np.log(np.abs(c)) + (a**-1.)/6 - (a**-3.)/90 + + (np.log(a) - (a**-1.)/2 - (a**-2.)/12 + (a**-4.)/120)/c) + + h = _lazywhere(a >= 2e2, (a, c), f=asymptotic, f2=regular) + return h + + +gengamma = gengamma_gen(a=0.0, name='gengamma') + + +class genhalflogistic_gen(rv_continuous): + r"""A generalized half-logistic continuous random variable. + + %(before_notes)s + + Notes + ----- + The probability density function for `genhalflogistic` is: + + .. math:: + + f(x, c) = \frac{2 (1 - c x)^{1/(c-1)}}{[1 + (1 - c x)^{1/c}]^2} + + for :math:`0 \le x \le 1/c`, and :math:`c > 0`. + + `genhalflogistic` takes ``c`` as a shape parameter for :math:`c`. + + %(after_notes)s + + %(example)s + + """ + def _shape_info(self): + return [_ShapeInfo("c", False, (0, np.inf), (False, False))] + + def _get_support(self, c): + return self.a, 1.0/c + + def _pdf(self, x, c): + # genhalflogistic.pdf(x, c) = + # 2 * (1-c*x)**(1/c-1) / (1+(1-c*x)**(1/c))**2 + limit = 1.0/c + tmp = np.asarray(1-c*x) + tmp0 = tmp**(limit-1) + tmp2 = tmp0*tmp + return 2*tmp0 / (1+tmp2)**2 + + def _cdf(self, x, c): + limit = 1.0/c + tmp = np.asarray(1-c*x) + tmp2 = tmp**(limit) + return (1.0-tmp2) / (1+tmp2) + + def _ppf(self, q, c): + return 1.0/c*(1-((1.0-q)/(1.0+q))**c) + + def _entropy(self, c): + return 2 - (2*c+1)*np.log(2) + + +genhalflogistic = genhalflogistic_gen(a=0.0, name='genhalflogistic') + + +class genhyperbolic_gen(rv_continuous): + r"""A generalized hyperbolic continuous random variable. + + %(before_notes)s + + See Also + -------- + t, norminvgauss, geninvgauss, laplace, cauchy + + Notes + ----- + The probability density function for `genhyperbolic` is: + + .. math:: + + f(x, p, a, b) = + \frac{(a^2 - b^2)^{p/2}} + {\sqrt{2\pi}a^{p-1/2} + K_p\Big(\sqrt{a^2 - b^2}\Big)} + e^{bx} \times \frac{K_{p - 1/2} + (a \sqrt{1 + x^2})} + {(\sqrt{1 + x^2})^{1/2 - p}} + + for :math:`x, p \in ( - \infty; \infty)`, + :math:`|b| < a` if :math:`p \ge 0`, + :math:`|b| \le a` if :math:`p < 0`. + :math:`K_{p}(.)` denotes the modified Bessel function of the second + kind and order :math:`p` (`scipy.special.kv`) + + `genhyperbolic` takes ``p`` as a tail parameter, + ``a`` as a shape parameter, + ``b`` as a skewness parameter. + + %(after_notes)s + + The original parameterization of the Generalized Hyperbolic Distribution + is found in [1]_ as follows + + .. math:: + + f(x, \lambda, \alpha, \beta, \delta, \mu) = + \frac{(\gamma/\delta)^\lambda}{\sqrt{2\pi}K_\lambda(\delta \gamma)} + e^{\beta (x - \mu)} \times \frac{K_{\lambda - 1/2} + (\alpha \sqrt{\delta^2 + (x - \mu)^2})} + {(\sqrt{\delta^2 + (x - \mu)^2} / \alpha)^{1/2 - \lambda}} + + for :math:`x \in ( - \infty; \infty)`, + :math:`\gamma := \sqrt{\alpha^2 - \beta^2}`, + :math:`\lambda, \mu \in ( - \infty; \infty)`, + :math:`\delta \ge 0, |\beta| < \alpha` if :math:`\lambda \ge 0`, + :math:`\delta > 0, |\beta| \le \alpha` if :math:`\lambda < 0`. + + The location-scale-based parameterization implemented in + SciPy is based on [2]_, where :math:`a = \alpha\delta`, + :math:`b = \beta\delta`, :math:`p = \lambda`, + :math:`scale=\delta` and :math:`loc=\mu` + + Moments are implemented based on [3]_ and [4]_. + + For the distributions that are a special case such as Student's t, + it is not recommended to rely on the implementation of genhyperbolic. + To avoid potential numerical problems and for performance reasons, + the methods of the specific distributions should be used. + + References + ---------- + .. [1] O. Barndorff-Nielsen, "Hyperbolic Distributions and Distributions + on Hyperbolae", Scandinavian Journal of Statistics, Vol. 5(3), + pp. 151-157, 1978. https://www.jstor.org/stable/4615705 + + .. [2] Eberlein E., Prause K. (2002) The Generalized Hyperbolic Model: + Financial Derivatives and Risk Measures. In: Geman H., Madan D., + Pliska S.R., Vorst T. (eds) Mathematical Finance - Bachelier + Congress 2000. Springer Finance. Springer, Berlin, Heidelberg. + :doi:`10.1007/978-3-662-12429-1_12` + + .. [3] Scott, David J, Würtz, Diethelm, Dong, Christine and Tran, + Thanh Tam, (2009), Moments of the generalized hyperbolic + distribution, MPRA Paper, University Library of Munich, Germany, + https://EconPapers.repec.org/RePEc:pra:mprapa:19081. + + .. [4] E. Eberlein and E. A. von Hammerstein. Generalized hyperbolic + and inverse Gaussian distributions: Limiting cases and approximation + of processes. FDM Preprint 80, April 2003. University of Freiburg. + https://freidok.uni-freiburg.de/fedora/objects/freidok:7974/datastreams/FILE1/content + + %(example)s + + """ + + def _argcheck(self, p, a, b): + return (np.logical_and(np.abs(b) < a, p >= 0) + | np.logical_and(np.abs(b) <= a, p < 0)) + + def _shape_info(self): + ip = _ShapeInfo("p", False, (-np.inf, np.inf), (False, False)) + ia = _ShapeInfo("a", False, (0, np.inf), (True, False)) + ib = _ShapeInfo("b", False, (-np.inf, np.inf), (False, False)) + return [ip, ia, ib] + + def _fitstart(self, data): + # Arbitrary, but the default p = a = b = 1 is not valid; the + # distribution requires |b| < a if p >= 0. + return super()._fitstart(data, args=(1, 1, 0.5)) + + def _logpdf(self, x, p, a, b): + # kve instead of kv works better for large values of p + # and smaller values of sqrt(a^2 - b^2) + @np.vectorize + def _logpdf_single(x, p, a, b): + return _stats.genhyperbolic_logpdf(x, p, a, b) + + return _logpdf_single(x, p, a, b) + + def _pdf(self, x, p, a, b): + # kve instead of kv works better for large values of p + # and smaller values of sqrt(a^2 - b^2) + @np.vectorize + def _pdf_single(x, p, a, b): + return _stats.genhyperbolic_pdf(x, p, a, b) + + return _pdf_single(x, p, a, b) + + # np.vectorize isn't currently designed to be used as a decorator, + # so use a lambda instead. This allows us to decorate the function + # with `np.vectorize` and still provide the `otypes` parameter. + # The first argument to `vectorize` is `func.__get__(object)` for + # compatibility with Python 3.9. In Python 3.10, this can be + # simplified to just `func`. + @lambda func: np.vectorize(func.__get__(object), otypes=[np.float64]) + @staticmethod + def _integrate_pdf(x0, x1, p, a, b): + """ + Integrate the pdf of the genhyberbolic distribution from x0 to x1. + This is a private function used by _cdf() and _sf() only; either x0 + will be -inf or x1 will be inf. + """ + user_data = np.array([p, a, b], float).ctypes.data_as(ctypes.c_void_p) + llc = LowLevelCallable.from_cython(_stats, '_genhyperbolic_pdf', + user_data) + d = np.sqrt((a + b)*(a - b)) + mean = b/d * sc.kv(p + 1, d) / sc.kv(p, d) + epsrel = 1e-10 + epsabs = 0 + if x0 < mean < x1: + # If the interval includes the mean, integrate over the two + # intervals [x0, mean] and [mean, x1] and add. If we try to do + # the integral in one call of quad and the non-infinite endpoint + # is far in the tail, quad might return an incorrect result + # because it does not "see" the peak of the PDF. + intgrl = (integrate.quad(llc, x0, mean, + epsrel=epsrel, epsabs=epsabs)[0] + + integrate.quad(llc, mean, x1, + epsrel=epsrel, epsabs=epsabs)[0]) + else: + intgrl = integrate.quad(llc, x0, x1, + epsrel=epsrel, epsabs=epsabs)[0] + if np.isnan(intgrl): + msg = ("Infinite values encountered in scipy.special.kve. " + "Values replaced by NaN to avoid incorrect results.") + warnings.warn(msg, RuntimeWarning, stacklevel=3) + return max(0.0, min(1.0, intgrl)) + + def _cdf(self, x, p, a, b): + return self._integrate_pdf(-np.inf, x, p, a, b) + + def _sf(self, x, p, a, b): + return self._integrate_pdf(x, np.inf, p, a, b) + + def _rvs(self, p, a, b, size=None, random_state=None): + # note: X = b * V + sqrt(V) * X has a + # generalized hyperbolic distribution + # if X is standard normal and V is + # geninvgauss(p = p, b = t2, loc = loc, scale = t3) + t1 = np.float_power(a, 2) - np.float_power(b, 2) + # b in the GIG + t2 = np.float_power(t1, 0.5) + # scale in the GIG + t3 = np.float_power(t1, - 0.5) + gig = geninvgauss.rvs( + p=p, + b=t2, + scale=t3, + size=size, + random_state=random_state + ) + normst = norm.rvs(size=size, random_state=random_state) + + return b * gig + np.sqrt(gig) * normst + + def _stats(self, p, a, b): + # https://mpra.ub.uni-muenchen.de/19081/1/MPRA_paper_19081.pdf + # https://freidok.uni-freiburg.de/fedora/objects/freidok:7974/datastreams/FILE1/content + # standardized moments + p, a, b = np.broadcast_arrays(p, a, b) + t1 = np.float_power(a, 2) - np.float_power(b, 2) + t1 = np.float_power(t1, 0.5) + t2 = np.float_power(1, 2) * np.float_power(t1, - 1) + integers = np.linspace(0, 4, 5) + # make integers perpendicular to existing dimensions + integers = integers.reshape(integers.shape + (1,) * p.ndim) + b0, b1, b2, b3, b4 = sc.kv(p + integers, t1) + r1, r2, r3, r4 = (b / b0 for b in (b1, b2, b3, b4)) + + m = b * t2 * r1 + v = ( + t2 * r1 + np.float_power(b, 2) * np.float_power(t2, 2) * + (r2 - np.float_power(r1, 2)) + ) + m3e = ( + np.float_power(b, 3) * np.float_power(t2, 3) * + (r3 - 3 * b2 * b1 * np.float_power(b0, -2) + + 2 * np.float_power(r1, 3)) + + 3 * b * np.float_power(t2, 2) * + (r2 - np.float_power(r1, 2)) + ) + s = m3e * np.float_power(v, - 3 / 2) + m4e = ( + np.float_power(b, 4) * np.float_power(t2, 4) * + (r4 - 4 * b3 * b1 * np.float_power(b0, - 2) + + 6 * b2 * np.float_power(b1, 2) * np.float_power(b0, - 3) - + 3 * np.float_power(r1, 4)) + + np.float_power(b, 2) * np.float_power(t2, 3) * + (6 * r3 - 12 * b2 * b1 * np.float_power(b0, - 2) + + 6 * np.float_power(r1, 3)) + + 3 * np.float_power(t2, 2) * r2 + ) + k = m4e * np.float_power(v, -2) - 3 + + return m, v, s, k + + +genhyperbolic = genhyperbolic_gen(name='genhyperbolic') + + +class gompertz_gen(rv_continuous): + r"""A Gompertz (or truncated Gumbel) continuous random variable. + + %(before_notes)s + + Notes + ----- + The probability density function for `gompertz` is: + + .. math:: + + f(x, c) = c \exp(x) \exp(-c (e^x-1)) + + for :math:`x \ge 0`, :math:`c > 0`. + + `gompertz` takes ``c`` as a shape parameter for :math:`c`. + + %(after_notes)s + + %(example)s + + """ + def _shape_info(self): + return [_ShapeInfo("c", False, (0, np.inf), (False, False))] + + def _pdf(self, x, c): + # gompertz.pdf(x, c) = c * exp(x) * exp(-c*(exp(x)-1)) + return np.exp(self._logpdf(x, c)) + + def _logpdf(self, x, c): + return np.log(c) + x - c * sc.expm1(x) + + def _cdf(self, x, c): + return -sc.expm1(-c * sc.expm1(x)) + + def _ppf(self, q, c): + return sc.log1p(-1.0 / c * sc.log1p(-q)) + + def _sf(self, x, c): + return np.exp(-c * sc.expm1(x)) + + def _isf(self, p, c): + return sc.log1p(-np.log(p)/c) + + def _entropy(self, c): + return 1.0 - np.log(c) - sc._ufuncs._scaled_exp1(c)/c + + +gompertz = gompertz_gen(a=0.0, name='gompertz') + + +def _average_with_log_weights(x, logweights): + x = np.asarray(x) + logweights = np.asarray(logweights) + maxlogw = logweights.max() + weights = np.exp(logweights - maxlogw) + return np.average(x, weights=weights) + + +class gumbel_r_gen(rv_continuous): + r"""A right-skewed Gumbel continuous random variable. + + %(before_notes)s + + See Also + -------- + gumbel_l, gompertz, genextreme + + Notes + ----- + The probability density function for `gumbel_r` is: + + .. math:: + + f(x) = \exp(-(x + e^{-x})) + + The Gumbel distribution is sometimes referred to as a type I Fisher-Tippett + distribution. It is also related to the extreme value distribution, + log-Weibull and Gompertz distributions. + + %(after_notes)s + + %(example)s + + """ + def _shape_info(self): + return [] + + def _pdf(self, x): + # gumbel_r.pdf(x) = exp(-(x + exp(-x))) + return np.exp(self._logpdf(x)) + + def _logpdf(self, x): + return -x - np.exp(-x) + + def _cdf(self, x): + return np.exp(-np.exp(-x)) + + def _logcdf(self, x): + return -np.exp(-x) + + def _ppf(self, q): + return -np.log(-np.log(q)) + + def _sf(self, x): + return -sc.expm1(-np.exp(-x)) + + def _isf(self, p): + return -np.log(-np.log1p(-p)) + + def _stats(self): + return _EULER, np.pi*np.pi/6.0, 12*np.sqrt(6)/np.pi**3 * _ZETA3, 12.0/5 + + def _entropy(self): + # https://en.wikipedia.org/wiki/Gumbel_distribution + return _EULER + 1. + + @_call_super_mom + @inherit_docstring_from(rv_continuous) + def fit(self, data, *args, **kwds): + data, floc, fscale = _check_fit_input_parameters(self, data, + args, kwds) + + # By the method of maximum likelihood, the estimators of the + # location and scale are the roots of the equations defined in + # `func` and the value of the expression for `loc` that follows. + # The first `func` is a first order derivative of the log-likelihood + # equation and the second is from Source: Statistical Distributions, + # 3rd Edition. Evans, Hastings, and Peacock (2000), Page 101. + + def get_loc_from_scale(scale): + return -scale * (sc.logsumexp(-data / scale) - np.log(len(data))) + + if fscale is not None: + # if the scale is fixed, the location can be analytically + # determined. + scale = fscale + loc = get_loc_from_scale(scale) + else: + # A different function is solved depending on whether the location + # is fixed. + if floc is not None: + loc = floc + + # equation to use if the location is fixed. + # note that one cannot use the equation in Evans, Hastings, + # and Peacock (2000) (since it assumes that the derivative + # w.r.t. the log-likelihood is zero). however, it is easy to + # derive the MLE condition directly if loc is fixed + def func(scale): + term1 = (loc - data) * np.exp((loc - data) / scale) + data + term2 = len(data) * (loc + scale) + return term1.sum() - term2 + else: + + # equation to use if both location and scale are free + def func(scale): + sdata = -data / scale + wavg = _average_with_log_weights(data, logweights=sdata) + return data.mean() - wavg - scale + + # set brackets for `root_scalar` to use when optimizing over the + # scale such that a root is likely between them. Use user supplied + # guess or default 1. + brack_start = kwds.get('scale', 1) + lbrack, rbrack = brack_start / 2, brack_start * 2 + + # if a root is not between the brackets, iteratively expand them + # until they include a sign change, checking after each bracket is + # modified. + def interval_contains_root(lbrack, rbrack): + # return true if the signs disagree. + return (np.sign(func(lbrack)) != + np.sign(func(rbrack))) + while (not interval_contains_root(lbrack, rbrack) + and (lbrack > 0 or rbrack < np.inf)): + lbrack /= 2 + rbrack *= 2 + + res = optimize.root_scalar(func, bracket=(lbrack, rbrack), + rtol=1e-14, xtol=1e-14) + scale = res.root + loc = floc if floc is not None else get_loc_from_scale(scale) + return loc, scale + + +gumbel_r = gumbel_r_gen(name='gumbel_r') + + +class gumbel_l_gen(rv_continuous): + r"""A left-skewed Gumbel continuous random variable. + + %(before_notes)s + + See Also + -------- + gumbel_r, gompertz, genextreme + + Notes + ----- + The probability density function for `gumbel_l` is: + + .. math:: + + f(x) = \exp(x - e^x) + + The Gumbel distribution is sometimes referred to as a type I Fisher-Tippett + distribution. It is also related to the extreme value distribution, + log-Weibull and Gompertz distributions. + + %(after_notes)s + + %(example)s + + """ + + def _shape_info(self): + return [] + + def _pdf(self, x): + # gumbel_l.pdf(x) = exp(x - exp(x)) + return np.exp(self._logpdf(x)) + + def _logpdf(self, x): + return x - np.exp(x) + + def _cdf(self, x): + return -sc.expm1(-np.exp(x)) + + def _ppf(self, q): + return np.log(-sc.log1p(-q)) + + def _logsf(self, x): + return -np.exp(x) + + def _sf(self, x): + return np.exp(-np.exp(x)) + + def _isf(self, x): + return np.log(-np.log(x)) + + def _stats(self): + return -_EULER, np.pi*np.pi/6.0, \ + -12*np.sqrt(6)/np.pi**3 * _ZETA3, 12.0/5 + + def _entropy(self): + return _EULER + 1. + + @_call_super_mom + @inherit_docstring_from(rv_continuous) + def fit(self, data, *args, **kwds): + # The fit method of `gumbel_r` can be used for this distribution with + # small modifications. The process to do this is + # 1. pass the sign negated data into `gumbel_r.fit` + # - if the location is fixed, it should also be negated. + # 2. negate the sign of the resulting location, leaving the scale + # unmodified. + # `gumbel_r.fit` holds necessary input checks. + + if kwds.get('floc') is not None: + kwds['floc'] = -kwds['floc'] + loc_r, scale_r, = gumbel_r.fit(-np.asarray(data), *args, **kwds) + return -loc_r, scale_r + + +gumbel_l = gumbel_l_gen(name='gumbel_l') + + +class halfcauchy_gen(rv_continuous): + r"""A Half-Cauchy continuous random variable. + + %(before_notes)s + + Notes + ----- + The probability density function for `halfcauchy` is: + + .. math:: + + f(x) = \frac{2}{\pi (1 + x^2)} + + for :math:`x \ge 0`. + + %(after_notes)s + + %(example)s + + """ + def _shape_info(self): + return [] + + def _pdf(self, x): + # halfcauchy.pdf(x) = 2 / (pi * (1 + x**2)) + return 2.0/np.pi/(1.0+x*x) + + def _logpdf(self, x): + return np.log(2.0/np.pi) - sc.log1p(x*x) + + def _cdf(self, x): + return 2.0/np.pi*np.arctan(x) + + def _ppf(self, q): + return np.tan(np.pi/2*q) + + def _sf(self, x): + return 2.0/np.pi * np.arctan2(1, x) + + def _isf(self, p): + return 1.0/np.tan(np.pi*p/2) + + def _stats(self): + return np.inf, np.inf, np.nan, np.nan + + def _entropy(self): + return np.log(2*np.pi) + + @_call_super_mom + @inherit_docstring_from(rv_continuous) + def fit(self, data, *args, **kwds): + if kwds.pop('superfit', False): + return super().fit(data, *args, **kwds) + + data, floc, fscale = _check_fit_input_parameters(self, data, + args, kwds) + + # location is independent from the scale + data_min = np.min(data) + if floc is not None: + if data_min < floc: + # There are values that are less than the specified loc. + raise FitDataError("halfcauchy", lower=floc, upper=np.inf) + loc = floc + else: + # if not provided, location MLE is the minimal data point + loc = data_min + + # find scale + def find_scale(loc, data): + shifted_data = data - loc + n = data.size + shifted_data_squared = np.square(shifted_data) + + def fun_to_solve(scale): + denominator = scale**2 + shifted_data_squared + return 2 * np.sum(shifted_data_squared/denominator) - n + + small = np.finfo(1.0).tiny**0.5 # avoid underflow + res = root_scalar(fun_to_solve, bracket=(small, np.max(shifted_data))) + return res.root + + if fscale is not None: + scale = fscale + else: + scale = find_scale(loc, data) + + return loc, scale + + +halfcauchy = halfcauchy_gen(a=0.0, name='halfcauchy') + + +class halflogistic_gen(rv_continuous): + r"""A half-logistic continuous random variable. + + %(before_notes)s + + Notes + ----- + The probability density function for `halflogistic` is: + + .. math:: + + f(x) = \frac{ 2 e^{-x} }{ (1+e^{-x})^2 } + = \frac{1}{2} \text{sech}(x/2)^2 + + for :math:`x \ge 0`. + + %(after_notes)s + + References + ---------- + .. [1] Asgharzadeh et al (2011). "Comparisons of Methods of Estimation for the + Half-Logistic Distribution". Selcuk J. Appl. Math. 93-108. + + %(example)s + + """ + def _shape_info(self): + return [] + + def _pdf(self, x): + # halflogistic.pdf(x) = 2 * exp(-x) / (1+exp(-x))**2 + # = 1/2 * sech(x/2)**2 + return np.exp(self._logpdf(x)) + + def _logpdf(self, x): + return np.log(2) - x - 2. * sc.log1p(np.exp(-x)) + + def _cdf(self, x): + return np.tanh(x/2.0) + + def _ppf(self, q): + return 2*np.arctanh(q) + + def _sf(self, x): + return 2 * sc.expit(-x) + + def _isf(self, q): + return _lazywhere(q < 0.5, (q, ), + lambda q: -sc.logit(0.5 * q), + f2=lambda q: 2*np.arctanh(1 - q)) + + def _munp(self, n): + if n == 1: + return 2*np.log(2) + if n == 2: + return np.pi*np.pi/3.0 + if n == 3: + return 9*_ZETA3 + if n == 4: + return 7*np.pi**4 / 15.0 + return 2*(1-pow(2.0, 1-n))*sc.gamma(n+1)*sc.zeta(n, 1) + + def _entropy(self): + return 2-np.log(2) + + @_call_super_mom + @inherit_docstring_from(rv_continuous) + def fit(self, data, *args, **kwds): + if kwds.pop('superfit', False): + return super().fit(data, *args, **kwds) + + data, floc, fscale = _check_fit_input_parameters(self, data, + args, kwds) + + def find_scale(data, loc): + # scale is solution to a fix point problem ([1] 2.6) + # use approximate MLE as starting point ([1] 3.1) + n_observations = data.shape[0] + sorted_data = np.sort(data, axis=0) + p = np.arange(1, n_observations + 1)/(n_observations + 1) + q = 1 - p + pp1 = 1 + p + alpha = p - 0.5 * q * pp1 * np.log(pp1 / q) + beta = 0.5 * q * pp1 + sorted_data = sorted_data - loc + B = 2 * np.sum(alpha[1:] * sorted_data[1:]) + C = 2 * np.sum(beta[1:] * sorted_data[1:]**2) + # starting guess + scale = ((B + np.sqrt(B**2 + 8 * n_observations * C)) + /(4 * n_observations)) + + # relative tolerance of fix point iterator + rtol = 1e-8 + relative_residual = 1 + shifted_mean = sorted_data.mean() # y_mean - y_min + + # find fix point by repeated application of eq. (2.6) + # simplify as + # exp(-x) / (1 + exp(-x)) = 1 / (1 + exp(x)) + # = expit(-x)) + while relative_residual > rtol: + sum_term = sorted_data * sc.expit(-sorted_data/scale) + scale_new = shifted_mean - 2/n_observations * sum_term.sum() + relative_residual = abs((scale - scale_new)/scale) + scale = scale_new + return scale + + # location is independent from the scale + data_min = np.min(data) + if floc is not None: + if data_min < floc: + # There are values that are less than the specified loc. + raise FitDataError("halflogistic", lower=floc, upper=np.inf) + loc = floc + else: + # if not provided, location MLE is the minimal data point + loc = data_min + + # scale depends on location + scale = fscale if fscale is not None else find_scale(data, loc) + + return loc, scale + + +halflogistic = halflogistic_gen(a=0.0, name='halflogistic') + + +class halfnorm_gen(rv_continuous): + r"""A half-normal continuous random variable. + + %(before_notes)s + + Notes + ----- + The probability density function for `halfnorm` is: + + .. math:: + + f(x) = \sqrt{2/\pi} \exp(-x^2 / 2) + + for :math:`x >= 0`. + + `halfnorm` is a special case of `chi` with ``df=1``. + + %(after_notes)s + + %(example)s + + """ + def _shape_info(self): + return [] + + def _rvs(self, size=None, random_state=None): + return abs(random_state.standard_normal(size=size)) + + def _pdf(self, x): + # halfnorm.pdf(x) = sqrt(2/pi) * exp(-x**2/2) + return np.sqrt(2.0/np.pi)*np.exp(-x*x/2.0) + + def _logpdf(self, x): + return 0.5 * np.log(2.0/np.pi) - x*x/2.0 + + def _cdf(self, x): + return sc.erf(x / np.sqrt(2)) + + def _ppf(self, q): + return _norm_ppf((1+q)/2.0) + + def _sf(self, x): + return 2 * _norm_sf(x) + + def _isf(self, p): + return _norm_isf(p/2) + + def _stats(self): + return (np.sqrt(2.0/np.pi), + 1-2.0/np.pi, + np.sqrt(2)*(4-np.pi)/(np.pi-2)**1.5, + 8*(np.pi-3)/(np.pi-2)**2) + + def _entropy(self): + return 0.5*np.log(np.pi/2.0)+0.5 + + @_call_super_mom + @inherit_docstring_from(rv_continuous) + def fit(self, data, *args, **kwds): + if kwds.pop('superfit', False): + return super().fit(data, *args, **kwds) + + data, floc, fscale = _check_fit_input_parameters(self, data, + args, kwds) + + data_min = np.min(data) + + if floc is not None: + if data_min < floc: + # There are values that are less than the specified loc. + raise FitDataError("halfnorm", lower=floc, upper=np.inf) + loc = floc + else: + loc = data_min + + if fscale is not None: + scale = fscale + else: + scale = stats.moment(data, order=2, center=loc)**0.5 + + return loc, scale + + +halfnorm = halfnorm_gen(a=0.0, name='halfnorm') + + +class hypsecant_gen(rv_continuous): + r"""A hyperbolic secant continuous random variable. + + %(before_notes)s + + Notes + ----- + The probability density function for `hypsecant` is: + + .. math:: + + f(x) = \frac{1}{\pi} \text{sech}(x) + + for a real number :math:`x`. + + %(after_notes)s + + %(example)s + + """ + def _shape_info(self): + return [] + + def _pdf(self, x): + # hypsecant.pdf(x) = 1/pi * sech(x) + return 1.0/(np.pi*np.cosh(x)) + + def _cdf(self, x): + return 2.0/np.pi*np.arctan(np.exp(x)) + + def _ppf(self, q): + return np.log(np.tan(np.pi*q/2.0)) + + def _sf(self, x): + return 2.0/np.pi*np.arctan(np.exp(-x)) + + def _isf(self, q): + return -np.log(np.tan(np.pi*q/2.0)) + + def _stats(self): + return 0, np.pi*np.pi/4, 0, 2 + + def _entropy(self): + return np.log(2*np.pi) + + +hypsecant = hypsecant_gen(name='hypsecant') + + +class gausshyper_gen(rv_continuous): + r"""A Gauss hypergeometric continuous random variable. + + %(before_notes)s + + Notes + ----- + The probability density function for `gausshyper` is: + + .. math:: + + f(x, a, b, c, z) = C x^{a-1} (1-x)^{b-1} (1+zx)^{-c} + + for :math:`0 \le x \le 1`, :math:`a,b > 0`, :math:`c` a real number, + :math:`z > -1`, and :math:`C = \frac{1}{B(a, b) F[2, 1](c, a; a+b; -z)}`. + :math:`F[2, 1]` is the Gauss hypergeometric function + `scipy.special.hyp2f1`. + + `gausshyper` takes :math:`a`, :math:`b`, :math:`c` and :math:`z` as shape + parameters. + + %(after_notes)s + + References + ---------- + .. [1] Armero, C., and M. J. Bayarri. "Prior Assessments for Prediction in + Queues." *Journal of the Royal Statistical Society*. Series D (The + Statistician) 43, no. 1 (1994): 139-53. doi:10.2307/2348939 + + %(example)s + + """ + + def _argcheck(self, a, b, c, z): + # z > -1 per gh-10134 + return (a > 0) & (b > 0) & (c == c) & (z > -1) + + def _shape_info(self): + ia = _ShapeInfo("a", False, (0, np.inf), (False, False)) + ib = _ShapeInfo("b", False, (0, np.inf), (False, False)) + ic = _ShapeInfo("c", False, (-np.inf, np.inf), (False, False)) + iz = _ShapeInfo("z", False, (-1, np.inf), (False, False)) + return [ia, ib, ic, iz] + + def _pdf(self, x, a, b, c, z): + normalization_constant = sc.beta(a, b) * sc.hyp2f1(c, a, a + b, -z) + return (1./normalization_constant * x**(a - 1.) * (1. - x)**(b - 1.0) + / (1.0 + z*x)**c) + + def _munp(self, n, a, b, c, z): + fac = sc.beta(n+a, b) / sc.beta(a, b) + num = sc.hyp2f1(c, a+n, a+b+n, -z) + den = sc.hyp2f1(c, a, a+b, -z) + return fac*num / den + + +gausshyper = gausshyper_gen(a=0.0, b=1.0, name='gausshyper') + + +class invgamma_gen(rv_continuous): + r"""An inverted gamma continuous random variable. + + %(before_notes)s + + Notes + ----- + The probability density function for `invgamma` is: + + .. math:: + + f(x, a) = \frac{x^{-a-1}}{\Gamma(a)} \exp(-\frac{1}{x}) + + for :math:`x >= 0`, :math:`a > 0`. :math:`\Gamma` is the gamma function + (`scipy.special.gamma`). + + `invgamma` takes ``a`` as a shape parameter for :math:`a`. + + `invgamma` is a special case of `gengamma` with ``c=-1``, and it is a + different parameterization of the scaled inverse chi-squared distribution. + Specifically, if the scaled inverse chi-squared distribution is + parameterized with degrees of freedom :math:`\nu` and scaling parameter + :math:`\tau^2`, then it can be modeled using `invgamma` with + ``a=`` :math:`\nu/2` and ``scale=`` :math:`\nu \tau^2/2`. + + %(after_notes)s + + %(example)s + + """ + _support_mask = rv_continuous._open_support_mask + + def _shape_info(self): + return [_ShapeInfo("c", False, (0, np.inf), (False, False))] + + def _pdf(self, x, a): + # invgamma.pdf(x, a) = x**(-a-1) / gamma(a) * exp(-1/x) + return np.exp(self._logpdf(x, a)) + + def _logpdf(self, x, a): + return -(a+1) * np.log(x) - sc.gammaln(a) - 1.0/x + + def _cdf(self, x, a): + return sc.gammaincc(a, 1.0 / x) + + def _ppf(self, q, a): + return 1.0 / sc.gammainccinv(a, q) + + def _sf(self, x, a): + return sc.gammainc(a, 1.0 / x) + + def _isf(self, q, a): + return 1.0 / sc.gammaincinv(a, q) + + def _stats(self, a, moments='mvsk'): + m1 = _lazywhere(a > 1, (a,), lambda x: 1. / (x - 1.), np.inf) + m2 = _lazywhere(a > 2, (a,), lambda x: 1. / (x - 1.)**2 / (x - 2.), + np.inf) + + g1, g2 = None, None + if 's' in moments: + g1 = _lazywhere( + a > 3, (a,), + lambda x: 4. * np.sqrt(x - 2.) / (x - 3.), np.nan) + if 'k' in moments: + g2 = _lazywhere( + a > 4, (a,), + lambda x: 6. * (5. * x - 11.) / (x - 3.) / (x - 4.), np.nan) + return m1, m2, g1, g2 + + def _entropy(self, a): + def regular(a): + h = a - (a + 1.0) * sc.psi(a) + sc.gammaln(a) + return h + + def asymptotic(a): + # gammaln(a) ~ a * ln(a) - a - 0.5 * ln(a) + 0.5 * ln(2 * pi) + # psi(a) ~ ln(a) - 1 / (2 * a) + h = ((1 - 3*np.log(a) + np.log(2) + np.log(np.pi))/2 + + 2/3*a**-1. + a**-2./12 - a**-3./90 - a**-4./120) + return h + + h = _lazywhere(a >= 2e2, (a,), f=asymptotic, f2=regular) + return h + + +invgamma = invgamma_gen(a=0.0, name='invgamma') + + +class invgauss_gen(rv_continuous): + r"""An inverse Gaussian continuous random variable. + + %(before_notes)s + + Notes + ----- + The probability density function for `invgauss` is: + + .. math:: + + f(x; \mu) = \frac{1}{\sqrt{2 \pi x^3}} + \exp\left(-\frac{(x-\mu)^2}{2 \mu^2 x}\right) + + for :math:`x \ge 0` and :math:`\mu > 0`. + + `invgauss` takes ``mu`` as a shape parameter for :math:`\mu`. + + %(after_notes)s + + A common shape-scale parameterization of the inverse Gaussian distribution + has density + + .. math:: + + f(x; \nu, \lambda) = \sqrt{\frac{\lambda}{2 \pi x^3}} + \exp\left( -\frac{\lambda(x-\nu)^2}{2 \nu^2 x}\right) + + Using ``nu`` for :math:`\nu` and ``lam`` for :math:`\lambda`, this + parameterization is equivalent to the one above with ``mu = nu/lam``, + ``loc = 0``, and ``scale = lam``. + + %(example)s + + """ + _support_mask = rv_continuous._open_support_mask + + def _shape_info(self): + return [_ShapeInfo("mu", False, (0, np.inf), (False, False))] + + def _rvs(self, mu, size=None, random_state=None): + return random_state.wald(mu, 1.0, size=size) + + def _pdf(self, x, mu): + # invgauss.pdf(x, mu) = + # 1 / sqrt(2*pi*x**3) * exp(-(x-mu)**2/(2*x*mu**2)) + return 1.0/np.sqrt(2*np.pi*x**3.0)*np.exp(-1.0/(2*x)*((x-mu)/mu)**2) + + def _logpdf(self, x, mu): + return -0.5*np.log(2*np.pi) - 1.5*np.log(x) - ((x-mu)/mu)**2/(2*x) + + # approach adapted from equations in + # https://journal.r-project.org/archive/2016-1/giner-smyth.pdf, + # not R code. see gh-13616 + + def _logcdf(self, x, mu): + fac = 1 / np.sqrt(x) + a = _norm_logcdf(fac * ((x / mu) - 1)) + b = 2 / mu + _norm_logcdf(-fac * ((x / mu) + 1)) + return a + np.log1p(np.exp(b - a)) + + def _logsf(self, x, mu): + fac = 1 / np.sqrt(x) + a = _norm_logsf(fac * ((x / mu) - 1)) + b = 2 / mu + _norm_logcdf(-fac * (x + mu) / mu) + return a + np.log1p(-np.exp(b - a)) + + def _sf(self, x, mu): + return np.exp(self._logsf(x, mu)) + + def _cdf(self, x, mu): + return np.exp(self._logcdf(x, mu)) + + def _ppf(self, x, mu): + with np.errstate(divide='ignore', over='ignore', invalid='ignore'): + x, mu = np.broadcast_arrays(x, mu) + ppf = _boost._invgauss_ppf(x, mu, 1) + i_wt = x > 0.5 # "wrong tail" - sometimes too inaccurate + ppf[i_wt] = _boost._invgauss_isf(1-x[i_wt], mu[i_wt], 1) + i_nan = np.isnan(ppf) + ppf[i_nan] = super()._ppf(x[i_nan], mu[i_nan]) + return ppf + + def _isf(self, x, mu): + with np.errstate(divide='ignore', over='ignore', invalid='ignore'): + x, mu = np.broadcast_arrays(x, mu) + isf = _boost._invgauss_isf(x, mu, 1) + i_wt = x > 0.5 # "wrong tail" - sometimes too inaccurate + isf[i_wt] = _boost._invgauss_ppf(1-x[i_wt], mu[i_wt], 1) + i_nan = np.isnan(isf) + isf[i_nan] = super()._isf(x[i_nan], mu[i_nan]) + return isf + + def _stats(self, mu): + return mu, mu**3.0, 3*np.sqrt(mu), 15*mu + + @inherit_docstring_from(rv_continuous) + def fit(self, data, *args, **kwds): + method = kwds.get('method', 'mle') + + if (isinstance(data, CensoredData) or type(self) == wald_gen + or method.lower() == 'mm'): + return super().fit(data, *args, **kwds) + + data, fshape_s, floc, fscale = _check_fit_input_parameters(self, data, + args, kwds) + ''' + Source: Statistical Distributions, 3rd Edition. Evans, Hastings, + and Peacock (2000), Page 121. Their shape parameter is equivalent to + SciPy's with the conversion `fshape_s = fshape / scale`. + + MLE formulas are not used in 3 conditions: + - `loc` is not fixed + - `mu` is fixed + These cases fall back on the superclass fit method. + - `loc` is fixed but translation results in negative data raises + a `FitDataError`. + ''' + if floc is None or fshape_s is not None: + return super().fit(data, *args, **kwds) + elif np.any(data - floc < 0): + raise FitDataError("invgauss", lower=0, upper=np.inf) + else: + data = data - floc + fshape_n = np.mean(data) + if fscale is None: + fscale = len(data) / (np.sum(data ** -1 - fshape_n ** -1)) + fshape_s = fshape_n / fscale + return fshape_s, floc, fscale + + def _entropy(self, mu): + """ + Ref.: https://moser-isi.ethz.ch/docs/papers/smos-2012-10.pdf (eq. 9) + """ + # a = log(2*pi*e*mu**3) + # = 1 + log(2*pi) + 3 * log(mu) + a = 1. + np.log(2 * np.pi) + 3 * np.log(mu) + # b = exp(2/mu) * exp1(2/mu) + # = _scaled_exp1(2/mu) / (2/mu) + r = 2/mu + b = sc._ufuncs._scaled_exp1(r)/r + return 0.5 * a - 1.5 * b + + +invgauss = invgauss_gen(a=0.0, name='invgauss') + + +class geninvgauss_gen(rv_continuous): + r"""A Generalized Inverse Gaussian continuous random variable. + + %(before_notes)s + + Notes + ----- + The probability density function for `geninvgauss` is: + + .. math:: + + f(x, p, b) = x^{p-1} \exp(-b (x + 1/x) / 2) / (2 K_p(b)) + + where `x > 0`, `p` is a real number and `b > 0`\([1]_). + :math:`K_p` is the modified Bessel function of second kind of order `p` + (`scipy.special.kv`). + + %(after_notes)s + + The inverse Gaussian distribution `stats.invgauss(mu)` is a special case of + `geninvgauss` with `p = -1/2`, `b = 1 / mu` and `scale = mu`. + + Generating random variates is challenging for this distribution. The + implementation is based on [2]_. + + References + ---------- + .. [1] O. Barndorff-Nielsen, P. Blaesild, C. Halgreen, "First hitting time + models for the generalized inverse gaussian distribution", + Stochastic Processes and their Applications 7, pp. 49--54, 1978. + + .. [2] W. Hoermann and J. Leydold, "Generating generalized inverse Gaussian + random variates", Statistics and Computing, 24(4), p. 547--557, 2014. + + %(example)s + + """ + def _argcheck(self, p, b): + return (p == p) & (b > 0) + + def _shape_info(self): + ip = _ShapeInfo("p", False, (-np.inf, np.inf), (False, False)) + ib = _ShapeInfo("b", False, (0, np.inf), (False, False)) + return [ip, ib] + + def _logpdf(self, x, p, b): + # kve instead of kv works better for large values of b + # warn if kve produces infinite values and replace by nan + # otherwise c = -inf and the results are often incorrect + def logpdf_single(x, p, b): + return _stats.geninvgauss_logpdf(x, p, b) + + logpdf_single = np.vectorize(logpdf_single, otypes=[np.float64]) + + z = logpdf_single(x, p, b) + if np.isnan(z).any(): + msg = ("Infinite values encountered in scipy.special.kve(p, b). " + "Values replaced by NaN to avoid incorrect results.") + warnings.warn(msg, RuntimeWarning, stacklevel=3) + return z + + def _pdf(self, x, p, b): + # relying on logpdf avoids overflow of x**(p-1) for large x and p + return np.exp(self._logpdf(x, p, b)) + + def _cdf(self, x, *args): + _a, _b = self._get_support(*args) + + def _cdf_single(x, *args): + p, b = args + user_data = np.array([p, b], float).ctypes.data_as(ctypes.c_void_p) + llc = LowLevelCallable.from_cython(_stats, '_geninvgauss_pdf', + user_data) + + return integrate.quad(llc, _a, x)[0] + + _cdf_single = np.vectorize(_cdf_single, otypes=[np.float64]) + + return _cdf_single(x, *args) + + def _logquasipdf(self, x, p, b): + # log of the quasi-density (w/o normalizing constant) used in _rvs + return _lazywhere(x > 0, (x, p, b), + lambda x, p, b: (p - 1)*np.log(x) - b*(x + 1/x)/2, + -np.inf) + + def _rvs(self, p, b, size=None, random_state=None): + # if p and b are scalar, use _rvs_scalar, otherwise need to create + # output by iterating over parameters + if np.isscalar(p) and np.isscalar(b): + out = self._rvs_scalar(p, b, size, random_state) + elif p.size == 1 and b.size == 1: + out = self._rvs_scalar(p.item(), b.item(), size, random_state) + else: + # When this method is called, size will be a (possibly empty) + # tuple of integers. It will not be None; if `size=None` is passed + # to `rvs()`, size will be the empty tuple (). + + p, b = np.broadcast_arrays(p, b) + # p and b now have the same shape. + + # `shp` is the shape of the blocks of random variates that are + # generated for each combination of parameters associated with + # broadcasting p and b. + # bc is a tuple the same length as size. The values + # in bc are bools. If bc[j] is True, it means that + # entire axis is filled in for a given combination of the + # broadcast arguments. + shp, bc = _check_shape(p.shape, size) + + # `numsamples` is the total number of variates to be generated + # for each combination of the input arguments. + numsamples = int(np.prod(shp)) + + # `out` is the array to be returned. It is filled in the + # loop below. + out = np.empty(size) + + it = np.nditer([p, b], + flags=['multi_index'], + op_flags=[['readonly'], ['readonly']]) + while not it.finished: + # Convert the iterator's multi_index into an index into the + # `out` array where the call to _rvs_scalar() will be stored. + # Where bc is True, we use a full slice; otherwise we use the + # index value from it.multi_index. len(it.multi_index) might + # be less than len(bc), and in that case we want to align these + # two sequences to the right, so the loop variable j runs from + # -len(size) to 0. This doesn't cause an IndexError, as + # bc[j] will be True in those cases where it.multi_index[j] + # would cause an IndexError. + idx = tuple((it.multi_index[j] if not bc[j] else slice(None)) + for j in range(-len(size), 0)) + out[idx] = self._rvs_scalar(it[0], it[1], numsamples, + random_state).reshape(shp) + it.iternext() + + if size == (): + out = out.item() + return out + + def _rvs_scalar(self, p, b, numsamples, random_state): + # following [2], the quasi-pdf is used instead of the pdf for the + # generation of rvs + invert_res = False + if not numsamples: + numsamples = 1 + if p < 0: + # note: if X is geninvgauss(p, b), then 1/X is geninvgauss(-p, b) + p = -p + invert_res = True + m = self._mode(p, b) + + # determine method to be used following [2] + ratio_unif = True + if p >= 1 or b > 1: + # ratio of uniforms with mode shift below + mode_shift = True + elif b >= min(0.5, 2 * np.sqrt(1 - p) / 3): + # ratio of uniforms without mode shift below + mode_shift = False + else: + # new algorithm in [2] + ratio_unif = False + + # prepare sampling of rvs + size1d = tuple(np.atleast_1d(numsamples)) + N = np.prod(size1d) # number of rvs needed, reshape upon return + x = np.zeros(N) + simulated = 0 + + if ratio_unif: + # use ratio of uniforms method + if mode_shift: + a2 = -2 * (p + 1) / b - m + a1 = 2 * m * (p - 1) / b - 1 + # find roots of x**3 + a2*x**2 + a1*x + m (Cardano's formula) + p1 = a1 - a2**2 / 3 + q1 = 2 * a2**3 / 27 - a2 * a1 / 3 + m + phi = np.arccos(-q1 * np.sqrt(-27 / p1**3) / 2) + s1 = -np.sqrt(-4 * p1 / 3) + root1 = s1 * np.cos(phi / 3 + np.pi / 3) - a2 / 3 + root2 = -s1 * np.cos(phi / 3) - a2 / 3 + # root3 = s1 * np.cos(phi / 3 - np.pi / 3) - a2 / 3 + + # if g is the quasipdf, rescale: g(x) / g(m) which we can write + # as exp(log(g(x)) - log(g(m))). This is important + # since for large values of p and b, g cannot be evaluated. + # denote the rescaled quasipdf by h + lm = self._logquasipdf(m, p, b) + d1 = self._logquasipdf(root1, p, b) - lm + d2 = self._logquasipdf(root2, p, b) - lm + # compute the bounding rectangle w.r.t. h. Note that + # np.exp(0.5*d1) = np.sqrt(g(root1)/g(m)) = np.sqrt(h(root1)) + vmin = (root1 - m) * np.exp(0.5 * d1) + vmax = (root2 - m) * np.exp(0.5 * d2) + umax = 1 # umax = sqrt(h(m)) = 1 + + def logqpdf(x): + return self._logquasipdf(x, p, b) - lm + + c = m + else: + # ratio of uniforms without mode shift + # compute np.sqrt(quasipdf(m)) + umax = np.exp(0.5*self._logquasipdf(m, p, b)) + xplus = ((1 + p) + np.sqrt((1 + p)**2 + b**2))/b + vmin = 0 + # compute xplus * np.sqrt(quasipdf(xplus)) + vmax = xplus * np.exp(0.5 * self._logquasipdf(xplus, p, b)) + c = 0 + + def logqpdf(x): + return self._logquasipdf(x, p, b) + + if vmin >= vmax: + raise ValueError("vmin must be smaller than vmax.") + if umax <= 0: + raise ValueError("umax must be positive.") + + i = 1 + while simulated < N: + k = N - simulated + # simulate uniform rvs on [0, umax] and [vmin, vmax] + u = umax * random_state.uniform(size=k) + v = random_state.uniform(size=k) + v = vmin + (vmax - vmin) * v + rvs = v / u + c + # rewrite acceptance condition u**2 <= pdf(rvs) by taking logs + accept = (2*np.log(u) <= logqpdf(rvs)) + num_accept = np.sum(accept) + if num_accept > 0: + x[simulated:(simulated + num_accept)] = rvs[accept] + simulated += num_accept + + if (simulated == 0) and (i*N >= 50000): + msg = ("Not a single random variate could be generated " + f"in {i*N} attempts. Sampling does not appear to " + "work for the provided parameters.") + raise RuntimeError(msg) + i += 1 + else: + # use new algorithm in [2] + x0 = b / (1 - p) + xs = np.max((x0, 2 / b)) + k1 = np.exp(self._logquasipdf(m, p, b)) + A1 = k1 * x0 + if x0 < 2 / b: + k2 = np.exp(-b) + if p > 0: + A2 = k2 * ((2 / b)**p - x0**p) / p + else: + A2 = k2 * np.log(2 / b**2) + else: + k2, A2 = 0, 0 + k3 = xs**(p - 1) + A3 = 2 * k3 * np.exp(-xs * b / 2) / b + A = A1 + A2 + A3 + + # [2]: rejection constant is < 2.73; so expected runtime is finite + while simulated < N: + k = N - simulated + h, rvs = np.zeros(k), np.zeros(k) + # simulate uniform rvs on [x1, x2] and [0, y2] + u = random_state.uniform(size=k) + v = A * random_state.uniform(size=k) + cond1 = v <= A1 + cond2 = np.logical_not(cond1) & (v <= A1 + A2) + cond3 = np.logical_not(cond1 | cond2) + # subdomain (0, x0) + rvs[cond1] = x0 * v[cond1] / A1 + h[cond1] = k1 + # subdomain (x0, 2 / b) + if p > 0: + rvs[cond2] = (x0**p + (v[cond2] - A1) * p / k2)**(1 / p) + else: + rvs[cond2] = b * np.exp((v[cond2] - A1) * np.exp(b)) + h[cond2] = k2 * rvs[cond2]**(p - 1) + # subdomain (xs, infinity) + z = np.exp(-xs * b / 2) - b * (v[cond3] - A1 - A2) / (2 * k3) + rvs[cond3] = -2 / b * np.log(z) + h[cond3] = k3 * np.exp(-rvs[cond3] * b / 2) + # apply rejection method + accept = (np.log(u * h) <= self._logquasipdf(rvs, p, b)) + num_accept = sum(accept) + if num_accept > 0: + x[simulated:(simulated + num_accept)] = rvs[accept] + simulated += num_accept + + rvs = np.reshape(x, size1d) + if invert_res: + rvs = 1 / rvs + return rvs + + def _mode(self, p, b): + # distinguish cases to avoid catastrophic cancellation (see [2]) + if p < 1: + return b / (np.sqrt((p - 1)**2 + b**2) + 1 - p) + else: + return (np.sqrt((1 - p)**2 + b**2) - (1 - p)) / b + + def _munp(self, n, p, b): + num = sc.kve(p + n, b) + denom = sc.kve(p, b) + inf_vals = np.isinf(num) | np.isinf(denom) + if inf_vals.any(): + msg = ("Infinite values encountered in the moment calculation " + "involving scipy.special.kve. Values replaced by NaN to " + "avoid incorrect results.") + warnings.warn(msg, RuntimeWarning, stacklevel=3) + m = np.full_like(num, np.nan, dtype=np.float64) + m[~inf_vals] = num[~inf_vals] / denom[~inf_vals] + else: + m = num / denom + return m + + +geninvgauss = geninvgauss_gen(a=0.0, name="geninvgauss") + + +class norminvgauss_gen(rv_continuous): + r"""A Normal Inverse Gaussian continuous random variable. + + %(before_notes)s + + Notes + ----- + The probability density function for `norminvgauss` is: + + .. math:: + + f(x, a, b) = \frac{a \, K_1(a \sqrt{1 + x^2})}{\pi \sqrt{1 + x^2}} \, + \exp(\sqrt{a^2 - b^2} + b x) + + where :math:`x` is a real number, the parameter :math:`a` is the tail + heaviness and :math:`b` is the asymmetry parameter satisfying + :math:`a > 0` and :math:`|b| <= a`. + :math:`K_1` is the modified Bessel function of second kind + (`scipy.special.k1`). + + %(after_notes)s + + A normal inverse Gaussian random variable `Y` with parameters `a` and `b` + can be expressed as a normal mean-variance mixture: + `Y = b * V + sqrt(V) * X` where `X` is `norm(0,1)` and `V` is + `invgauss(mu=1/sqrt(a**2 - b**2))`. This representation is used + to generate random variates. + + Another common parametrization of the distribution (see Equation 2.1 in + [2]_) is given by the following expression of the pdf: + + .. math:: + + g(x, \alpha, \beta, \delta, \mu) = + \frac{\alpha\delta K_1\left(\alpha\sqrt{\delta^2 + (x - \mu)^2}\right)} + {\pi \sqrt{\delta^2 + (x - \mu)^2}} \, + e^{\delta \sqrt{\alpha^2 - \beta^2} + \beta (x - \mu)} + + In SciPy, this corresponds to + `a = alpha * delta, b = beta * delta, loc = mu, scale=delta`. + + References + ---------- + .. [1] O. Barndorff-Nielsen, "Hyperbolic Distributions and Distributions on + Hyperbolae", Scandinavian Journal of Statistics, Vol. 5(3), + pp. 151-157, 1978. + + .. [2] O. Barndorff-Nielsen, "Normal Inverse Gaussian Distributions and + Stochastic Volatility Modelling", Scandinavian Journal of + Statistics, Vol. 24, pp. 1-13, 1997. + + %(example)s + + """ + _support_mask = rv_continuous._open_support_mask + + def _argcheck(self, a, b): + return (a > 0) & (np.absolute(b) < a) + + def _shape_info(self): + ia = _ShapeInfo("a", False, (0, np.inf), (False, False)) + ib = _ShapeInfo("b", False, (-np.inf, np.inf), (False, False)) + return [ia, ib] + + def _fitstart(self, data): + # Arbitrary, but the default a = b = 1 is not valid; the distribution + # requires |b| < a. + return super()._fitstart(data, args=(1, 0.5)) + + def _pdf(self, x, a, b): + gamma = np.sqrt(a**2 - b**2) + fac1 = a / np.pi + sq = np.hypot(1, x) # reduce overflows + return fac1 * sc.k1e(a * sq) * np.exp(b*x - a*sq + gamma) / sq + + def _sf(self, x, a, b): + if np.isscalar(x): + # If x is a scalar, then so are a and b. + return integrate.quad(self._pdf, x, np.inf, args=(a, b))[0] + else: + a = np.atleast_1d(a) + b = np.atleast_1d(b) + result = [] + for (x0, a0, b0) in zip(x, a, b): + result.append(integrate.quad(self._pdf, x0, np.inf, + args=(a0, b0))[0]) + return np.array(result) + + def _isf(self, q, a, b): + def _isf_scalar(q, a, b): + + def eq(x, a, b, q): + # Solve eq(x, a, b, q) = 0 to obtain isf(x, a, b) = q. + return self._sf(x, a, b) - q + + # Find a bracketing interval for the root. + # Start at the mean, and grow the length of the interval + # by 2 each iteration until there is a sign change in eq. + xm = self.mean(a, b) + em = eq(xm, a, b, q) + if em == 0: + # Unlikely, but might as well check. + return xm + if em > 0: + delta = 1 + left = xm + right = xm + delta + while eq(right, a, b, q) > 0: + delta = 2*delta + right = xm + delta + else: + # em < 0 + delta = 1 + right = xm + left = xm - delta + while eq(left, a, b, q) < 0: + delta = 2*delta + left = xm - delta + result = optimize.brentq(eq, left, right, args=(a, b, q), + xtol=self.xtol) + return result + + if np.isscalar(q): + return _isf_scalar(q, a, b) + else: + result = [] + for (q0, a0, b0) in zip(q, a, b): + result.append(_isf_scalar(q0, a0, b0)) + return np.array(result) + + def _rvs(self, a, b, size=None, random_state=None): + # note: X = b * V + sqrt(V) * X is norminvgaus(a,b) if X is standard + # normal and V is invgauss(mu=1/sqrt(a**2 - b**2)) + gamma = np.sqrt(a**2 - b**2) + ig = invgauss.rvs(mu=1/gamma, size=size, random_state=random_state) + return b * ig + np.sqrt(ig) * norm.rvs(size=size, + random_state=random_state) + + def _stats(self, a, b): + gamma = np.sqrt(a**2 - b**2) + mean = b / gamma + variance = a**2 / gamma**3 + skewness = 3.0 * b / (a * np.sqrt(gamma)) + kurtosis = 3.0 * (1 + 4 * b**2 / a**2) / gamma + return mean, variance, skewness, kurtosis + + +norminvgauss = norminvgauss_gen(name="norminvgauss") + + +class invweibull_gen(rv_continuous): + """An inverted Weibull continuous random variable. + + This distribution is also known as the Fréchet distribution or the + type II extreme value distribution. + + %(before_notes)s + + Notes + ----- + The probability density function for `invweibull` is: + + .. math:: + + f(x, c) = c x^{-c-1} \\exp(-x^{-c}) + + for :math:`x > 0`, :math:`c > 0`. + + `invweibull` takes ``c`` as a shape parameter for :math:`c`. + + %(after_notes)s + + References + ---------- + F.R.S. de Gusmao, E.M.M Ortega and G.M. Cordeiro, "The generalized inverse + Weibull distribution", Stat. Papers, vol. 52, pp. 591-619, 2011. + + %(example)s + + """ + _support_mask = rv_continuous._open_support_mask + + def _shape_info(self): + return [_ShapeInfo("c", False, (0, np.inf), (False, False))] + + def _pdf(self, x, c): + # invweibull.pdf(x, c) = c * x**(-c-1) * exp(-x**(-c)) + xc1 = np.power(x, -c - 1.0) + xc2 = np.power(x, -c) + xc2 = np.exp(-xc2) + return c * xc1 * xc2 + + def _cdf(self, x, c): + xc1 = np.power(x, -c) + return np.exp(-xc1) + + def _sf(self, x, c): + return -np.expm1(-x**-c) + + def _ppf(self, q, c): + return np.power(-np.log(q), -1.0/c) + + def _isf(self, p, c): + return (-np.log1p(-p))**(-1/c) + + def _munp(self, n, c): + return sc.gamma(1 - n / c) + + def _entropy(self, c): + return 1+_EULER + _EULER / c - np.log(c) + + def _fitstart(self, data, args=None): + # invweibull requires c > 1 for the first moment to exist, so use 2.0 + args = (2.0,) if args is None else args + return super()._fitstart(data, args=args) + + +invweibull = invweibull_gen(a=0, name='invweibull') + + +class jf_skew_t_gen(rv_continuous): + r"""Jones and Faddy skew-t distribution. + + %(before_notes)s + + Notes + ----- + The probability density function for `jf_skew_t` is: + + .. math:: + + f(x; a, b) = C_{a,b}^{-1} + \left(1+\frac{x}{\left(a+b+x^2\right)^{1/2}}\right)^{a+1/2} + \left(1-\frac{x}{\left(a+b+x^2\right)^{1/2}}\right)^{b+1/2} + + for real numbers :math:`a>0` and :math:`b>0`, where + :math:`C_{a,b} = 2^{a+b-1}B(a,b)(a+b)^{1/2}`, and :math:`B` denotes the + beta function (`scipy.special.beta`). + + When :math:`ab`, the distribution is positively skewed. If :math:`a=b`, then + we recover the `t` distribution with :math:`2a` degrees of freedom. + + `jf_skew_t` takes :math:`a` and :math:`b` as shape parameters. + + %(after_notes)s + + References + ---------- + .. [1] M.C. Jones and M.J. Faddy. "A skew extension of the t distribution, + with applications" *Journal of the Royal Statistical Society*. + Series B (Statistical Methodology) 65, no. 1 (2003): 159-174. + :doi:`10.1111/1467-9868.00378` + + %(example)s + + """ + def _shape_info(self): + ia = _ShapeInfo("a", False, (0, np.inf), (False, False)) + ib = _ShapeInfo("b", False, (0, np.inf), (False, False)) + return [ia, ib] + + def _pdf(self, x, a, b): + c = 2 ** (a + b - 1) * sc.beta(a, b) * np.sqrt(a + b) + d1 = (1 + x / np.sqrt(a + b + x ** 2)) ** (a + 0.5) + d2 = (1 - x / np.sqrt(a + b + x ** 2)) ** (b + 0.5) + return d1 * d2 / c + + def _rvs(self, a, b, size=None, random_state=None): + d1 = random_state.beta(a, b, size) + d2 = (2 * d1 - 1) * np.sqrt(a + b) + d3 = 2 * np.sqrt(d1 * (1 - d1)) + return d2 / d3 + + def _cdf(self, x, a, b): + y = (1 + x / np.sqrt(a + b + x ** 2)) * 0.5 + return sc.betainc(a, b, y) + + def _ppf(self, q, a, b): + d1 = beta.ppf(q, a, b) + d2 = (2 * d1 - 1) * np.sqrt(a + b) + d3 = 2 * np.sqrt(d1 * (1 - d1)) + return d2 / d3 + + def _munp(self, n, a, b): + """Returns the n-th moment(s) where all the following hold: + + - n >= 0 + - a > n / 2 + - b > n / 2 + + The result is np.nan in all other cases. + """ + def nth_moment(n_k, a_k, b_k): + """Computes E[T^(n_k)] where T is skew-t distributed with + parameters a_k and b_k. + """ + num = (a_k + b_k) ** (0.5 * n_k) + denom = 2 ** n_k * sc.beta(a_k, b_k) + + indices = np.arange(n_k + 1) + sgn = np.where(indices % 2 > 0, -1, 1) + d = sc.beta(a_k + 0.5 * n_k - indices, b_k - 0.5 * n_k + indices) + sum_terms = sc.comb(n_k, indices) * sgn * d + + return num / denom * sum_terms.sum() + + nth_moment_valid = (a > 0.5 * n) & (b > 0.5 * n) & (n >= 0) + return _lazywhere( + nth_moment_valid, + (n, a, b), + np.vectorize(nth_moment, otypes=[np.float64]), + np.nan, + ) + + +jf_skew_t = jf_skew_t_gen(name='jf_skew_t') + + +class johnsonsb_gen(rv_continuous): + r"""A Johnson SB continuous random variable. + + %(before_notes)s + + See Also + -------- + johnsonsu + + Notes + ----- + The probability density function for `johnsonsb` is: + + .. math:: + + f(x, a, b) = \frac{b}{x(1-x)} \phi(a + b \log \frac{x}{1-x} ) + + where :math:`x`, :math:`a`, and :math:`b` are real scalars; :math:`b > 0` + and :math:`x \in [0,1]`. :math:`\phi` is the pdf of the normal + distribution. + + `johnsonsb` takes :math:`a` and :math:`b` as shape parameters. + + %(after_notes)s + + %(example)s + + """ + _support_mask = rv_continuous._open_support_mask + + def _argcheck(self, a, b): + return (b > 0) & (a == a) + + def _shape_info(self): + ia = _ShapeInfo("a", False, (-np.inf, np.inf), (False, False)) + ib = _ShapeInfo("b", False, (0, np.inf), (False, False)) + return [ia, ib] + + def _pdf(self, x, a, b): + # johnsonsb.pdf(x, a, b) = b / (x*(1-x)) * phi(a + b * log(x/(1-x))) + trm = _norm_pdf(a + b*sc.logit(x)) + return b*1.0/(x*(1-x))*trm + + def _cdf(self, x, a, b): + return _norm_cdf(a + b*sc.logit(x)) + + def _ppf(self, q, a, b): + return sc.expit(1.0 / b * (_norm_ppf(q) - a)) + + def _sf(self, x, a, b): + return _norm_sf(a + b*sc.logit(x)) + + def _isf(self, q, a, b): + return sc.expit(1.0 / b * (_norm_isf(q) - a)) + + +johnsonsb = johnsonsb_gen(a=0.0, b=1.0, name='johnsonsb') + + +class johnsonsu_gen(rv_continuous): + r"""A Johnson SU continuous random variable. + + %(before_notes)s + + See Also + -------- + johnsonsb + + Notes + ----- + The probability density function for `johnsonsu` is: + + .. math:: + + f(x, a, b) = \frac{b}{\sqrt{x^2 + 1}} + \phi(a + b \log(x + \sqrt{x^2 + 1})) + + where :math:`x`, :math:`a`, and :math:`b` are real scalars; :math:`b > 0`. + :math:`\phi` is the pdf of the normal distribution. + + `johnsonsu` takes :math:`a` and :math:`b` as shape parameters. + + The first four central moments are calculated according to the formulas + in [1]_. + + %(after_notes)s + + References + ---------- + .. [1] Taylor Enterprises. "Johnson Family of Distributions". + https://variation.com/wp-content/distribution_analyzer_help/hs126.htm + + %(example)s + + """ + def _argcheck(self, a, b): + return (b > 0) & (a == a) + + def _shape_info(self): + ia = _ShapeInfo("a", False, (-np.inf, np.inf), (False, False)) + ib = _ShapeInfo("b", False, (0, np.inf), (False, False)) + return [ia, ib] + + def _pdf(self, x, a, b): + # johnsonsu.pdf(x, a, b) = b / sqrt(x**2 + 1) * + # phi(a + b * log(x + sqrt(x**2 + 1))) + x2 = x*x + trm = _norm_pdf(a + b * np.arcsinh(x)) + return b*1.0/np.sqrt(x2+1.0)*trm + + def _cdf(self, x, a, b): + return _norm_cdf(a + b * np.arcsinh(x)) + + def _ppf(self, q, a, b): + return np.sinh((_norm_ppf(q) - a) / b) + + def _sf(self, x, a, b): + return _norm_sf(a + b * np.arcsinh(x)) + + def _isf(self, x, a, b): + return np.sinh((_norm_isf(x) - a) / b) + + def _stats(self, a, b, moments='mv'): + # Naive implementation of first and second moment to address gh-18071. + # https://variation.com/wp-content/distribution_analyzer_help/hs126.htm + # Numerical improvements left to future enhancements. + mu, mu2, g1, g2 = None, None, None, None + + bn2 = b**-2. + expbn2 = np.exp(bn2) + a_b = a / b + + if 'm' in moments: + mu = -expbn2**0.5 * np.sinh(a_b) + if 'v' in moments: + mu2 = 0.5*sc.expm1(bn2)*(expbn2*np.cosh(2*a_b) + 1) + if 's' in moments: + t1 = expbn2**.5 * sc.expm1(bn2)**0.5 + t2 = 3*np.sinh(a_b) + t3 = expbn2 * (expbn2 + 2) * np.sinh(3*a_b) + denom = np.sqrt(2) * (1 + expbn2 * np.cosh(2*a_b))**(3/2) + g1 = -t1 * (t2 + t3) / denom + if 'k' in moments: + t1 = 3 + 6*expbn2 + t2 = 4*expbn2**2 * (expbn2 + 2) * np.cosh(2*a_b) + t3 = expbn2**2 * np.cosh(4*a_b) + t4 = -3 + 3*expbn2**2 + 2*expbn2**3 + expbn2**4 + denom = 2*(1 + expbn2*np.cosh(2*a_b))**2 + g2 = (t1 + t2 + t3*t4) / denom - 3 + return mu, mu2, g1, g2 + + +johnsonsu = johnsonsu_gen(name='johnsonsu') + + +class laplace_gen(rv_continuous): + r"""A Laplace continuous random variable. + + %(before_notes)s + + Notes + ----- + The probability density function for `laplace` is + + .. math:: + + f(x) = \frac{1}{2} \exp(-|x|) + + for a real number :math:`x`. + + %(after_notes)s + + %(example)s + + """ + def _shape_info(self): + return [] + + def _rvs(self, size=None, random_state=None): + return random_state.laplace(0, 1, size=size) + + def _pdf(self, x): + # laplace.pdf(x) = 1/2 * exp(-abs(x)) + return 0.5*np.exp(-abs(x)) + + def _cdf(self, x): + with np.errstate(over='ignore'): + return np.where(x > 0, 1.0 - 0.5*np.exp(-x), 0.5*np.exp(x)) + + def _sf(self, x): + # By symmetry... + return self._cdf(-x) + + def _ppf(self, q): + return np.where(q > 0.5, -np.log(2*(1-q)), np.log(2*q)) + + def _isf(self, q): + # By symmetry... + return -self._ppf(q) + + def _stats(self): + return 0, 2, 0, 3 + + def _entropy(self): + return np.log(2)+1 + + @_call_super_mom + @replace_notes_in_docstring(rv_continuous, notes="""\ + This function uses explicit formulas for the maximum likelihood + estimation of the Laplace distribution parameters, so the keyword + arguments `loc`, `scale`, and `optimizer` are ignored.\n\n""") + def fit(self, data, *args, **kwds): + data, floc, fscale = _check_fit_input_parameters(self, data, + args, kwds) + + # Source: Statistical Distributions, 3rd Edition. Evans, Hastings, + # and Peacock (2000), Page 124 + + if floc is None: + floc = np.median(data) + + if fscale is None: + fscale = (np.sum(np.abs(data - floc))) / len(data) + + return floc, fscale + + +laplace = laplace_gen(name='laplace') + + +class laplace_asymmetric_gen(rv_continuous): + r"""An asymmetric Laplace continuous random variable. + + %(before_notes)s + + See Also + -------- + laplace : Laplace distribution + + Notes + ----- + The probability density function for `laplace_asymmetric` is + + .. math:: + + f(x, \kappa) &= \frac{1}{\kappa+\kappa^{-1}}\exp(-x\kappa),\quad x\ge0\\ + &= \frac{1}{\kappa+\kappa^{-1}}\exp(x/\kappa),\quad x<0\\ + + for :math:`-\infty < x < \infty`, :math:`\kappa > 0`. + + `laplace_asymmetric` takes ``kappa`` as a shape parameter for + :math:`\kappa`. For :math:`\kappa = 1`, it is identical to a + Laplace distribution. + + %(after_notes)s + + Note that the scale parameter of some references is the reciprocal of + SciPy's ``scale``. For example, :math:`\lambda = 1/2` in the + parameterization of [1]_ is equivalent to ``scale = 2`` with + `laplace_asymmetric`. + + References + ---------- + .. [1] "Asymmetric Laplace distribution", Wikipedia + https://en.wikipedia.org/wiki/Asymmetric_Laplace_distribution + + .. [2] Kozubowski TJ and Podgórski K. A Multivariate and + Asymmetric Generalization of Laplace Distribution, + Computational Statistics 15, 531--540 (2000). + :doi:`10.1007/PL00022717` + + %(example)s + + """ + def _shape_info(self): + return [_ShapeInfo("kappa", False, (0, np.inf), (False, False))] + + def _pdf(self, x, kappa): + return np.exp(self._logpdf(x, kappa)) + + def _logpdf(self, x, kappa): + kapinv = 1/kappa + lPx = x * np.where(x >= 0, -kappa, kapinv) + lPx -= np.log(kappa+kapinv) + return lPx + + def _cdf(self, x, kappa): + kapinv = 1/kappa + kappkapinv = kappa+kapinv + return np.where(x >= 0, + 1 - np.exp(-x*kappa)*(kapinv/kappkapinv), + np.exp(x*kapinv)*(kappa/kappkapinv)) + + def _sf(self, x, kappa): + kapinv = 1/kappa + kappkapinv = kappa+kapinv + return np.where(x >= 0, + np.exp(-x*kappa)*(kapinv/kappkapinv), + 1 - np.exp(x*kapinv)*(kappa/kappkapinv)) + + def _ppf(self, q, kappa): + kapinv = 1/kappa + kappkapinv = kappa+kapinv + return np.where(q >= kappa/kappkapinv, + -np.log((1 - q)*kappkapinv*kappa)*kapinv, + np.log(q*kappkapinv/kappa)*kappa) + + def _isf(self, q, kappa): + kapinv = 1/kappa + kappkapinv = kappa+kapinv + return np.where(q <= kapinv/kappkapinv, + -np.log(q*kappkapinv*kappa)*kapinv, + np.log((1 - q)*kappkapinv/kappa)*kappa) + + def _stats(self, kappa): + kapinv = 1/kappa + mn = kapinv - kappa + var = kapinv*kapinv + kappa*kappa + g1 = 2.0*(1-np.power(kappa, 6))/np.power(1+np.power(kappa, 4), 1.5) + g2 = 6.0*(1+np.power(kappa, 8))/np.power(1+np.power(kappa, 4), 2) + return mn, var, g1, g2 + + def _entropy(self, kappa): + return 1 + np.log(kappa+1/kappa) + + +laplace_asymmetric = laplace_asymmetric_gen(name='laplace_asymmetric') + + +def _check_fit_input_parameters(dist, data, args, kwds): + if not isinstance(data, CensoredData): + data = np.asarray(data) + + floc = kwds.get('floc', None) + fscale = kwds.get('fscale', None) + + num_shapes = len(dist.shapes.split(",")) if dist.shapes else 0 + fshape_keys = [] + fshapes = [] + + # user has many options for fixing the shape, so here we standardize it + # into 'f' + the number of the shape. + # Adapted from `_reduce_func` in `_distn_infrastructure.py`: + if dist.shapes: + shapes = dist.shapes.replace(',', ' ').split() + for j, s in enumerate(shapes): + key = 'f' + str(j) + names = [key, 'f' + s, 'fix_' + s] + val = _get_fixed_fit_value(kwds, names) + fshape_keys.append(key) + fshapes.append(val) + if val is not None: + kwds[key] = val + + # determine if there are any unknown arguments in kwds + known_keys = {'loc', 'scale', 'optimizer', 'method', + 'floc', 'fscale', *fshape_keys} + unknown_keys = set(kwds).difference(known_keys) + if unknown_keys: + raise TypeError(f"Unknown keyword arguments: {unknown_keys}.") + + if len(args) > num_shapes: + raise TypeError("Too many positional arguments.") + + if None not in {floc, fscale, *fshapes}: + # This check is for consistency with `rv_continuous.fit`. + # Without this check, this function would just return the + # parameters that were given. + raise RuntimeError("All parameters fixed. There is nothing to " + "optimize.") + + uncensored = data._uncensor() if isinstance(data, CensoredData) else data + if not np.isfinite(uncensored).all(): + raise ValueError("The data contains non-finite values.") + + return (data, *fshapes, floc, fscale) + + +class levy_gen(rv_continuous): + r"""A Levy continuous random variable. + + %(before_notes)s + + See Also + -------- + levy_stable, levy_l + + Notes + ----- + The probability density function for `levy` is: + + .. math:: + + f(x) = \frac{1}{\sqrt{2\pi x^3}} \exp\left(-\frac{1}{2x}\right) + + for :math:`x > 0`. + + This is the same as the Levy-stable distribution with :math:`a=1/2` and + :math:`b=1`. + + %(after_notes)s + + Examples + -------- + >>> import numpy as np + >>> from scipy.stats import levy + >>> import matplotlib.pyplot as plt + >>> fig, ax = plt.subplots(1, 1) + + Calculate the first four moments: + + >>> mean, var, skew, kurt = levy.stats(moments='mvsk') + + Display the probability density function (``pdf``): + + >>> # `levy` is very heavy-tailed. + >>> # To show a nice plot, let's cut off the upper 40 percent. + >>> a, b = levy.ppf(0), levy.ppf(0.6) + >>> x = np.linspace(a, b, 100) + >>> ax.plot(x, levy.pdf(x), + ... 'r-', lw=5, alpha=0.6, label='levy pdf') + + Alternatively, the distribution object can be called (as a function) + to fix the shape, location and scale parameters. This returns a "frozen" + RV object holding the given parameters fixed. + + Freeze the distribution and display the frozen ``pdf``: + + >>> rv = levy() + >>> ax.plot(x, rv.pdf(x), 'k-', lw=2, label='frozen pdf') + + Check accuracy of ``cdf`` and ``ppf``: + + >>> vals = levy.ppf([0.001, 0.5, 0.999]) + >>> np.allclose([0.001, 0.5, 0.999], levy.cdf(vals)) + True + + Generate random numbers: + + >>> r = levy.rvs(size=1000) + + And compare the histogram: + + >>> # manual binning to ignore the tail + >>> bins = np.concatenate((np.linspace(a, b, 20), [np.max(r)])) + >>> ax.hist(r, bins=bins, density=True, histtype='stepfilled', alpha=0.2) + >>> ax.set_xlim([x[0], x[-1]]) + >>> ax.legend(loc='best', frameon=False) + >>> plt.show() + + """ + _support_mask = rv_continuous._open_support_mask + + def _shape_info(self): + return [] + + def _pdf(self, x): + # levy.pdf(x) = 1 / (x * sqrt(2*pi*x)) * exp(-1/(2*x)) + return 1 / np.sqrt(2*np.pi*x) / x * np.exp(-1/(2*x)) + + def _cdf(self, x): + # Equivalent to 2*norm.sf(np.sqrt(1/x)) + return sc.erfc(np.sqrt(0.5 / x)) + + def _sf(self, x): + return sc.erf(np.sqrt(0.5 / x)) + + def _ppf(self, q): + # Equivalent to 1.0/(norm.isf(q/2)**2) or 0.5/(erfcinv(q)**2) + val = _norm_isf(q/2) + return 1.0 / (val * val) + + def _isf(self, p): + return 1/(2*sc.erfinv(p)**2) + + def _stats(self): + return np.inf, np.inf, np.nan, np.nan + + +levy = levy_gen(a=0.0, name="levy") + + +class levy_l_gen(rv_continuous): + r"""A left-skewed Levy continuous random variable. + + %(before_notes)s + + See Also + -------- + levy, levy_stable + + Notes + ----- + The probability density function for `levy_l` is: + + .. math:: + f(x) = \frac{1}{|x| \sqrt{2\pi |x|}} \exp{ \left(-\frac{1}{2|x|} \right)} + + for :math:`x < 0`. + + This is the same as the Levy-stable distribution with :math:`a=1/2` and + :math:`b=-1`. + + %(after_notes)s + + Examples + -------- + >>> import numpy as np + >>> from scipy.stats import levy_l + >>> import matplotlib.pyplot as plt + >>> fig, ax = plt.subplots(1, 1) + + Calculate the first four moments: + + >>> mean, var, skew, kurt = levy_l.stats(moments='mvsk') + + Display the probability density function (``pdf``): + + >>> # `levy_l` is very heavy-tailed. + >>> # To show a nice plot, let's cut off the lower 40 percent. + >>> a, b = levy_l.ppf(0.4), levy_l.ppf(1) + >>> x = np.linspace(a, b, 100) + >>> ax.plot(x, levy_l.pdf(x), + ... 'r-', lw=5, alpha=0.6, label='levy_l pdf') + + Alternatively, the distribution object can be called (as a function) + to fix the shape, location and scale parameters. This returns a "frozen" + RV object holding the given parameters fixed. + + Freeze the distribution and display the frozen ``pdf``: + + >>> rv = levy_l() + >>> ax.plot(x, rv.pdf(x), 'k-', lw=2, label='frozen pdf') + + Check accuracy of ``cdf`` and ``ppf``: + + >>> vals = levy_l.ppf([0.001, 0.5, 0.999]) + >>> np.allclose([0.001, 0.5, 0.999], levy_l.cdf(vals)) + True + + Generate random numbers: + + >>> r = levy_l.rvs(size=1000) + + And compare the histogram: + + >>> # manual binning to ignore the tail + >>> bins = np.concatenate(([np.min(r)], np.linspace(a, b, 20))) + >>> ax.hist(r, bins=bins, density=True, histtype='stepfilled', alpha=0.2) + >>> ax.set_xlim([x[0], x[-1]]) + >>> ax.legend(loc='best', frameon=False) + >>> plt.show() + + """ + _support_mask = rv_continuous._open_support_mask + + def _shape_info(self): + return [] + + def _pdf(self, x): + # levy_l.pdf(x) = 1 / (abs(x) * sqrt(2*pi*abs(x))) * exp(-1/(2*abs(x))) + ax = abs(x) + return 1/np.sqrt(2*np.pi*ax)/ax*np.exp(-1/(2*ax)) + + def _cdf(self, x): + ax = abs(x) + return 2 * _norm_cdf(1 / np.sqrt(ax)) - 1 + + def _sf(self, x): + ax = abs(x) + return 2 * _norm_sf(1 / np.sqrt(ax)) + + def _ppf(self, q): + val = _norm_ppf((q + 1.0) / 2) + return -1.0 / (val * val) + + def _isf(self, p): + return -1/_norm_isf(p/2)**2 + + def _stats(self): + return np.inf, np.inf, np.nan, np.nan + + +levy_l = levy_l_gen(b=0.0, name="levy_l") + + +class logistic_gen(rv_continuous): + r"""A logistic (or Sech-squared) continuous random variable. + + %(before_notes)s + + Notes + ----- + The probability density function for `logistic` is: + + .. math:: + + f(x) = \frac{\exp(-x)} + {(1+\exp(-x))^2} + + `logistic` is a special case of `genlogistic` with ``c=1``. + + Remark that the survival function (``logistic.sf``) is equal to the + Fermi-Dirac distribution describing fermionic statistics. + + %(after_notes)s + + %(example)s + + """ + def _shape_info(self): + return [] + + def _rvs(self, size=None, random_state=None): + return random_state.logistic(size=size) + + def _pdf(self, x): + # logistic.pdf(x) = exp(-x) / (1+exp(-x))**2 + return np.exp(self._logpdf(x)) + + def _logpdf(self, x): + y = -np.abs(x) + return y - 2. * sc.log1p(np.exp(y)) + + def _cdf(self, x): + return sc.expit(x) + + def _logcdf(self, x): + return sc.log_expit(x) + + def _ppf(self, q): + return sc.logit(q) + + def _sf(self, x): + return sc.expit(-x) + + def _logsf(self, x): + return sc.log_expit(-x) + + def _isf(self, q): + return -sc.logit(q) + + def _stats(self): + return 0, np.pi*np.pi/3.0, 0, 6.0/5.0 + + def _entropy(self): + # https://en.wikipedia.org/wiki/Logistic_distribution + return 2.0 + + @_call_super_mom + @inherit_docstring_from(rv_continuous) + def fit(self, data, *args, **kwds): + if kwds.pop('superfit', False): + return super().fit(data, *args, **kwds) + + data, floc, fscale = _check_fit_input_parameters(self, data, + args, kwds) + n = len(data) + + # rv_continuous provided guesses + loc, scale = self._fitstart(data) + # these are trumped by user-provided guesses + loc, scale = kwds.get('loc', loc), kwds.get('scale', scale) + + # the maximum likelihood estimators `a` and `b` of the location and + # scale parameters are roots of the two equations described in `func`. + # Source: Statistical Distributions, 3rd Edition. Evans, Hastings, and + # Peacock (2000), Page 130 + + def dl_dloc(loc, scale=fscale): + c = (data - loc) / scale + return np.sum(sc.expit(c)) - n/2 + + def dl_dscale(scale, loc=floc): + c = (data - loc) / scale + return np.sum(c*np.tanh(c/2)) - n + + def func(params): + loc, scale = params + return dl_dloc(loc, scale), dl_dscale(scale, loc) + + if fscale is not None and floc is None: + res = optimize.root(dl_dloc, (loc,)) + loc = res.x[0] + scale = fscale + elif floc is not None and fscale is None: + res = optimize.root(dl_dscale, (scale,)) + scale = res.x[0] + loc = floc + else: + res = optimize.root(func, (loc, scale)) + loc, scale = res.x + + # Note: gh-18176 reported data for which the reported MLE had + # `scale < 0`. To fix the bug, we return abs(scale). This is OK because + # `dl_dscale` and `dl_dloc` are even and odd functions of `scale`, + # respectively, so if `-scale` is a solution, so is `scale`. + scale = abs(scale) + return ((loc, scale) if res.success + else super().fit(data, *args, **kwds)) + + +logistic = logistic_gen(name='logistic') + + +class loggamma_gen(rv_continuous): + r"""A log gamma continuous random variable. + + %(before_notes)s + + Notes + ----- + The probability density function for `loggamma` is: + + .. math:: + + f(x, c) = \frac{\exp(c x - \exp(x))} + {\Gamma(c)} + + for all :math:`x, c > 0`. Here, :math:`\Gamma` is the + gamma function (`scipy.special.gamma`). + + `loggamma` takes ``c`` as a shape parameter for :math:`c`. + + %(after_notes)s + + %(example)s + + """ + + def _shape_info(self): + return [_ShapeInfo("c", False, (0, np.inf), (False, False))] + + def _rvs(self, c, size=None, random_state=None): + # Use the property of the gamma distribution Gamma(c) + # Gamma(c) ~ Gamma(c + 1)*U**(1/c), + # where U is uniform on [0, 1]. (See, e.g., + # G. Marsaglia and W.W. Tsang, "A simple method for generating gamma + # variables", https://doi.org/10.1145/358407.358414) + # So + # log(Gamma(c)) ~ log(Gamma(c + 1)) + log(U)/c + # Generating a sample with this formulation is a bit slower + # than the more obvious log(Gamma(c)), but it avoids loss + # of precision when c << 1. + return (np.log(random_state.gamma(c + 1, size=size)) + + np.log(random_state.uniform(size=size))/c) + + def _pdf(self, x, c): + # loggamma.pdf(x, c) = exp(c*x-exp(x)) / gamma(c) + return np.exp(c*x-np.exp(x)-sc.gammaln(c)) + + def _logpdf(self, x, c): + return c*x - np.exp(x) - sc.gammaln(c) + + def _cdf(self, x, c): + # This function is gammainc(c, exp(x)), where gammainc(c, z) is + # the regularized incomplete gamma function. + # The first term in a series expansion of gamminc(c, z) is + # z**c/Gamma(c+1); see 6.5.29 of Abramowitz & Stegun (and refer + # back to 6.5.1, 6.5.2 and 6.5.4 for the relevant notation). + # This can also be found in the wikipedia article + # https://en.wikipedia.org/wiki/Incomplete_gamma_function. + # Here we use that formula when x is sufficiently negative that + # exp(x) will result in subnormal numbers and lose precision. + # We evaluate the log of the expression first to allow the possible + # cancellation of the terms in the division, and then exponentiate. + # That is, + # exp(x)**c/Gamma(c+1) = exp(log(exp(x)**c/Gamma(c+1))) + # = exp(c*x - gammaln(c+1)) + return _lazywhere(x < _LOGXMIN, (x, c), + lambda x, c: np.exp(c*x - sc.gammaln(c+1)), + f2=lambda x, c: sc.gammainc(c, np.exp(x))) + + def _ppf(self, q, c): + # The expression used when g < _XMIN inverts the one term expansion + # given in the comments of _cdf(). + g = sc.gammaincinv(c, q) + return _lazywhere(g < _XMIN, (g, q, c), + lambda g, q, c: (np.log(q) + sc.gammaln(c+1))/c, + f2=lambda g, q, c: np.log(g)) + + def _sf(self, x, c): + # See the comments for _cdf() for how x < _LOGXMIN is handled. + return _lazywhere(x < _LOGXMIN, (x, c), + lambda x, c: -np.expm1(c*x - sc.gammaln(c+1)), + f2=lambda x, c: sc.gammaincc(c, np.exp(x))) + + def _isf(self, q, c): + # The expression used when g < _XMIN inverts the complement of + # the one term expansion given in the comments of _cdf(). + g = sc.gammainccinv(c, q) + return _lazywhere(g < _XMIN, (g, q, c), + lambda g, q, c: (np.log1p(-q) + sc.gammaln(c+1))/c, + f2=lambda g, q, c: np.log(g)) + + def _stats(self, c): + # See, for example, "A Statistical Study of Log-Gamma Distribution", by + # Ping Shing Chan (thesis, McMaster University, 1993). + mean = sc.digamma(c) + var = sc.polygamma(1, c) + skewness = sc.polygamma(2, c) / np.power(var, 1.5) + excess_kurtosis = sc.polygamma(3, c) / (var*var) + return mean, var, skewness, excess_kurtosis + + def _entropy(self, c): + def regular(c): + h = sc.gammaln(c) - c * sc.digamma(c) + c + return h + + def asymptotic(c): + # using asymptotic expansions for gammaln and psi (see gh-18093) + term = -0.5*np.log(c) + c**-1./6 - c**-3./90 + c**-5./210 + h = norm._entropy() + term + return h + + h = _lazywhere(c >= 45, (c, ), f=asymptotic, f2=regular) + return h + + +loggamma = loggamma_gen(name='loggamma') + + +class loglaplace_gen(rv_continuous): + r"""A log-Laplace continuous random variable. + + %(before_notes)s + + Notes + ----- + The probability density function for `loglaplace` is: + + .. math:: + + f(x, c) = \begin{cases}\frac{c}{2} x^{ c-1} &\text{for } 0 < x < 1\\ + \frac{c}{2} x^{-c-1} &\text{for } x \ge 1 + \end{cases} + + for :math:`c > 0`. + + `loglaplace` takes ``c`` as a shape parameter for :math:`c`. + + %(after_notes)s + + Suppose a random variable ``X`` follows the Laplace distribution with + location ``a`` and scale ``b``. Then ``Y = exp(X)`` follows the + log-Laplace distribution with ``c = 1 / b`` and ``scale = exp(a)``. + + References + ---------- + T.J. Kozubowski and K. Podgorski, "A log-Laplace growth rate model", + The Mathematical Scientist, vol. 28, pp. 49-60, 2003. + + %(example)s + + """ + def _shape_info(self): + return [_ShapeInfo("c", False, (0, np.inf), (False, False))] + + def _pdf(self, x, c): + # loglaplace.pdf(x, c) = c / 2 * x**(c-1), for 0 < x < 1 + # = c / 2 * x**(-c-1), for x >= 1 + cd2 = c/2.0 + c = np.where(x < 1, c, -c) + return cd2*x**(c-1) + + def _cdf(self, x, c): + return np.where(x < 1, 0.5*x**c, 1-0.5*x**(-c)) + + def _sf(self, x, c): + return np.where(x < 1, 1 - 0.5*x**c, 0.5*x**(-c)) + + def _ppf(self, q, c): + return np.where(q < 0.5, (2.0*q)**(1.0/c), (2*(1.0-q))**(-1.0/c)) + + def _isf(self, q, c): + return np.where(q > 0.5, (2.0*(1.0 - q))**(1.0/c), (2*q)**(-1.0/c)) + + def _munp(self, n, c): + with np.errstate(divide='ignore'): + c2, n2 = c**2, n**2 + return np.where(n2 < c2, c2 / (c2 - n2), np.inf) + + def _entropy(self, c): + return np.log(2.0/c) + 1.0 + + @_call_super_mom + @inherit_docstring_from(rv_continuous) + def fit(self, data, *args, **kwds): + data, fc, floc, fscale = _check_fit_input_parameters(self, data, + args, kwds) + + # Specialize MLE only when location is known. + if floc is None: + return super(type(self), self).fit(data, *args, **kwds) + + # Raise an error if any observation has zero likelihood. + if np.any(data <= floc): + raise FitDataError("loglaplace", lower=floc, upper=np.inf) + + # Remove location from data. + if floc != 0: + data = data - floc + + # When location is zero, the log-Laplace distribution is related to + # the Laplace distribution in that if X ~ Laplace(loc=a, scale=b), + # then Y = exp(X) ~ LogLaplace(c=1/b, loc=0, scale=exp(a)). It can + # be shown that the MLE for Y is the same as the MLE for X = ln(Y). + # Therefore, we reuse the formulas from laplace.fit() and transform + # the result back into log-laplace's parameter space. + a, b = laplace.fit(np.log(data), + floc=np.log(fscale) if fscale is not None else None, + fscale=1/fc if fc is not None else None, + method='mle') + loc = floc + scale = np.exp(a) if fscale is None else fscale + c = 1 / b if fc is None else fc + return c, loc, scale + +loglaplace = loglaplace_gen(a=0.0, name='loglaplace') + + +def _lognorm_logpdf(x, s): + return _lazywhere(x != 0, (x, s), + lambda x, s: (-np.log(x)**2 / (2 * s**2) + - np.log(s * x * np.sqrt(2 * np.pi))), + -np.inf) + + +class lognorm_gen(rv_continuous): + r"""A lognormal continuous random variable. + + %(before_notes)s + + Notes + ----- + The probability density function for `lognorm` is: + + .. math:: + + f(x, s) = \frac{1}{s x \sqrt{2\pi}} + \exp\left(-\frac{\log^2(x)}{2s^2}\right) + + for :math:`x > 0`, :math:`s > 0`. + + `lognorm` takes ``s`` as a shape parameter for :math:`s`. + + %(after_notes)s + + Suppose a normally distributed random variable ``X`` has mean ``mu`` and + standard deviation ``sigma``. Then ``Y = exp(X)`` is lognormally + distributed with ``s = sigma`` and ``scale = exp(mu)``. + + %(example)s + + The logarithm of a log-normally distributed random variable is + normally distributed: + + >>> import numpy as np + >>> import matplotlib.pyplot as plt + >>> from scipy import stats + >>> fig, ax = plt.subplots(1, 1) + >>> mu, sigma = 2, 0.5 + >>> X = stats.norm(loc=mu, scale=sigma) + >>> Y = stats.lognorm(s=sigma, scale=np.exp(mu)) + >>> x = np.linspace(*X.interval(0.999)) + >>> y = Y.rvs(size=10000) + >>> ax.plot(x, X.pdf(x), label='X (pdf)') + >>> ax.hist(np.log(y), density=True, bins=x, label='log(Y) (histogram)') + >>> ax.legend() + >>> plt.show() + + """ + _support_mask = rv_continuous._open_support_mask + + def _shape_info(self): + return [_ShapeInfo("s", False, (0, np.inf), (False, False))] + + def _rvs(self, s, size=None, random_state=None): + return np.exp(s * random_state.standard_normal(size)) + + def _pdf(self, x, s): + # lognorm.pdf(x, s) = 1 / (s*x*sqrt(2*pi)) * exp(-1/2*(log(x)/s)**2) + return np.exp(self._logpdf(x, s)) + + def _logpdf(self, x, s): + return _lognorm_logpdf(x, s) + + def _cdf(self, x, s): + return _norm_cdf(np.log(x) / s) + + def _logcdf(self, x, s): + return _norm_logcdf(np.log(x) / s) + + def _ppf(self, q, s): + return np.exp(s * _norm_ppf(q)) + + def _sf(self, x, s): + return _norm_sf(np.log(x) / s) + + def _logsf(self, x, s): + return _norm_logsf(np.log(x) / s) + + def _isf(self, q, s): + return np.exp(s * _norm_isf(q)) + + def _stats(self, s): + p = np.exp(s*s) + mu = np.sqrt(p) + mu2 = p*(p-1) + g1 = np.sqrt(p-1)*(2+p) + g2 = np.polyval([1, 2, 3, 0, -6.0], p) + return mu, mu2, g1, g2 + + def _entropy(self, s): + return 0.5 * (1 + np.log(2*np.pi) + 2 * np.log(s)) + + @_call_super_mom + @extend_notes_in_docstring(rv_continuous, notes="""\ + When `method='MLE'` and + the location parameter is fixed by using the `floc` argument, + this function uses explicit formulas for the maximum likelihood + estimation of the log-normal shape and scale parameters, so the + `optimizer`, `loc` and `scale` keyword arguments are ignored. + If the location is free, a likelihood maximum is found by + setting its partial derivative wrt to location to 0, and + solving by substituting the analytical expressions of shape + and scale (or provided parameters). + See, e.g., equation 3.1 in + A. Clifford Cohen & Betty Jones Whitten (1980) + Estimation in the Three-Parameter Lognormal Distribution, + Journal of the American Statistical Association, 75:370, 399-404 + https://doi.org/10.2307/2287466 + \n\n""") + def fit(self, data, *args, **kwds): + if kwds.pop('superfit', False): + return super().fit(data, *args, **kwds) + + parameters = _check_fit_input_parameters(self, data, args, kwds) + data, fshape, floc, fscale = parameters + data_min = np.min(data) + + def get_shape_scale(loc): + # Calculate maximum likelihood scale and shape with analytical + # formulas unless provided by the user + if fshape is None or fscale is None: + lndata = np.log(data - loc) + scale = fscale or np.exp(lndata.mean()) + shape = fshape or np.sqrt(np.mean((lndata - np.log(scale))**2)) + return shape, scale + + def dL_dLoc(loc): + # Derivative of (positive) LL w.r.t. loc + shape, scale = get_shape_scale(loc) + shifted = data - loc + return np.sum((1 + np.log(shifted/scale)/shape**2)/shifted) + + def ll(loc): + # (Positive) log-likelihood + shape, scale = get_shape_scale(loc) + return -self.nnlf((shape, loc, scale), data) + + if floc is None: + # The location must be less than the minimum of the data. + # Back off a bit to avoid numerical issues. + spacing = np.spacing(data_min) + rbrack = data_min - spacing + + # Find the right end of the bracket by successive doubling of the + # distance to data_min. We're interested in a maximum LL, so the + # slope dL_dLoc_rbrack should be negative at the right end. + # optimization for later: share shape, scale + dL_dLoc_rbrack = dL_dLoc(rbrack) + ll_rbrack = ll(rbrack) + delta = 2 * spacing # 2 * (data_min - rbrack) + while dL_dLoc_rbrack >= -1e-6: + rbrack = data_min - delta + dL_dLoc_rbrack = dL_dLoc(rbrack) + delta *= 2 + + if not np.isfinite(rbrack) or not np.isfinite(dL_dLoc_rbrack): + # If we never find a negative slope, either we missed it or the + # slope is always positive. It's usually the latter, + # which means + # loc = data_min - spacing + # But sometimes when shape and/or scale are fixed there are + # other issues, so be cautious. + return super().fit(data, *args, **kwds) + + # Now find the left end of the bracket. Guess is `rbrack-1` + # unless that is too small of a difference to resolve. Double + # the size of the interval until the left end is found. + lbrack = np.minimum(np.nextafter(rbrack, -np.inf), rbrack-1) + dL_dLoc_lbrack = dL_dLoc(lbrack) + delta = 2 * (rbrack - lbrack) + while (np.isfinite(lbrack) and np.isfinite(dL_dLoc_lbrack) + and np.sign(dL_dLoc_lbrack) == np.sign(dL_dLoc_rbrack)): + lbrack = rbrack - delta + dL_dLoc_lbrack = dL_dLoc(lbrack) + delta *= 2 + + # I don't recall observing this, but just in case... + if not np.isfinite(lbrack) or not np.isfinite(dL_dLoc_lbrack): + return super().fit(data, *args, **kwds) + + # If we have a valid bracket, find the root + res = root_scalar(dL_dLoc, bracket=(lbrack, rbrack)) + if not res.converged: + return super().fit(data, *args, **kwds) + + # If the slope was positive near the minimum of the data, + # the maximum LL could be there instead of at the root. Compare + # the LL of the two points to decide. + ll_root = ll(res.root) + loc = res.root if ll_root > ll_rbrack else data_min-spacing + + else: + if floc >= data_min: + raise FitDataError("lognorm", lower=0., upper=np.inf) + loc = floc + + shape, scale = get_shape_scale(loc) + if not (self._argcheck(shape) and scale > 0): + return super().fit(data, *args, **kwds) + return shape, loc, scale + + +lognorm = lognorm_gen(a=0.0, name='lognorm') + + +class gibrat_gen(rv_continuous): + r"""A Gibrat continuous random variable. + + %(before_notes)s + + Notes + ----- + The probability density function for `gibrat` is: + + .. math:: + + f(x) = \frac{1}{x \sqrt{2\pi}} \exp(-\frac{1}{2} (\log(x))^2) + + `gibrat` is a special case of `lognorm` with ``s=1``. + + %(after_notes)s + + %(example)s + + """ + _support_mask = rv_continuous._open_support_mask + + def _shape_info(self): + return [] + + def _rvs(self, size=None, random_state=None): + return np.exp(random_state.standard_normal(size)) + + def _pdf(self, x): + # gibrat.pdf(x) = 1/(x*sqrt(2*pi)) * exp(-1/2*(log(x))**2) + return np.exp(self._logpdf(x)) + + def _logpdf(self, x): + return _lognorm_logpdf(x, 1.0) + + def _cdf(self, x): + return _norm_cdf(np.log(x)) + + def _ppf(self, q): + return np.exp(_norm_ppf(q)) + + def _sf(self, x): + return _norm_sf(np.log(x)) + + def _isf(self, p): + return np.exp(_norm_isf(p)) + + def _stats(self): + p = np.e + mu = np.sqrt(p) + mu2 = p * (p - 1) + g1 = np.sqrt(p - 1) * (2 + p) + g2 = np.polyval([1, 2, 3, 0, -6.0], p) + return mu, mu2, g1, g2 + + def _entropy(self): + return 0.5 * np.log(2 * np.pi) + 0.5 + + +gibrat = gibrat_gen(a=0.0, name='gibrat') + + +class maxwell_gen(rv_continuous): + r"""A Maxwell continuous random variable. + + %(before_notes)s + + Notes + ----- + A special case of a `chi` distribution, with ``df=3``, ``loc=0.0``, + and given ``scale = a``, where ``a`` is the parameter used in the + Mathworld description [1]_. + + The probability density function for `maxwell` is: + + .. math:: + + f(x) = \sqrt{2/\pi}x^2 \exp(-x^2/2) + + for :math:`x >= 0`. + + %(after_notes)s + + References + ---------- + .. [1] http://mathworld.wolfram.com/MaxwellDistribution.html + + %(example)s + """ + def _shape_info(self): + return [] + + def _rvs(self, size=None, random_state=None): + return chi.rvs(3.0, size=size, random_state=random_state) + + def _pdf(self, x): + # maxwell.pdf(x) = sqrt(2/pi)x**2 * exp(-x**2/2) + return _SQRT_2_OVER_PI*x*x*np.exp(-x*x/2.0) + + def _logpdf(self, x): + # Allow x=0 without 'divide by zero' warnings + with np.errstate(divide='ignore'): + return _LOG_SQRT_2_OVER_PI + 2*np.log(x) - 0.5*x*x + + def _cdf(self, x): + return sc.gammainc(1.5, x*x/2.0) + + def _ppf(self, q): + return np.sqrt(2*sc.gammaincinv(1.5, q)) + + def _sf(self, x): + return sc.gammaincc(1.5, x*x/2.0) + + def _isf(self, q): + return np.sqrt(2*sc.gammainccinv(1.5, q)) + + def _stats(self): + val = 3*np.pi-8 + return (2*np.sqrt(2.0/np.pi), + 3-8/np.pi, + np.sqrt(2)*(32-10*np.pi)/val**1.5, + (-12*np.pi*np.pi + 160*np.pi - 384) / val**2.0) + + def _entropy(self): + return _EULER + 0.5*np.log(2*np.pi)-0.5 + + +maxwell = maxwell_gen(a=0.0, name='maxwell') + + +class mielke_gen(rv_continuous): + r"""A Mielke Beta-Kappa / Dagum continuous random variable. + + %(before_notes)s + + Notes + ----- + The probability density function for `mielke` is: + + .. math:: + + f(x, k, s) = \frac{k x^{k-1}}{(1+x^s)^{1+k/s}} + + for :math:`x > 0` and :math:`k, s > 0`. The distribution is sometimes + called Dagum distribution ([2]_). It was already defined in [3]_, called + a Burr Type III distribution (`burr` with parameters ``c=s`` and + ``d=k/s``). + + `mielke` takes ``k`` and ``s`` as shape parameters. + + %(after_notes)s + + References + ---------- + .. [1] Mielke, P.W., 1973 "Another Family of Distributions for Describing + and Analyzing Precipitation Data." J. Appl. Meteor., 12, 275-280 + .. [2] Dagum, C., 1977 "A new model for personal income distribution." + Economie Appliquee, 33, 327-367. + .. [3] Burr, I. W. "Cumulative frequency functions", Annals of + Mathematical Statistics, 13(2), pp 215-232 (1942). + + %(example)s + + """ + def _shape_info(self): + ik = _ShapeInfo("k", False, (0, np.inf), (False, False)) + i_s = _ShapeInfo("s", False, (0, np.inf), (False, False)) + return [ik, i_s] + + def _pdf(self, x, k, s): + return k*x**(k-1.0) / (1.0+x**s)**(1.0+k*1.0/s) + + def _logpdf(self, x, k, s): + # Allow x=0 without 'divide by zero' warnings. + with np.errstate(divide='ignore'): + return np.log(k) + np.log(x)*(k - 1) - np.log1p(x**s)*(1 + k/s) + + def _cdf(self, x, k, s): + return x**k / (1.0+x**s)**(k*1.0/s) + + def _ppf(self, q, k, s): + qsk = pow(q, s*1.0/k) + return pow(qsk/(1.0-qsk), 1.0/s) + + def _munp(self, n, k, s): + def nth_moment(n, k, s): + # n-th moment is defined for -k < n < s + return sc.gamma((k+n)/s)*sc.gamma(1-n/s)/sc.gamma(k/s) + + return _lazywhere(n < s, (n, k, s), nth_moment, np.inf) + + +mielke = mielke_gen(a=0.0, name='mielke') + + +class kappa4_gen(rv_continuous): + r"""Kappa 4 parameter distribution. + + %(before_notes)s + + Notes + ----- + The probability density function for kappa4 is: + + .. math:: + + f(x, h, k) = (1 - k x)^{1/k - 1} (1 - h (1 - k x)^{1/k})^{1/h-1} + + if :math:`h` and :math:`k` are not equal to 0. + + If :math:`h` or :math:`k` are zero then the pdf can be simplified: + + h = 0 and k != 0:: + + kappa4.pdf(x, h, k) = (1.0 - k*x)**(1.0/k - 1.0)* + exp(-(1.0 - k*x)**(1.0/k)) + + h != 0 and k = 0:: + + kappa4.pdf(x, h, k) = exp(-x)*(1.0 - h*exp(-x))**(1.0/h - 1.0) + + h = 0 and k = 0:: + + kappa4.pdf(x, h, k) = exp(-x)*exp(-exp(-x)) + + kappa4 takes :math:`h` and :math:`k` as shape parameters. + + The kappa4 distribution returns other distributions when certain + :math:`h` and :math:`k` values are used. + + +------+-------------+----------------+------------------+ + | h | k=0.0 | k=1.0 | -inf<=k<=inf | + +======+=============+================+==================+ + | -1.0 | Logistic | | Generalized | + | | | | Logistic(1) | + | | | | | + | | logistic(x) | | | + +------+-------------+----------------+------------------+ + | 0.0 | Gumbel | Reverse | Generalized | + | | | Exponential(2) | Extreme Value | + | | | | | + | | gumbel_r(x) | | genextreme(x, k) | + +------+-------------+----------------+------------------+ + | 1.0 | Exponential | Uniform | Generalized | + | | | | Pareto | + | | | | | + | | expon(x) | uniform(x) | genpareto(x, -k) | + +------+-------------+----------------+------------------+ + + (1) There are at least five generalized logistic distributions. + Four are described here: + https://en.wikipedia.org/wiki/Generalized_logistic_distribution + The "fifth" one is the one kappa4 should match which currently + isn't implemented in scipy: + https://en.wikipedia.org/wiki/Talk:Generalized_logistic_distribution + https://www.mathwave.com/help/easyfit/html/analyses/distributions/gen_logistic.html + (2) This distribution is currently not in scipy. + + References + ---------- + J.C. Finney, "Optimization of a Skewed Logistic Distribution With Respect + to the Kolmogorov-Smirnov Test", A Dissertation Submitted to the Graduate + Faculty of the Louisiana State University and Agricultural and Mechanical + College, (August, 2004), + https://digitalcommons.lsu.edu/gradschool_dissertations/3672 + + J.R.M. Hosking, "The four-parameter kappa distribution". IBM J. Res. + Develop. 38 (3), 25 1-258 (1994). + + B. Kumphon, A. Kaew-Man, P. Seenoi, "A Rainfall Distribution for the Lampao + Site in the Chi River Basin, Thailand", Journal of Water Resource and + Protection, vol. 4, 866-869, (2012). + :doi:`10.4236/jwarp.2012.410101` + + C. Winchester, "On Estimation of the Four-Parameter Kappa Distribution", A + Thesis Submitted to Dalhousie University, Halifax, Nova Scotia, (March + 2000). + http://www.nlc-bnc.ca/obj/s4/f2/dsk2/ftp01/MQ57336.pdf + + %(after_notes)s + + %(example)s + + """ + def _argcheck(self, h, k): + shape = np.broadcast_arrays(h, k)[0].shape + return np.full(shape, fill_value=True) + + def _shape_info(self): + ih = _ShapeInfo("h", False, (-np.inf, np.inf), (False, False)) + ik = _ShapeInfo("k", False, (-np.inf, np.inf), (False, False)) + return [ih, ik] + + def _get_support(self, h, k): + condlist = [np.logical_and(h > 0, k > 0), + np.logical_and(h > 0, k == 0), + np.logical_and(h > 0, k < 0), + np.logical_and(h <= 0, k > 0), + np.logical_and(h <= 0, k == 0), + np.logical_and(h <= 0, k < 0)] + + def f0(h, k): + return (1.0 - np.float_power(h, -k))/k + + def f1(h, k): + return np.log(h) + + def f3(h, k): + a = np.empty(np.shape(h)) + a[:] = -np.inf + return a + + def f5(h, k): + return 1.0/k + + _a = _lazyselect(condlist, + [f0, f1, f0, f3, f3, f5], + [h, k], + default=np.nan) + + def f0(h, k): + return 1.0/k + + def f1(h, k): + a = np.empty(np.shape(h)) + a[:] = np.inf + return a + + _b = _lazyselect(condlist, + [f0, f1, f1, f0, f1, f1], + [h, k], + default=np.nan) + return _a, _b + + def _pdf(self, x, h, k): + # kappa4.pdf(x, h, k) = (1.0 - k*x)**(1.0/k - 1.0)* + # (1.0 - h*(1.0 - k*x)**(1.0/k))**(1.0/h-1) + return np.exp(self._logpdf(x, h, k)) + + def _logpdf(self, x, h, k): + condlist = [np.logical_and(h != 0, k != 0), + np.logical_and(h == 0, k != 0), + np.logical_and(h != 0, k == 0), + np.logical_and(h == 0, k == 0)] + + def f0(x, h, k): + '''pdf = (1.0 - k*x)**(1.0/k - 1.0)*( + 1.0 - h*(1.0 - k*x)**(1.0/k))**(1.0/h-1.0) + logpdf = ... + ''' + return (sc.xlog1py(1.0/k - 1.0, -k*x) + + sc.xlog1py(1.0/h - 1.0, -h*(1.0 - k*x)**(1.0/k))) + + def f1(x, h, k): + '''pdf = (1.0 - k*x)**(1.0/k - 1.0)*np.exp(-( + 1.0 - k*x)**(1.0/k)) + logpdf = ... + ''' + return sc.xlog1py(1.0/k - 1.0, -k*x) - (1.0 - k*x)**(1.0/k) + + def f2(x, h, k): + '''pdf = np.exp(-x)*(1.0 - h*np.exp(-x))**(1.0/h - 1.0) + logpdf = ... + ''' + return -x + sc.xlog1py(1.0/h - 1.0, -h*np.exp(-x)) + + def f3(x, h, k): + '''pdf = np.exp(-x-np.exp(-x)) + logpdf = ... + ''' + return -x - np.exp(-x) + + return _lazyselect(condlist, + [f0, f1, f2, f3], + [x, h, k], + default=np.nan) + + def _cdf(self, x, h, k): + return np.exp(self._logcdf(x, h, k)) + + def _logcdf(self, x, h, k): + condlist = [np.logical_and(h != 0, k != 0), + np.logical_and(h == 0, k != 0), + np.logical_and(h != 0, k == 0), + np.logical_and(h == 0, k == 0)] + + def f0(x, h, k): + '''cdf = (1.0 - h*(1.0 - k*x)**(1.0/k))**(1.0/h) + logcdf = ... + ''' + return (1.0/h)*sc.log1p(-h*(1.0 - k*x)**(1.0/k)) + + def f1(x, h, k): + '''cdf = np.exp(-(1.0 - k*x)**(1.0/k)) + logcdf = ... + ''' + return -(1.0 - k*x)**(1.0/k) + + def f2(x, h, k): + '''cdf = (1.0 - h*np.exp(-x))**(1.0/h) + logcdf = ... + ''' + return (1.0/h)*sc.log1p(-h*np.exp(-x)) + + def f3(x, h, k): + '''cdf = np.exp(-np.exp(-x)) + logcdf = ... + ''' + return -np.exp(-x) + + return _lazyselect(condlist, + [f0, f1, f2, f3], + [x, h, k], + default=np.nan) + + def _ppf(self, q, h, k): + condlist = [np.logical_and(h != 0, k != 0), + np.logical_and(h == 0, k != 0), + np.logical_and(h != 0, k == 0), + np.logical_and(h == 0, k == 0)] + + def f0(q, h, k): + return 1.0/k*(1.0 - ((1.0 - (q**h))/h)**k) + + def f1(q, h, k): + return 1.0/k*(1.0 - (-np.log(q))**k) + + def f2(q, h, k): + '''ppf = -np.log((1.0 - (q**h))/h) + ''' + return -sc.log1p(-(q**h)) + np.log(h) + + def f3(q, h, k): + return -np.log(-np.log(q)) + + return _lazyselect(condlist, + [f0, f1, f2, f3], + [q, h, k], + default=np.nan) + + def _get_stats_info(self, h, k): + condlist = [ + np.logical_and(h < 0, k >= 0), + k < 0, + ] + + def f0(h, k): + return (-1.0/h*k).astype(int) + + def f1(h, k): + return (-1.0/k).astype(int) + + return _lazyselect(condlist, [f0, f1], [h, k], default=5) + + def _stats(self, h, k): + maxr = self._get_stats_info(h, k) + outputs = [None if np.any(r < maxr) else np.nan for r in range(1, 5)] + return outputs[:] + + def _mom1_sc(self, m, *args): + maxr = self._get_stats_info(args[0], args[1]) + if m >= maxr: + return np.nan + return integrate.quad(self._mom_integ1, 0, 1, args=(m,)+args)[0] + + +kappa4 = kappa4_gen(name='kappa4') + + +class kappa3_gen(rv_continuous): + r"""Kappa 3 parameter distribution. + + %(before_notes)s + + Notes + ----- + The probability density function for `kappa3` is: + + .. math:: + + f(x, a) = a (a + x^a)^{-(a + 1)/a} + + for :math:`x > 0` and :math:`a > 0`. + + `kappa3` takes ``a`` as a shape parameter for :math:`a`. + + References + ---------- + P.W. Mielke and E.S. Johnson, "Three-Parameter Kappa Distribution Maximum + Likelihood and Likelihood Ratio Tests", Methods in Weather Research, + 701-707, (September, 1973), + :doi:`10.1175/1520-0493(1973)101<0701:TKDMLE>2.3.CO;2` + + B. Kumphon, "Maximum Entropy and Maximum Likelihood Estimation for the + Three-Parameter Kappa Distribution", Open Journal of Statistics, vol 2, + 415-419 (2012), :doi:`10.4236/ojs.2012.24050` + + %(after_notes)s + + %(example)s + + """ + def _shape_info(self): + return [_ShapeInfo("a", False, (0, np.inf), (False, False))] + + def _pdf(self, x, a): + # kappa3.pdf(x, a) = a*(a + x**a)**(-(a + 1)/a), for x > 0 + return a*(a + x**a)**(-1.0/a-1) + + def _cdf(self, x, a): + return x*(a + x**a)**(-1.0/a) + + def _sf(self, x, a): + x, a = np.broadcast_arrays(x, a) # some code paths pass scalars + sf = super()._sf(x, a) + + # When the SF is small, another formulation is typically more accurate. + # However, it blows up for large `a`, so use it only if it also returns + # a small value of the SF. + cutoff = 0.01 + i = sf < cutoff + sf2 = -sc.expm1(sc.xlog1py(-1.0 / a[i], a[i] * x[i]**-a[i])) + i2 = sf2 > cutoff + sf2[i2] = sf[i][i2] # replace bad values with original values + + sf[i] = sf2 + return sf + + def _ppf(self, q, a): + return (a/(q**-a - 1.0))**(1.0/a) + + def _isf(self, q, a): + lg = sc.xlog1py(-a, -q) + denom = sc.expm1(lg) + return (a / denom)**(1.0 / a) + + def _stats(self, a): + outputs = [None if np.any(i < a) else np.nan for i in range(1, 5)] + return outputs[:] + + def _mom1_sc(self, m, *args): + if np.any(m >= args[0]): + return np.nan + return integrate.quad(self._mom_integ1, 0, 1, args=(m,)+args)[0] + + +kappa3 = kappa3_gen(a=0.0, name='kappa3') + + +class moyal_gen(rv_continuous): + r"""A Moyal continuous random variable. + + %(before_notes)s + + Notes + ----- + The probability density function for `moyal` is: + + .. math:: + + f(x) = \exp(-(x + \exp(-x))/2) / \sqrt{2\pi} + + for a real number :math:`x`. + + %(after_notes)s + + This distribution has utility in high-energy physics and radiation + detection. It describes the energy loss of a charged relativistic + particle due to ionization of the medium [1]_. It also provides an + approximation for the Landau distribution. For an in depth description + see [2]_. For additional description, see [3]_. + + References + ---------- + .. [1] J.E. Moyal, "XXX. Theory of ionization fluctuations", + The London, Edinburgh, and Dublin Philosophical Magazine + and Journal of Science, vol 46, 263-280, (1955). + :doi:`10.1080/14786440308521076` (gated) + .. [2] G. Cordeiro et al., "The beta Moyal: a useful skew distribution", + International Journal of Research and Reviews in Applied Sciences, + vol 10, 171-192, (2012). + http://www.arpapress.com/Volumes/Vol10Issue2/IJRRAS_10_2_02.pdf + .. [3] C. Walck, "Handbook on Statistical Distributions for + Experimentalists; International Report SUF-PFY/96-01", Chapter 26, + University of Stockholm: Stockholm, Sweden, (2007). + http://www.stat.rice.edu/~dobelman/textfiles/DistributionsHandbook.pdf + + .. versionadded:: 1.1.0 + + %(example)s + + """ + def _shape_info(self): + return [] + + def _rvs(self, size=None, random_state=None): + u1 = gamma.rvs(a=0.5, scale=2, size=size, + random_state=random_state) + return -np.log(u1) + + def _pdf(self, x): + return np.exp(-0.5 * (x + np.exp(-x))) / np.sqrt(2*np.pi) + + def _cdf(self, x): + return sc.erfc(np.exp(-0.5 * x) / np.sqrt(2)) + + def _sf(self, x): + return sc.erf(np.exp(-0.5 * x) / np.sqrt(2)) + + def _ppf(self, x): + return -np.log(2 * sc.erfcinv(x)**2) + + def _stats(self): + mu = np.log(2) + np.euler_gamma + mu2 = np.pi**2 / 2 + g1 = 28 * np.sqrt(2) * sc.zeta(3) / np.pi**3 + g2 = 4. + return mu, mu2, g1, g2 + + def _munp(self, n): + if n == 1.0: + return np.log(2) + np.euler_gamma + elif n == 2.0: + return np.pi**2 / 2 + (np.log(2) + np.euler_gamma)**2 + elif n == 3.0: + tmp1 = 1.5 * np.pi**2 * (np.log(2)+np.euler_gamma) + tmp2 = (np.log(2)+np.euler_gamma)**3 + tmp3 = 14 * sc.zeta(3) + return tmp1 + tmp2 + tmp3 + elif n == 4.0: + tmp1 = 4 * 14 * sc.zeta(3) * (np.log(2) + np.euler_gamma) + tmp2 = 3 * np.pi**2 * (np.log(2) + np.euler_gamma)**2 + tmp3 = (np.log(2) + np.euler_gamma)**4 + tmp4 = 7 * np.pi**4 / 4 + return tmp1 + tmp2 + tmp3 + tmp4 + else: + # return generic for higher moments + # return rv_continuous._mom1_sc(self, n, b) + return self._mom1_sc(n) + + +moyal = moyal_gen(name="moyal") + + +class nakagami_gen(rv_continuous): + r"""A Nakagami continuous random variable. + + %(before_notes)s + + Notes + ----- + The probability density function for `nakagami` is: + + .. math:: + + f(x, \nu) = \frac{2 \nu^\nu}{\Gamma(\nu)} x^{2\nu-1} \exp(-\nu x^2) + + for :math:`x >= 0`, :math:`\nu > 0`. The distribution was introduced in + [2]_, see also [1]_ for further information. + + `nakagami` takes ``nu`` as a shape parameter for :math:`\nu`. + + %(after_notes)s + + References + ---------- + .. [1] "Nakagami distribution", Wikipedia + https://en.wikipedia.org/wiki/Nakagami_distribution + .. [2] M. Nakagami, "The m-distribution - A general formula of intensity + distribution of rapid fading", Statistical methods in radio wave + propagation, Pergamon Press, 1960, 3-36. + :doi:`10.1016/B978-0-08-009306-2.50005-4` + + %(example)s + + """ + def _argcheck(self, nu): + return nu > 0 + + def _shape_info(self): + return [_ShapeInfo("nu", False, (0, np.inf), (False, False))] + + def _pdf(self, x, nu): + return np.exp(self._logpdf(x, nu)) + + def _logpdf(self, x, nu): + # nakagami.pdf(x, nu) = 2 * nu**nu / gamma(nu) * + # x**(2*nu-1) * exp(-nu*x**2) + return (np.log(2) + sc.xlogy(nu, nu) - sc.gammaln(nu) + + sc.xlogy(2*nu - 1, x) - nu*x**2) + + def _cdf(self, x, nu): + return sc.gammainc(nu, nu*x*x) + + def _ppf(self, q, nu): + return np.sqrt(1.0/nu*sc.gammaincinv(nu, q)) + + def _sf(self, x, nu): + return sc.gammaincc(nu, nu*x*x) + + def _isf(self, p, nu): + return np.sqrt(1/nu * sc.gammainccinv(nu, p)) + + def _stats(self, nu): + mu = sc.poch(nu, 0.5)/np.sqrt(nu) + mu2 = 1.0-mu*mu + g1 = mu * (1 - 4*nu*mu2) / 2.0 / nu / np.power(mu2, 1.5) + g2 = -6*mu**4*nu + (8*nu-2)*mu**2-2*nu + 1 + g2 /= nu*mu2**2.0 + return mu, mu2, g1, g2 + + def _entropy(self, nu): + shape = np.shape(nu) + # because somehow this isn't taken care of by the infrastructure... + nu = np.atleast_1d(nu) + A = sc.gammaln(nu) + B = nu - (nu - 0.5) * sc.digamma(nu) + C = -0.5 * np.log(nu) - np.log(2) + h = A + B + C + # This is the asymptotic sum of A and B (see gh-17868) + norm_entropy = stats.norm._entropy() + # Above, this is lost to rounding error for large nu, so use the + # asymptotic sum when the approximation becomes accurate + i = nu > 5e4 # roundoff error ~ approximation error + # -1 / (12 * nu) is the O(1/nu) term; see gh-17929 + h[i] = C[i] + norm_entropy - 1/(12*nu[i]) + return h.reshape(shape)[()] + + def _rvs(self, nu, size=None, random_state=None): + # this relationship can be found in [1] or by a direct calculation + return np.sqrt(random_state.standard_gamma(nu, size=size) / nu) + + def _fitstart(self, data, args=None): + if isinstance(data, CensoredData): + data = data._uncensor() + if args is None: + args = (1.0,) * self.numargs + # Analytical justified estimates + # see: https://docs.scipy.org/doc/scipy/reference/tutorial/stats/continuous_nakagami.html + loc = np.min(data) + scale = np.sqrt(np.sum((data - loc)**2) / len(data)) + return args + (loc, scale) + + +nakagami = nakagami_gen(a=0.0, name="nakagami") + + +# The function name ncx2 is an abbreviation for noncentral chi squared. +def _ncx2_log_pdf(x, df, nc): + # We use (xs**2 + ns**2)/2 = (xs - ns)**2/2 + xs*ns, and include the + # factor of exp(-xs*ns) into the ive function to improve numerical + # stability at large values of xs. See also `rice.pdf`. + df2 = df/2.0 - 1.0 + xs, ns = np.sqrt(x), np.sqrt(nc) + res = sc.xlogy(df2/2.0, x/nc) - 0.5*(xs - ns)**2 + corr = sc.ive(df2, xs*ns) / 2.0 + # Return res + np.log(corr) avoiding np.log(0) + return _lazywhere( + corr > 0, + (res, corr), + f=lambda r, c: r + np.log(c), + fillvalue=-np.inf) + + +class ncx2_gen(rv_continuous): + r"""A non-central chi-squared continuous random variable. + + %(before_notes)s + + Notes + ----- + The probability density function for `ncx2` is: + + .. math:: + + f(x, k, \lambda) = \frac{1}{2} \exp(-(\lambda+x)/2) + (x/\lambda)^{(k-2)/4} I_{(k-2)/2}(\sqrt{\lambda x}) + + for :math:`x >= 0`, :math:`k > 0` and :math:`\lambda \ge 0`. + :math:`k` specifies the degrees of freedom (denoted ``df`` in the + implementation) and :math:`\lambda` is the non-centrality parameter + (denoted ``nc`` in the implementation). :math:`I_\nu` denotes the + modified Bessel function of first order of degree :math:`\nu` + (`scipy.special.iv`). + + `ncx2` takes ``df`` and ``nc`` as shape parameters. + + %(after_notes)s + + %(example)s + + """ + def _argcheck(self, df, nc): + return (df > 0) & np.isfinite(df) & (nc >= 0) + + def _shape_info(self): + idf = _ShapeInfo("df", False, (0, np.inf), (False, False)) + inc = _ShapeInfo("nc", False, (0, np.inf), (True, False)) + return [idf, inc] + + def _rvs(self, df, nc, size=None, random_state=None): + return random_state.noncentral_chisquare(df, nc, size) + + def _logpdf(self, x, df, nc): + cond = np.ones_like(x, dtype=bool) & (nc != 0) + return _lazywhere(cond, (x, df, nc), f=_ncx2_log_pdf, + f2=lambda x, df, _: chi2._logpdf(x, df)) + + def _pdf(self, x, df, nc): + cond = np.ones_like(x, dtype=bool) & (nc != 0) + with np.errstate(over='ignore'): # see gh-17432 + return _lazywhere(cond, (x, df, nc), f=_boost._ncx2_pdf, + f2=lambda x, df, _: chi2._pdf(x, df)) + + def _cdf(self, x, df, nc): + cond = np.ones_like(x, dtype=bool) & (nc != 0) + with np.errstate(over='ignore'): # see gh-17432 + return _lazywhere(cond, (x, df, nc), f=_boost._ncx2_cdf, + f2=lambda x, df, _: chi2._cdf(x, df)) + + def _ppf(self, q, df, nc): + cond = np.ones_like(q, dtype=bool) & (nc != 0) + with np.errstate(over='ignore'): # see gh-17432 + return _lazywhere(cond, (q, df, nc), f=_boost._ncx2_ppf, + f2=lambda x, df, _: chi2._ppf(x, df)) + + def _sf(self, x, df, nc): + cond = np.ones_like(x, dtype=bool) & (nc != 0) + with np.errstate(over='ignore'): # see gh-17432 + return _lazywhere(cond, (x, df, nc), f=_boost._ncx2_sf, + f2=lambda x, df, _: chi2._sf(x, df)) + + def _isf(self, x, df, nc): + cond = np.ones_like(x, dtype=bool) & (nc != 0) + with np.errstate(over='ignore'): # see gh-17432 + return _lazywhere(cond, (x, df, nc), f=_boost._ncx2_isf, + f2=lambda x, df, _: chi2._isf(x, df)) + + def _stats(self, df, nc): + return ( + _boost._ncx2_mean(df, nc), + _boost._ncx2_variance(df, nc), + _boost._ncx2_skewness(df, nc), + _boost._ncx2_kurtosis_excess(df, nc), + ) + + +ncx2 = ncx2_gen(a=0.0, name='ncx2') + + +class ncf_gen(rv_continuous): + r"""A non-central F distribution continuous random variable. + + %(before_notes)s + + See Also + -------- + scipy.stats.f : Fisher distribution + + Notes + ----- + The probability density function for `ncf` is: + + .. math:: + + f(x, n_1, n_2, \lambda) = + \exp\left(\frac{\lambda}{2} + + \lambda n_1 \frac{x}{2(n_1 x + n_2)} + \right) + n_1^{n_1/2} n_2^{n_2/2} x^{n_1/2 - 1} \\ + (n_2 + n_1 x)^{-(n_1 + n_2)/2} + \gamma(n_1/2) \gamma(1 + n_2/2) \\ + \frac{L^{\frac{n_1}{2}-1}_{n_2/2} + \left(-\lambda n_1 \frac{x}{2(n_1 x + n_2)}\right)} + {B(n_1/2, n_2/2) + \gamma\left(\frac{n_1 + n_2}{2}\right)} + + for :math:`n_1, n_2 > 0`, :math:`\lambda \ge 0`. Here :math:`n_1` is the + degrees of freedom in the numerator, :math:`n_2` the degrees of freedom in + the denominator, :math:`\lambda` the non-centrality parameter, + :math:`\gamma` is the logarithm of the Gamma function, :math:`L_n^k` is a + generalized Laguerre polynomial and :math:`B` is the beta function. + + `ncf` takes ``df1``, ``df2`` and ``nc`` as shape parameters. If ``nc=0``, + the distribution becomes equivalent to the Fisher distribution. + + %(after_notes)s + + %(example)s + + """ + def _argcheck(self, df1, df2, nc): + return (df1 > 0) & (df2 > 0) & (nc >= 0) + + def _shape_info(self): + idf1 = _ShapeInfo("df1", False, (0, np.inf), (False, False)) + idf2 = _ShapeInfo("df2", False, (0, np.inf), (False, False)) + inc = _ShapeInfo("nc", False, (0, np.inf), (True, False)) + return [idf1, idf2, inc] + + def _rvs(self, dfn, dfd, nc, size=None, random_state=None): + return random_state.noncentral_f(dfn, dfd, nc, size) + + def _pdf(self, x, dfn, dfd, nc): + # ncf.pdf(x, df1, df2, nc) = exp(nc/2 + nc*df1*x/(2*(df1*x+df2))) * + # df1**(df1/2) * df2**(df2/2) * x**(df1/2-1) * + # (df2+df1*x)**(-(df1+df2)/2) * + # gamma(df1/2)*gamma(1+df2/2) * + # L^{v1/2-1}^{v2/2}(-nc*v1*x/(2*(v1*x+v2))) / + # (B(v1/2, v2/2) * gamma((v1+v2)/2)) + return _boost._ncf_pdf(x, dfn, dfd, nc) + + def _cdf(self, x, dfn, dfd, nc): + return _boost._ncf_cdf(x, dfn, dfd, nc) + + def _ppf(self, q, dfn, dfd, nc): + with np.errstate(over='ignore'): # see gh-17432 + return _boost._ncf_ppf(q, dfn, dfd, nc) + + def _sf(self, x, dfn, dfd, nc): + return _boost._ncf_sf(x, dfn, dfd, nc) + + def _isf(self, x, dfn, dfd, nc): + with np.errstate(over='ignore'): # see gh-17432 + return _boost._ncf_isf(x, dfn, dfd, nc) + + def _munp(self, n, dfn, dfd, nc): + val = (dfn * 1.0/dfd)**n + term = sc.gammaln(n+0.5*dfn) + sc.gammaln(0.5*dfd-n) - sc.gammaln(dfd*0.5) + val *= np.exp(-nc / 2.0+term) + val *= sc.hyp1f1(n+0.5*dfn, 0.5*dfn, 0.5*nc) + return val + + def _stats(self, dfn, dfd, nc, moments='mv'): + mu = _boost._ncf_mean(dfn, dfd, nc) + mu2 = _boost._ncf_variance(dfn, dfd, nc) + g1 = _boost._ncf_skewness(dfn, dfd, nc) if 's' in moments else None + g2 = _boost._ncf_kurtosis_excess( + dfn, dfd, nc) if 'k' in moments else None + return mu, mu2, g1, g2 + + +ncf = ncf_gen(a=0.0, name='ncf') + + +class t_gen(rv_continuous): + r"""A Student's t continuous random variable. + + For the noncentral t distribution, see `nct`. + + %(before_notes)s + + See Also + -------- + nct + + Notes + ----- + The probability density function for `t` is: + + .. math:: + + f(x, \nu) = \frac{\Gamma((\nu+1)/2)} + {\sqrt{\pi \nu} \Gamma(\nu/2)} + (1+x^2/\nu)^{-(\nu+1)/2} + + where :math:`x` is a real number and the degrees of freedom parameter + :math:`\nu` (denoted ``df`` in the implementation) satisfies + :math:`\nu > 0`. :math:`\Gamma` is the gamma function + (`scipy.special.gamma`). + + %(after_notes)s + + %(example)s + + """ + def _shape_info(self): + return [_ShapeInfo("df", False, (0, np.inf), (False, False))] + + def _rvs(self, df, size=None, random_state=None): + return random_state.standard_t(df, size=size) + + def _pdf(self, x, df): + return _lazywhere( + df == np.inf, (x, df), + f=lambda x, df: norm._pdf(x), + f2=lambda x, df: ( + np.exp(self._logpdf(x, df)) + ) + ) + + def _logpdf(self, x, df): + + def t_logpdf(x, df): + return (np.log(sc.poch(0.5 * df, 0.5)) + - 0.5 * (np.log(df) + np.log(np.pi)) + - (df + 1)/2*np.log1p(x * x/df)) + + def norm_logpdf(x, df): + return norm._logpdf(x) + + return _lazywhere(df == np.inf, (x, df, ), f=norm_logpdf, f2=t_logpdf) + + def _cdf(self, x, df): + return sc.stdtr(df, x) + + def _sf(self, x, df): + return sc.stdtr(df, -x) + + def _ppf(self, q, df): + return sc.stdtrit(df, q) + + def _isf(self, q, df): + return -sc.stdtrit(df, q) + + def _stats(self, df): + # infinite df -> normal distribution (0.0, 1.0, 0.0, 0.0) + infinite_df = np.isposinf(df) + + mu = np.where(df > 1, 0.0, np.inf) + + condlist = ((df > 1) & (df <= 2), + (df > 2) & np.isfinite(df), + infinite_df) + choicelist = (lambda df: np.broadcast_to(np.inf, df.shape), + lambda df: df / (df-2.0), + lambda df: np.broadcast_to(1, df.shape)) + mu2 = _lazyselect(condlist, choicelist, (df,), np.nan) + + g1 = np.where(df > 3, 0.0, np.nan) + + condlist = ((df > 2) & (df <= 4), + (df > 4) & np.isfinite(df), + infinite_df) + choicelist = (lambda df: np.broadcast_to(np.inf, df.shape), + lambda df: 6.0 / (df-4.0), + lambda df: np.broadcast_to(0, df.shape)) + g2 = _lazyselect(condlist, choicelist, (df,), np.nan) + + return mu, mu2, g1, g2 + + def _entropy(self, df): + if df == np.inf: + return norm._entropy() + + def regular(df): + half = df/2 + half1 = (df + 1)/2 + return (half1*(sc.digamma(half1) - sc.digamma(half)) + + np.log(np.sqrt(df)*sc.beta(half, 0.5))) + + def asymptotic(df): + # Formula from Wolfram Alpha: + # "asymptotic expansion (d+1)/2 * (digamma((d+1)/2) - digamma(d/2)) + # + log(sqrt(d) * beta(d/2, 1/2))" + h = (norm._entropy() + 1/df + (df**-2.)/4 - (df**-3.)/6 + - (df**-4.)/8 + 3/10*(df**-5.) + (df**-6.)/4) + return h + + h = _lazywhere(df >= 100, (df, ), f=asymptotic, f2=regular) + return h + + +t = t_gen(name='t') + + +class nct_gen(rv_continuous): + r"""A non-central Student's t continuous random variable. + + %(before_notes)s + + Notes + ----- + If :math:`Y` is a standard normal random variable and :math:`V` is + an independent chi-square random variable (`chi2`) with :math:`k` degrees + of freedom, then + + .. math:: + + X = \frac{Y + c}{\sqrt{V/k}} + + has a non-central Student's t distribution on the real line. + The degrees of freedom parameter :math:`k` (denoted ``df`` in the + implementation) satisfies :math:`k > 0` and the noncentrality parameter + :math:`c` (denoted ``nc`` in the implementation) is a real number. + + %(after_notes)s + + %(example)s + + """ + def _argcheck(self, df, nc): + return (df > 0) & (nc == nc) + + def _shape_info(self): + idf = _ShapeInfo("df", False, (0, np.inf), (False, False)) + inc = _ShapeInfo("nc", False, (-np.inf, np.inf), (False, False)) + return [idf, inc] + + def _rvs(self, df, nc, size=None, random_state=None): + n = norm.rvs(loc=nc, size=size, random_state=random_state) + c2 = chi2.rvs(df, size=size, random_state=random_state) + return n * np.sqrt(df) / np.sqrt(c2) + + def _pdf(self, x, df, nc): + # Boost version has accuracy issues in left tail; see gh-16591 + n = df*1.0 + nc = nc*1.0 + x2 = x*x + ncx2 = nc*nc*x2 + fac1 = n + x2 + trm1 = (n/2.*np.log(n) + sc.gammaln(n+1) + - (n*np.log(2) + nc*nc/2 + (n/2)*np.log(fac1) + + sc.gammaln(n/2))) + Px = np.exp(trm1) + valF = ncx2 / (2*fac1) + trm1 = (np.sqrt(2)*nc*x*sc.hyp1f1(n/2+1, 1.5, valF) + / np.asarray(fac1*sc.gamma((n+1)/2))) + trm2 = (sc.hyp1f1((n+1)/2, 0.5, valF) + / np.asarray(np.sqrt(fac1)*sc.gamma(n/2+1))) + Px *= trm1+trm2 + return np.clip(Px, 0, None) + + def _cdf(self, x, df, nc): + with np.errstate(over='ignore'): # see gh-17432 + return np.clip(_boost._nct_cdf(x, df, nc), 0, 1) + + def _ppf(self, q, df, nc): + with np.errstate(over='ignore'): # see gh-17432 + return _boost._nct_ppf(q, df, nc) + + def _sf(self, x, df, nc): + with np.errstate(over='ignore'): # see gh-17432 + return np.clip(_boost._nct_sf(x, df, nc), 0, 1) + + def _isf(self, x, df, nc): + with np.errstate(over='ignore'): # see gh-17432 + return _boost._nct_isf(x, df, nc) + + def _stats(self, df, nc, moments='mv'): + mu = _boost._nct_mean(df, nc) + mu2 = _boost._nct_variance(df, nc) + g1 = _boost._nct_skewness(df, nc) if 's' in moments else None + g2 = _boost._nct_kurtosis_excess(df, nc) if 'k' in moments else None + return mu, mu2, g1, g2 + + +nct = nct_gen(name="nct") + + +class pareto_gen(rv_continuous): + r"""A Pareto continuous random variable. + + %(before_notes)s + + Notes + ----- + The probability density function for `pareto` is: + + .. math:: + + f(x, b) = \frac{b}{x^{b+1}} + + for :math:`x \ge 1`, :math:`b > 0`. + + `pareto` takes ``b`` as a shape parameter for :math:`b`. + + %(after_notes)s + + %(example)s + + """ + def _shape_info(self): + return [_ShapeInfo("b", False, (0, np.inf), (False, False))] + + def _pdf(self, x, b): + # pareto.pdf(x, b) = b / x**(b+1) + return b * x**(-b-1) + + def _cdf(self, x, b): + return 1 - x**(-b) + + def _ppf(self, q, b): + return pow(1-q, -1.0/b) + + def _sf(self, x, b): + return x**(-b) + + def _isf(self, q, b): + return np.power(q, -1.0 / b) + + def _stats(self, b, moments='mv'): + mu, mu2, g1, g2 = None, None, None, None + if 'm' in moments: + mask = b > 1 + bt = np.extract(mask, b) + mu = np.full(np.shape(b), fill_value=np.inf) + np.place(mu, mask, bt / (bt-1.0)) + if 'v' in moments: + mask = b > 2 + bt = np.extract(mask, b) + mu2 = np.full(np.shape(b), fill_value=np.inf) + np.place(mu2, mask, bt / (bt-2.0) / (bt-1.0)**2) + if 's' in moments: + mask = b > 3 + bt = np.extract(mask, b) + g1 = np.full(np.shape(b), fill_value=np.nan) + vals = 2 * (bt + 1.0) * np.sqrt(bt - 2.0) / ((bt - 3.0) * np.sqrt(bt)) + np.place(g1, mask, vals) + if 'k' in moments: + mask = b > 4 + bt = np.extract(mask, b) + g2 = np.full(np.shape(b), fill_value=np.nan) + vals = (6.0*np.polyval([1.0, 1.0, -6, -2], bt) / + np.polyval([1.0, -7.0, 12.0, 0.0], bt)) + np.place(g2, mask, vals) + return mu, mu2, g1, g2 + + def _entropy(self, c): + return 1 + 1.0/c - np.log(c) + + @_call_super_mom + @inherit_docstring_from(rv_continuous) + def fit(self, data, *args, **kwds): + parameters = _check_fit_input_parameters(self, data, args, kwds) + data, fshape, floc, fscale = parameters + + # ensure that any fixed parameters don't violate constraints of the + # distribution before continuing. + if floc is not None and np.min(data) - floc < (fscale or 0): + raise FitDataError("pareto", lower=1, upper=np.inf) + + ndata = data.shape[0] + + def get_shape(scale, location): + # The first-order necessary condition on `shape` can be solved in + # closed form + return ndata / np.sum(np.log((data - location) / scale)) + + if floc is fscale is None: + # The support of the distribution is `(x - loc)/scale > 0`. + # The method of Lagrange multipliers turns this constraint + # into an equation that can be solved numerically. + # See gh-12545 for details. + + def dL_dScale(shape, scale): + # The partial derivative of the log-likelihood function w.r.t. + # the scale. + return ndata * shape / scale + + def dL_dLocation(shape, location): + # The partial derivative of the log-likelihood function w.r.t. + # the location. + return (shape + 1) * np.sum(1 / (data - location)) + + def fun_to_solve(scale): + # optimize the scale by setting the partial derivatives + # w.r.t. to location and scale equal and solving. + location = np.min(data) - scale + shape = fshape or get_shape(scale, location) + return dL_dLocation(shape, location) - dL_dScale(shape, scale) + + def interval_contains_root(lbrack, rbrack): + # return true if the signs disagree. + return (np.sign(fun_to_solve(lbrack)) != + np.sign(fun_to_solve(rbrack))) + + # set brackets for `root_scalar` to use when optimizing over the + # scale such that a root is likely between them. Use user supplied + # guess or default 1. + brack_start = float(kwds.get('scale', 1)) + lbrack, rbrack = brack_start / 2, brack_start * 2 + # if a root is not between the brackets, iteratively expand them + # until they include a sign change, checking after each bracket is + # modified. + while (not interval_contains_root(lbrack, rbrack) + and (lbrack > 0 or rbrack < np.inf)): + lbrack /= 2 + rbrack *= 2 + res = root_scalar(fun_to_solve, bracket=[lbrack, rbrack]) + if res.converged: + scale = res.root + loc = np.min(data) - scale + shape = fshape or get_shape(scale, loc) + + # The Pareto distribution requires that its parameters satisfy + # the condition `fscale + floc <= min(data)`. However, to + # avoid numerical issues, we require that `fscale + floc` + # is strictly less than `min(data)`. If this condition + # is not satisfied, reduce the scale with `np.nextafter` to + # ensure that data does not fall outside of the support. + if not (scale + loc) < np.min(data): + scale = np.min(data) - loc + scale = np.nextafter(scale, 0) + return shape, loc, scale + else: + return super().fit(data, **kwds) + elif floc is None: + loc = np.min(data) - fscale + else: + loc = floc + # Source: Evans, Hastings, and Peacock (2000), Statistical + # Distributions, 3rd. Ed., John Wiley and Sons. Page 149. + scale = fscale or np.min(data) - loc + shape = fshape or get_shape(scale, loc) + return shape, loc, scale + + +pareto = pareto_gen(a=1.0, name="pareto") + + +class lomax_gen(rv_continuous): + r"""A Lomax (Pareto of the second kind) continuous random variable. + + %(before_notes)s + + Notes + ----- + The probability density function for `lomax` is: + + .. math:: + + f(x, c) = \frac{c}{(1+x)^{c+1}} + + for :math:`x \ge 0`, :math:`c > 0`. + + `lomax` takes ``c`` as a shape parameter for :math:`c`. + + `lomax` is a special case of `pareto` with ``loc=-1.0``. + + %(after_notes)s + + %(example)s + + """ + def _shape_info(self): + return [_ShapeInfo("c", False, (0, np.inf), (False, False))] + + def _pdf(self, x, c): + # lomax.pdf(x, c) = c / (1+x)**(c+1) + return c*1.0/(1.0+x)**(c+1.0) + + def _logpdf(self, x, c): + return np.log(c) - (c+1)*sc.log1p(x) + + def _cdf(self, x, c): + return -sc.expm1(-c*sc.log1p(x)) + + def _sf(self, x, c): + return np.exp(-c*sc.log1p(x)) + + def _logsf(self, x, c): + return -c*sc.log1p(x) + + def _ppf(self, q, c): + return sc.expm1(-sc.log1p(-q)/c) + + def _isf(self, q, c): + return q**(-1.0 / c) - 1 + + def _stats(self, c): + mu, mu2, g1, g2 = pareto.stats(c, loc=-1.0, moments='mvsk') + return mu, mu2, g1, g2 + + def _entropy(self, c): + return 1+1.0/c-np.log(c) + + +lomax = lomax_gen(a=0.0, name="lomax") + + +class pearson3_gen(rv_continuous): + r"""A pearson type III continuous random variable. + + %(before_notes)s + + Notes + ----- + The probability density function for `pearson3` is: + + .. math:: + + f(x, \kappa) = \frac{|\beta|}{\Gamma(\alpha)} + (\beta (x - \zeta))^{\alpha - 1} + \exp(-\beta (x - \zeta)) + + where: + + .. math:: + + \beta = \frac{2}{\kappa} + + \alpha = \beta^2 = \frac{4}{\kappa^2} + + \zeta = -\frac{\alpha}{\beta} = -\beta + + :math:`\Gamma` is the gamma function (`scipy.special.gamma`). + Pass the skew :math:`\kappa` into `pearson3` as the shape parameter + ``skew``. + + %(after_notes)s + + %(example)s + + References + ---------- + R.W. Vogel and D.E. McMartin, "Probability Plot Goodness-of-Fit and + Skewness Estimation Procedures for the Pearson Type 3 Distribution", Water + Resources Research, Vol.27, 3149-3158 (1991). + + L.R. Salvosa, "Tables of Pearson's Type III Function", Ann. Math. Statist., + Vol.1, 191-198 (1930). + + "Using Modern Computing Tools to Fit the Pearson Type III Distribution to + Aviation Loads Data", Office of Aviation Research (2003). + + """ + def _preprocess(self, x, skew): + # The real 'loc' and 'scale' are handled in the calling pdf(...). The + # local variables 'loc' and 'scale' within pearson3._pdf are set to + # the defaults just to keep them as part of the equations for + # documentation. + loc = 0.0 + scale = 1.0 + + # If skew is small, return _norm_pdf. The divide between pearson3 + # and norm was found by brute force and is approximately a skew of + # 0.000016. No one, I hope, would actually use a skew value even + # close to this small. + norm2pearson_transition = 0.000016 + + ans, x, skew = np.broadcast_arrays(1.0, x, skew) + ans = ans.copy() + + # mask is True where skew is small enough to use the normal approx. + mask = np.absolute(skew) < norm2pearson_transition + invmask = ~mask + + beta = 2.0 / (skew[invmask] * scale) + alpha = (scale * beta)**2 + zeta = loc - alpha / beta + + transx = beta * (x[invmask] - zeta) + return ans, x, transx, mask, invmask, beta, alpha, zeta + + def _argcheck(self, skew): + # The _argcheck function in rv_continuous only allows positive + # arguments. The skew argument for pearson3 can be zero (which I want + # to handle inside pearson3._pdf) or negative. So just return True + # for all skew args. + return np.isfinite(skew) + + def _shape_info(self): + return [_ShapeInfo("skew", False, (-np.inf, np.inf), (False, False))] + + def _stats(self, skew): + m = 0.0 + v = 1.0 + s = skew + k = 1.5*skew**2 + return m, v, s, k + + def _pdf(self, x, skew): + # pearson3.pdf(x, skew) = abs(beta) / gamma(alpha) * + # (beta * (x - zeta))**(alpha - 1) * exp(-beta*(x - zeta)) + # Do the calculation in _logpdf since helps to limit + # overflow/underflow problems + ans = np.exp(self._logpdf(x, skew)) + if ans.ndim == 0: + if np.isnan(ans): + return 0.0 + return ans + ans[np.isnan(ans)] = 0.0 + return ans + + def _logpdf(self, x, skew): + # PEARSON3 logpdf GAMMA logpdf + # np.log(abs(beta)) + # + (alpha - 1)*np.log(beta*(x - zeta)) + (a - 1)*np.log(x) + # - beta*(x - zeta) - x + # - sc.gammalnalpha) - sc.gammalna) + ans, x, transx, mask, invmask, beta, alpha, _ = ( + self._preprocess(x, skew)) + + ans[mask] = np.log(_norm_pdf(x[mask])) + # use logpdf instead of _logpdf to fix issue mentioned in gh-12640 + # (_logpdf does not return correct result for alpha = 1) + ans[invmask] = np.log(abs(beta)) + gamma.logpdf(transx, alpha) + return ans + + def _cdf(self, x, skew): + ans, x, transx, mask, invmask, _, alpha, _ = ( + self._preprocess(x, skew)) + + ans[mask] = _norm_cdf(x[mask]) + + skew = np.broadcast_to(skew, invmask.shape) + invmask1a = np.logical_and(invmask, skew > 0) + invmask1b = skew[invmask] > 0 + # use cdf instead of _cdf to fix issue mentioned in gh-12640 + # (_cdf produces NaNs for inputs outside support) + ans[invmask1a] = gamma.cdf(transx[invmask1b], alpha[invmask1b]) + + # The gamma._cdf approach wasn't working with negative skew. + # Note that multiplying the skew by -1 reflects about x=0. + # So instead of evaluating the CDF with negative skew at x, + # evaluate the SF with positive skew at -x. + invmask2a = np.logical_and(invmask, skew < 0) + invmask2b = skew[invmask] < 0 + # gamma._sf produces NaNs when transx < 0, so use gamma.sf + ans[invmask2a] = gamma.sf(transx[invmask2b], alpha[invmask2b]) + + return ans + + def _sf(self, x, skew): + ans, x, transx, mask, invmask, _, alpha, _ = ( + self._preprocess(x, skew)) + + ans[mask] = _norm_sf(x[mask]) + + skew = np.broadcast_to(skew, invmask.shape) + invmask1a = np.logical_and(invmask, skew > 0) + invmask1b = skew[invmask] > 0 + ans[invmask1a] = gamma.sf(transx[invmask1b], alpha[invmask1b]) + + invmask2a = np.logical_and(invmask, skew < 0) + invmask2b = skew[invmask] < 0 + ans[invmask2a] = gamma.cdf(transx[invmask2b], alpha[invmask2b]) + + return ans + + def _rvs(self, skew, size=None, random_state=None): + skew = np.broadcast_to(skew, size) + ans, _, _, mask, invmask, beta, alpha, zeta = ( + self._preprocess([0], skew)) + + nsmall = mask.sum() + nbig = mask.size - nsmall + ans[mask] = random_state.standard_normal(nsmall) + ans[invmask] = random_state.standard_gamma(alpha, nbig)/beta + zeta + + if size == (): + ans = ans[0] + return ans + + def _ppf(self, q, skew): + ans, q, _, mask, invmask, beta, alpha, zeta = ( + self._preprocess(q, skew)) + ans[mask] = _norm_ppf(q[mask]) + q = q[invmask] + q[beta < 0] = 1 - q[beta < 0] # for negative skew; see gh-17050 + ans[invmask] = sc.gammaincinv(alpha, q)/beta + zeta + return ans + + @_call_super_mom + @extend_notes_in_docstring(rv_continuous, notes="""\ + Note that method of moments (`method='MM'`) is not + available for this distribution.\n\n""") + def fit(self, data, *args, **kwds): + if kwds.get("method", None) == 'MM': + raise NotImplementedError("Fit `method='MM'` is not available for " + "the Pearson3 distribution. Please try " + "the default `method='MLE'`.") + else: + return super(type(self), self).fit(data, *args, **kwds) + + +pearson3 = pearson3_gen(name="pearson3") + + +class powerlaw_gen(rv_continuous): + r"""A power-function continuous random variable. + + %(before_notes)s + + See Also + -------- + pareto + + Notes + ----- + The probability density function for `powerlaw` is: + + .. math:: + + f(x, a) = a x^{a-1} + + for :math:`0 \le x \le 1`, :math:`a > 0`. + + `powerlaw` takes ``a`` as a shape parameter for :math:`a`. + + %(after_notes)s + + For example, the support of `powerlaw` can be adjusted from the default + interval ``[0, 1]`` to the interval ``[c, c+d]`` by setting ``loc=c`` and + ``scale=d``. For a power-law distribution with infinite support, see + `pareto`. + + `powerlaw` is a special case of `beta` with ``b=1``. + + %(example)s + + """ + def _shape_info(self): + return [_ShapeInfo("a", False, (0, np.inf), (False, False))] + + def _pdf(self, x, a): + # powerlaw.pdf(x, a) = a * x**(a-1) + return a*x**(a-1.0) + + def _logpdf(self, x, a): + return np.log(a) + sc.xlogy(a - 1, x) + + def _cdf(self, x, a): + return x**(a*1.0) + + def _logcdf(self, x, a): + return a*np.log(x) + + def _ppf(self, q, a): + return pow(q, 1.0/a) + + def _sf(self, p, a): + return -sc.powm1(p, a) + + def _munp(self, n, a): + # The following expression is correct for all real n (provided a > 0). + return a / (a + n) + + def _stats(self, a): + return (a / (a + 1.0), + a / (a + 2.0) / (a + 1.0) ** 2, + -2.0 * ((a - 1.0) / (a + 3.0)) * np.sqrt((a + 2.0) / a), + 6 * np.polyval([1, -1, -6, 2], a) / (a * (a + 3.0) * (a + 4))) + + def _entropy(self, a): + return 1 - 1.0/a - np.log(a) + + def _support_mask(self, x, a): + return (super()._support_mask(x, a) + & ((x != 0) | (a >= 1))) + + @_call_super_mom + @extend_notes_in_docstring(rv_continuous, notes="""\ + Notes specifically for ``powerlaw.fit``: If the location is a free + parameter and the value returned for the shape parameter is less than + one, the true maximum likelihood approaches infinity. This causes + numerical difficulties, and the resulting estimates are approximate. + \n\n""") + def fit(self, data, *args, **kwds): + # Summary of the strategy: + # + # 1) If the scale and location are fixed, return the shape according + # to a formula. + # + # 2) If the scale is fixed, there are two possibilities for the other + # parameters - one corresponding with shape less than one, and + # another with shape greater than one. Calculate both, and return + # whichever has the better log-likelihood. + # + # At this point, the scale is known to be free. + # + # 3) If the location is fixed, return the scale and shape according to + # formulas (or, if the shape is fixed, the fixed shape). + # + # At this point, the location and scale are both free. There are + # separate equations depending on whether the shape is less than one or + # greater than one. + # + # 4a) If the shape is less than one, there are formulas for shape, + # location, and scale. + # 4b) If the shape is greater than one, there are formulas for shape + # and scale, but there is a condition for location to be solved + # numerically. + # + # If the shape is fixed and less than one, we use 4a. + # If the shape is fixed and greater than one, we use 4b. + # If the shape is also free, we calculate fits using both 4a and 4b + # and choose the one that results a better log-likelihood. + # + # In many cases, the use of `np.nextafter` is used to avoid numerical + # issues. + if kwds.pop('superfit', False): + return super().fit(data, *args, **kwds) + + if len(np.unique(data)) == 1: + return super().fit(data, *args, **kwds) + + data, fshape, floc, fscale = _check_fit_input_parameters(self, data, + args, kwds) + penalized_nllf_args = [data, (self._fitstart(data),)] + penalized_nllf = self._reduce_func(penalized_nllf_args, {})[1] + + # ensure that any fixed parameters don't violate constraints of the + # distribution before continuing. The support of the distribution + # is `0 < (x - loc)/scale < 1`. + if floc is not None: + if not data.min() > floc: + raise FitDataError('powerlaw', 0, 1) + if fscale is not None and not data.max() <= floc + fscale: + raise FitDataError('powerlaw', 0, 1) + + if fscale is not None: + if fscale <= 0: + raise ValueError("Negative or zero `fscale` is outside the " + "range allowed by the distribution.") + if fscale <= np.ptp(data): + msg = "`fscale` must be greater than the range of data." + raise ValueError(msg) + + def get_shape(data, loc, scale): + # The first-order necessary condition on `shape` can be solved in + # closed form. It can be used no matter the assumption of the + # value of the shape. + N = len(data) + return - N / (np.sum(np.log(data - loc)) - N*np.log(scale)) + + def get_scale(data, loc): + # analytical solution for `scale` based on the location. + # It can be used no matter the assumption of the value of the + # shape. + return data.max() - loc + + # 1) The location and scale are both fixed. Analytically determine the + # shape. + if fscale is not None and floc is not None: + return get_shape(data, floc, fscale), floc, fscale + + # 2) The scale is fixed. There are two possibilities for the other + # parameters. Choose the option with better log-likelihood. + if fscale is not None: + # using `data.min()` as the optimal location + loc_lt1 = np.nextafter(data.min(), -np.inf) + shape_lt1 = fshape or get_shape(data, loc_lt1, fscale) + ll_lt1 = penalized_nllf((shape_lt1, loc_lt1, fscale), data) + + # using `data.max() - scale` as the optimal location + loc_gt1 = np.nextafter(data.max() - fscale, np.inf) + shape_gt1 = fshape or get_shape(data, loc_gt1, fscale) + ll_gt1 = penalized_nllf((shape_gt1, loc_gt1, fscale), data) + + if ll_lt1 < ll_gt1: + return shape_lt1, loc_lt1, fscale + else: + return shape_gt1, loc_gt1, fscale + + # 3) The location is fixed. Return the analytical scale and the + # analytical (or fixed) shape. + if floc is not None: + scale = get_scale(data, floc) + shape = fshape or get_shape(data, floc, scale) + return shape, floc, scale + + # 4) Location and scale are both free + # 4a) Use formulas that assume `shape <= 1`. + + def fit_loc_scale_w_shape_lt_1(): + loc = np.nextafter(data.min(), -np.inf) + if np.abs(loc) < np.finfo(loc.dtype).tiny: + loc = np.sign(loc) * np.finfo(loc.dtype).tiny + scale = np.nextafter(get_scale(data, loc), np.inf) + shape = fshape or get_shape(data, loc, scale) + return shape, loc, scale + + # 4b) Fit under the assumption that `shape > 1`. The support + # of the distribution is `(x - loc)/scale <= 1`. The method of Lagrange + # multipliers turns this constraint into the condition that + # dL_dScale - dL_dLocation must be zero, which is solved numerically. + # (Alternatively, substitute the constraint into the objective + # function before deriving the likelihood equation for location.) + + def dL_dScale(data, shape, scale): + # The partial derivative of the log-likelihood function w.r.t. + # the scale. + return -data.shape[0] * shape / scale + + def dL_dLocation(data, shape, loc): + # The partial derivative of the log-likelihood function w.r.t. + # the location. + return (shape - 1) * np.sum(1 / (loc - data)) # -1/(data-loc) + + def dL_dLocation_star(loc): + # The derivative of the log-likelihood function w.r.t. + # the location, given optimal shape and scale + scale = np.nextafter(get_scale(data, loc), -np.inf) + shape = fshape or get_shape(data, loc, scale) + return dL_dLocation(data, shape, loc) + + def fun_to_solve(loc): + # optimize the location by setting the partial derivatives + # w.r.t. to location and scale equal and solving. + scale = np.nextafter(get_scale(data, loc), -np.inf) + shape = fshape or get_shape(data, loc, scale) + return (dL_dScale(data, shape, scale) + - dL_dLocation(data, shape, loc)) + + def fit_loc_scale_w_shape_gt_1(): + # set brackets for `root_scalar` to use when optimizing over the + # location such that a root is likely between them. + rbrack = np.nextafter(data.min(), -np.inf) + + # if the sign of `dL_dLocation_star` is positive at rbrack, + # we're not going to find the root we're looking for + delta = (data.min() - rbrack) + while dL_dLocation_star(rbrack) > 0: + rbrack = data.min() - delta + delta *= 2 + + def interval_contains_root(lbrack, rbrack): + # Check if the interval (lbrack, rbrack) contains the root. + return (np.sign(fun_to_solve(lbrack)) + != np.sign(fun_to_solve(rbrack))) + + lbrack = rbrack - 1 + + # if the sign doesn't change between the brackets, move the left + # bracket until it does. (The right bracket remains fixed at the + # maximum permissible value.) + i = 1.0 + while (not interval_contains_root(lbrack, rbrack) + and lbrack != -np.inf): + lbrack = (data.min() - i) + i *= 2 + + root = optimize.root_scalar(fun_to_solve, bracket=(lbrack, rbrack)) + + loc = np.nextafter(root.root, -np.inf) + scale = np.nextafter(get_scale(data, loc), np.inf) + shape = fshape or get_shape(data, loc, scale) + return shape, loc, scale + + # Shape is fixed - choose 4a or 4b accordingly. + if fshape is not None and fshape <= 1: + return fit_loc_scale_w_shape_lt_1() + elif fshape is not None and fshape > 1: + return fit_loc_scale_w_shape_gt_1() + + # Shape is free + fit_shape_lt1 = fit_loc_scale_w_shape_lt_1() + ll_lt1 = self.nnlf(fit_shape_lt1, data) + + fit_shape_gt1 = fit_loc_scale_w_shape_gt_1() + ll_gt1 = self.nnlf(fit_shape_gt1, data) + + if ll_lt1 <= ll_gt1 and fit_shape_lt1[0] <= 1: + return fit_shape_lt1 + elif ll_lt1 > ll_gt1 and fit_shape_gt1[0] > 1: + return fit_shape_gt1 + else: + return super().fit(data, *args, **kwds) + + +powerlaw = powerlaw_gen(a=0.0, b=1.0, name="powerlaw") + + +class powerlognorm_gen(rv_continuous): + r"""A power log-normal continuous random variable. + + %(before_notes)s + + Notes + ----- + The probability density function for `powerlognorm` is: + + .. math:: + + f(x, c, s) = \frac{c}{x s} \phi(\log(x)/s) + (\Phi(-\log(x)/s))^{c-1} + + where :math:`\phi` is the normal pdf, and :math:`\Phi` is the normal cdf, + and :math:`x > 0`, :math:`s, c > 0`. + + `powerlognorm` takes :math:`c` and :math:`s` as shape parameters. + + %(after_notes)s + + %(example)s + + """ + _support_mask = rv_continuous._open_support_mask + + def _shape_info(self): + ic = _ShapeInfo("c", False, (0, np.inf), (False, False)) + i_s = _ShapeInfo("s", False, (0, np.inf), (False, False)) + return [ic, i_s] + + def _pdf(self, x, c, s): + return np.exp(self._logpdf(x, c, s)) + + def _logpdf(self, x, c, s): + return (np.log(c) - np.log(x) - np.log(s) + + _norm_logpdf(np.log(x) / s) + + _norm_logcdf(-np.log(x) / s) * (c - 1.)) + + def _cdf(self, x, c, s): + return -sc.expm1(self._logsf(x, c, s)) + + def _ppf(self, q, c, s): + return self._isf(1 - q, c, s) + + def _sf(self, x, c, s): + return np.exp(self._logsf(x, c, s)) + + def _logsf(self, x, c, s): + return _norm_logcdf(-np.log(x) / s) * c + + def _isf(self, q, c, s): + return np.exp(-_norm_ppf(q**(1/c)) * s) + + +powerlognorm = powerlognorm_gen(a=0.0, name="powerlognorm") + + +class powernorm_gen(rv_continuous): + r"""A power normal continuous random variable. + + %(before_notes)s + + Notes + ----- + The probability density function for `powernorm` is: + + .. math:: + + f(x, c) = c \phi(x) (\Phi(-x))^{c-1} + + where :math:`\phi` is the normal pdf, :math:`\Phi` is the normal cdf, + :math:`x` is any real, and :math:`c > 0` [1]_. + + `powernorm` takes ``c`` as a shape parameter for :math:`c`. + + %(after_notes)s + + References + ---------- + .. [1] NIST Engineering Statistics Handbook, Section 1.3.6.6.13, + https://www.itl.nist.gov/div898/handbook//eda/section3/eda366d.htm + + %(example)s + + """ + def _shape_info(self): + return [_ShapeInfo("c", False, (0, np.inf), (False, False))] + + def _pdf(self, x, c): + # powernorm.pdf(x, c) = c * phi(x) * (Phi(-x))**(c-1) + return c*_norm_pdf(x) * (_norm_cdf(-x)**(c-1.0)) + + def _logpdf(self, x, c): + return np.log(c) + _norm_logpdf(x) + (c-1)*_norm_logcdf(-x) + + def _cdf(self, x, c): + return -sc.expm1(self._logsf(x, c)) + + def _ppf(self, q, c): + return -_norm_ppf(pow(1.0 - q, 1.0 / c)) + + def _sf(self, x, c): + return np.exp(self._logsf(x, c)) + + def _logsf(self, x, c): + return c * _norm_logcdf(-x) + + def _isf(self, q, c): + return -_norm_ppf(np.exp(np.log(q) / c)) + + +powernorm = powernorm_gen(name='powernorm') + + +class rdist_gen(rv_continuous): + r"""An R-distributed (symmetric beta) continuous random variable. + + %(before_notes)s + + Notes + ----- + The probability density function for `rdist` is: + + .. math:: + + f(x, c) = \frac{(1-x^2)^{c/2-1}}{B(1/2, c/2)} + + for :math:`-1 \le x \le 1`, :math:`c > 0`. `rdist` is also called the + symmetric beta distribution: if B has a `beta` distribution with + parameters (c/2, c/2), then X = 2*B - 1 follows a R-distribution with + parameter c. + + `rdist` takes ``c`` as a shape parameter for :math:`c`. + + This distribution includes the following distribution kernels as + special cases:: + + c = 2: uniform + c = 3: `semicircular` + c = 4: Epanechnikov (parabolic) + c = 6: quartic (biweight) + c = 8: triweight + + %(after_notes)s + + %(example)s + + """ + def _shape_info(self): + return [_ShapeInfo("c", False, (0, np.inf), (False, False))] + + # use relation to the beta distribution for pdf, cdf, etc + def _pdf(self, x, c): + return np.exp(self._logpdf(x, c)) + + def _logpdf(self, x, c): + return -np.log(2) + beta._logpdf((x + 1)/2, c/2, c/2) + + def _cdf(self, x, c): + return beta._cdf((x + 1)/2, c/2, c/2) + + def _sf(self, x, c): + return beta._sf((x + 1)/2, c/2, c/2) + + def _ppf(self, q, c): + return 2*beta._ppf(q, c/2, c/2) - 1 + + def _rvs(self, c, size=None, random_state=None): + return 2 * random_state.beta(c/2, c/2, size) - 1 + + def _munp(self, n, c): + numerator = (1 - (n % 2)) * sc.beta((n + 1.0) / 2, c / 2.0) + return numerator / sc.beta(1. / 2, c / 2.) + + +rdist = rdist_gen(a=-1.0, b=1.0, name="rdist") + + +class rayleigh_gen(rv_continuous): + r"""A Rayleigh continuous random variable. + + %(before_notes)s + + Notes + ----- + The probability density function for `rayleigh` is: + + .. math:: + + f(x) = x \exp(-x^2/2) + + for :math:`x \ge 0`. + + `rayleigh` is a special case of `chi` with ``df=2``. + + %(after_notes)s + + %(example)s + + """ + _support_mask = rv_continuous._open_support_mask + + def _shape_info(self): + return [] + + def _rvs(self, size=None, random_state=None): + return chi.rvs(2, size=size, random_state=random_state) + + def _pdf(self, r): + # rayleigh.pdf(r) = r * exp(-r**2/2) + return np.exp(self._logpdf(r)) + + def _logpdf(self, r): + return np.log(r) - 0.5 * r * r + + def _cdf(self, r): + return -sc.expm1(-0.5 * r**2) + + def _ppf(self, q): + return np.sqrt(-2 * sc.log1p(-q)) + + def _sf(self, r): + return np.exp(self._logsf(r)) + + def _logsf(self, r): + return -0.5 * r * r + + def _isf(self, q): + return np.sqrt(-2 * np.log(q)) + + def _stats(self): + val = 4 - np.pi + return (np.sqrt(np.pi/2), + val/2, + 2*(np.pi-3)*np.sqrt(np.pi)/val**1.5, + 6*np.pi/val-16/val**2) + + def _entropy(self): + return _EULER/2.0 + 1 - 0.5*np.log(2) + + @_call_super_mom + @extend_notes_in_docstring(rv_continuous, notes="""\ + Notes specifically for ``rayleigh.fit``: If the location is fixed with + the `floc` parameter, this method uses an analytical formula to find + the scale. Otherwise, this function uses a numerical root finder on + the first order conditions of the log-likelihood function to find the + MLE. Only the (optional) `loc` parameter is used as the initial guess + for the root finder; the `scale` parameter and any other parameters + for the optimizer are ignored.\n\n""") + def fit(self, data, *args, **kwds): + if kwds.pop('superfit', False): + return super().fit(data, *args, **kwds) + data, floc, fscale = _check_fit_input_parameters(self, data, + args, kwds) + + def scale_mle(loc): + # Source: Statistical Distributions, 3rd Edition. Evans, Hastings, + # and Peacock (2000), Page 175 + return (np.sum((data - loc) ** 2) / (2 * len(data))) ** .5 + + def loc_mle(loc): + # This implicit equation for `loc` is used when + # both `loc` and `scale` are free. + xm = data - loc + s1 = xm.sum() + s2 = (xm**2).sum() + s3 = (1/xm).sum() + return s1 - s2/(2*len(data))*s3 + + def loc_mle_scale_fixed(loc, scale=fscale): + # This implicit equation for `loc` is used when + # `scale` is fixed but `loc` is not. + xm = data - loc + return xm.sum() - scale**2 * (1/xm).sum() + + if floc is not None: + # `loc` is fixed, analytically determine `scale`. + if np.any(data - floc <= 0): + raise FitDataError("rayleigh", lower=1, upper=np.inf) + else: + return floc, scale_mle(floc) + + # Account for user provided guess of `loc`. + loc0 = kwds.get('loc') + if loc0 is None: + # Use _fitstart to estimate loc; ignore the returned scale. + loc0 = self._fitstart(data)[0] + + fun = loc_mle if fscale is None else loc_mle_scale_fixed + rbrack = np.nextafter(np.min(data), -np.inf) + lbrack = _get_left_bracket(fun, rbrack) + res = optimize.root_scalar(fun, bracket=(lbrack, rbrack)) + if not res.converged: + raise FitSolverError(res.flag) + loc = res.root + scale = fscale or scale_mle(loc) + return loc, scale + + +rayleigh = rayleigh_gen(a=0.0, name="rayleigh") + + +class reciprocal_gen(rv_continuous): + r"""A loguniform or reciprocal continuous random variable. + + %(before_notes)s + + Notes + ----- + The probability density function for this class is: + + .. math:: + + f(x, a, b) = \frac{1}{x \log(b/a)} + + for :math:`a \le x \le b`, :math:`b > a > 0`. This class takes + :math:`a` and :math:`b` as shape parameters. + + %(after_notes)s + + %(example)s + + This doesn't show the equal probability of ``0.01``, ``0.1`` and + ``1``. This is best when the x-axis is log-scaled: + + >>> import numpy as np + >>> import matplotlib.pyplot as plt + >>> fig, ax = plt.subplots(1, 1) + >>> ax.hist(np.log10(r)) + >>> ax.set_ylabel("Frequency") + >>> ax.set_xlabel("Value of random variable") + >>> ax.xaxis.set_major_locator(plt.FixedLocator([-2, -1, 0])) + >>> ticks = ["$10^{{ {} }}$".format(i) for i in [-2, -1, 0]] + >>> ax.set_xticklabels(ticks) # doctest: +SKIP + >>> plt.show() + + This random variable will be log-uniform regardless of the base chosen for + ``a`` and ``b``. Let's specify with base ``2`` instead: + + >>> rvs = %(name)s(2**-2, 2**0).rvs(size=1000) + + Values of ``1/4``, ``1/2`` and ``1`` are equally likely with this random + variable. Here's the histogram: + + >>> fig, ax = plt.subplots(1, 1) + >>> ax.hist(np.log2(rvs)) + >>> ax.set_ylabel("Frequency") + >>> ax.set_xlabel("Value of random variable") + >>> ax.xaxis.set_major_locator(plt.FixedLocator([-2, -1, 0])) + >>> ticks = ["$2^{{ {} }}$".format(i) for i in [-2, -1, 0]] + >>> ax.set_xticklabels(ticks) # doctest: +SKIP + >>> plt.show() + + """ + def _argcheck(self, a, b): + return (a > 0) & (b > a) + + def _shape_info(self): + ia = _ShapeInfo("a", False, (0, np.inf), (False, False)) + ib = _ShapeInfo("b", False, (0, np.inf), (False, False)) + return [ia, ib] + + def _fitstart(self, data): + if isinstance(data, CensoredData): + data = data._uncensor() + # Reasonable, since support is [a, b] + return super()._fitstart(data, args=(np.min(data), np.max(data))) + + def _get_support(self, a, b): + return a, b + + def _pdf(self, x, a, b): + # reciprocal.pdf(x, a, b) = 1 / (x*(log(b) - log(a))) + return np.exp(self._logpdf(x, a, b)) + + def _logpdf(self, x, a, b): + return -np.log(x) - np.log(np.log(b) - np.log(a)) + + def _cdf(self, x, a, b): + return (np.log(x)-np.log(a)) / (np.log(b) - np.log(a)) + + def _ppf(self, q, a, b): + return np.exp(np.log(a) + q*(np.log(b) - np.log(a))) + + def _munp(self, n, a, b): + t1 = 1 / (np.log(b) - np.log(a)) / n + t2 = np.real(np.exp(_log_diff(n * np.log(b), n*np.log(a)))) + return t1 * t2 + + def _entropy(self, a, b): + return 0.5*(np.log(a) + np.log(b)) + np.log(np.log(b) - np.log(a)) + + fit_note = """\ + `loguniform`/`reciprocal` is over-parameterized. `fit` automatically + fixes `scale` to 1 unless `fscale` is provided by the user.\n\n""" + + @extend_notes_in_docstring(rv_continuous, notes=fit_note) + def fit(self, data, *args, **kwds): + fscale = kwds.pop('fscale', 1) + return super().fit(data, *args, fscale=fscale, **kwds) + + # Details related to the decision of not defining + # the survival function for this distribution can be + # found in the PR: https://github.com/scipy/scipy/pull/18614 + + +loguniform = reciprocal_gen(name="loguniform") +reciprocal = reciprocal_gen(name="reciprocal") + + +class rice_gen(rv_continuous): + r"""A Rice continuous random variable. + + %(before_notes)s + + Notes + ----- + The probability density function for `rice` is: + + .. math:: + + f(x, b) = x \exp(- \frac{x^2 + b^2}{2}) I_0(x b) + + for :math:`x >= 0`, :math:`b > 0`. :math:`I_0` is the modified Bessel + function of order zero (`scipy.special.i0`). + + `rice` takes ``b`` as a shape parameter for :math:`b`. + + %(after_notes)s + + The Rice distribution describes the length, :math:`r`, of a 2-D vector with + components :math:`(U+u, V+v)`, where :math:`U, V` are constant, :math:`u, + v` are independent Gaussian random variables with standard deviation + :math:`s`. Let :math:`R = \sqrt{U^2 + V^2}`. Then the pdf of :math:`r` is + ``rice.pdf(x, R/s, scale=s)``. + + %(example)s + + """ + def _argcheck(self, b): + return b >= 0 + + def _shape_info(self): + return [_ShapeInfo("b", False, (0, np.inf), (True, False))] + + def _rvs(self, b, size=None, random_state=None): + # https://en.wikipedia.org/wiki/Rice_distribution + t = b/np.sqrt(2) + random_state.standard_normal(size=(2,) + size) + return np.sqrt((t*t).sum(axis=0)) + + def _cdf(self, x, b): + return sc.chndtr(np.square(x), 2, np.square(b)) + + def _ppf(self, q, b): + return np.sqrt(sc.chndtrix(q, 2, np.square(b))) + + def _pdf(self, x, b): + # rice.pdf(x, b) = x * exp(-(x**2+b**2)/2) * I[0](x*b) + # + # We use (x**2 + b**2)/2 = ((x-b)**2)/2 + xb. + # The factor of np.exp(-xb) is then included in the i0e function + # in place of the modified Bessel function, i0, improving + # numerical stability for large values of xb. + return x * np.exp(-(x-b)*(x-b)/2.0) * sc.i0e(x*b) + + def _munp(self, n, b): + nd2 = n/2.0 + n1 = 1 + nd2 + b2 = b*b/2.0 + return (2.0**(nd2) * np.exp(-b2) * sc.gamma(n1) * + sc.hyp1f1(n1, 1, b2)) + + +rice = rice_gen(a=0.0, name="rice") + + +class recipinvgauss_gen(rv_continuous): + r"""A reciprocal inverse Gaussian continuous random variable. + + %(before_notes)s + + Notes + ----- + The probability density function for `recipinvgauss` is: + + .. math:: + + f(x, \mu) = \frac{1}{\sqrt{2\pi x}} + \exp\left(\frac{-(1-\mu x)^2}{2\mu^2x}\right) + + for :math:`x \ge 0`. + + `recipinvgauss` takes ``mu`` as a shape parameter for :math:`\mu`. + + %(after_notes)s + + %(example)s + + """ + def _shape_info(self): + return [_ShapeInfo("mu", False, (0, np.inf), (False, False))] + + def _pdf(self, x, mu): + # recipinvgauss.pdf(x, mu) = + # 1/sqrt(2*pi*x) * exp(-(1-mu*x)**2/(2*x*mu**2)) + return np.exp(self._logpdf(x, mu)) + + def _logpdf(self, x, mu): + return _lazywhere(x > 0, (x, mu), + lambda x, mu: (-(1 - mu*x)**2.0 / (2*x*mu**2.0) + - 0.5*np.log(2*np.pi*x)), + fillvalue=-np.inf) + + def _cdf(self, x, mu): + trm1 = 1.0/mu - x + trm2 = 1.0/mu + x + isqx = 1.0/np.sqrt(x) + return _norm_cdf(-isqx*trm1) - np.exp(2.0/mu)*_norm_cdf(-isqx*trm2) + + def _sf(self, x, mu): + trm1 = 1.0/mu - x + trm2 = 1.0/mu + x + isqx = 1.0/np.sqrt(x) + return _norm_cdf(isqx*trm1) + np.exp(2.0/mu)*_norm_cdf(-isqx*trm2) + + def _rvs(self, mu, size=None, random_state=None): + return 1.0/random_state.wald(mu, 1.0, size=size) + + +recipinvgauss = recipinvgauss_gen(a=0.0, name='recipinvgauss') + + +class semicircular_gen(rv_continuous): + r"""A semicircular continuous random variable. + + %(before_notes)s + + See Also + -------- + rdist + + Notes + ----- + The probability density function for `semicircular` is: + + .. math:: + + f(x) = \frac{2}{\pi} \sqrt{1-x^2} + + for :math:`-1 \le x \le 1`. + + The distribution is a special case of `rdist` with `c = 3`. + + %(after_notes)s + + References + ---------- + .. [1] "Wigner semicircle distribution", + https://en.wikipedia.org/wiki/Wigner_semicircle_distribution + + %(example)s + + """ + def _shape_info(self): + return [] + + def _pdf(self, x): + return 2.0/np.pi*np.sqrt(1-x*x) + + def _logpdf(self, x): + return np.log(2/np.pi) + 0.5*sc.log1p(-x*x) + + def _cdf(self, x): + return 0.5+1.0/np.pi*(x*np.sqrt(1-x*x) + np.arcsin(x)) + + def _ppf(self, q): + return rdist._ppf(q, 3) + + def _rvs(self, size=None, random_state=None): + # generate values uniformly distributed on the area under the pdf + # (semi-circle) by randomly generating the radius and angle + r = np.sqrt(random_state.uniform(size=size)) + a = np.cos(np.pi * random_state.uniform(size=size)) + return r * a + + def _stats(self): + return 0, 0.25, 0, -1.0 + + def _entropy(self): + return 0.64472988584940017414 + + +semicircular = semicircular_gen(a=-1.0, b=1.0, name="semicircular") + + +class skewcauchy_gen(rv_continuous): + r"""A skewed Cauchy random variable. + + %(before_notes)s + + See Also + -------- + cauchy : Cauchy distribution + + Notes + ----- + + The probability density function for `skewcauchy` is: + + .. math:: + + f(x) = \frac{1}{\pi \left(\frac{x^2}{\left(a\, \text{sign}(x) + 1 + \right)^2} + 1 \right)} + + for a real number :math:`x` and skewness parameter :math:`-1 < a < 1`. + + When :math:`a=0`, the distribution reduces to the usual Cauchy + distribution. + + %(after_notes)s + + References + ---------- + .. [1] "Skewed generalized *t* distribution", Wikipedia + https://en.wikipedia.org/wiki/Skewed_generalized_t_distribution#Skewed_Cauchy_distribution + + %(example)s + + """ + def _argcheck(self, a): + return np.abs(a) < 1 + + def _shape_info(self): + return [_ShapeInfo("a", False, (-1.0, 1.0), (False, False))] + + def _pdf(self, x, a): + return 1 / (np.pi * (x**2 / (a * np.sign(x) + 1)**2 + 1)) + + def _cdf(self, x, a): + return np.where(x <= 0, + (1 - a) / 2 + (1 - a) / np.pi * np.arctan(x / (1 - a)), + (1 - a) / 2 + (1 + a) / np.pi * np.arctan(x / (1 + a))) + + def _ppf(self, x, a): + i = x < self._cdf(0, a) + return np.where(i, + np.tan(np.pi / (1 - a) * (x - (1 - a) / 2)) * (1 - a), + np.tan(np.pi / (1 + a) * (x - (1 - a) / 2)) * (1 + a)) + + def _stats(self, a, moments='mvsk'): + return np.nan, np.nan, np.nan, np.nan + + def _fitstart(self, data): + # Use 0 as the initial guess of the skewness shape parameter. + # For the location and scale, estimate using the median and + # quartiles. + if isinstance(data, CensoredData): + data = data._uncensor() + p25, p50, p75 = np.percentile(data, [25, 50, 75]) + return 0.0, p50, (p75 - p25)/2 + + +skewcauchy = skewcauchy_gen(name='skewcauchy') + + +class skewnorm_gen(rv_continuous): + r"""A skew-normal random variable. + + %(before_notes)s + + Notes + ----- + The pdf is:: + + skewnorm.pdf(x, a) = 2 * norm.pdf(x) * norm.cdf(a*x) + + `skewnorm` takes a real number :math:`a` as a skewness parameter + When ``a = 0`` the distribution is identical to a normal distribution + (`norm`). `rvs` implements the method of [1]_. + + %(after_notes)s + + %(example)s + + References + ---------- + .. [1] A. Azzalini and A. Capitanio (1999). Statistical applications of + the multivariate skew-normal distribution. J. Roy. Statist. Soc., + B 61, 579-602. :arxiv:`0911.2093` + + """ + def _argcheck(self, a): + return np.isfinite(a) + + def _shape_info(self): + return [_ShapeInfo("a", False, (-np.inf, np.inf), (False, False))] + + def _pdf(self, x, a): + return _lazywhere( + a == 0, (x, a), lambda x, a: _norm_pdf(x), + f2=lambda x, a: 2.*_norm_pdf(x)*_norm_cdf(a*x) + ) + + def _logpdf(self, x, a): + return _lazywhere( + a == 0, (x, a), lambda x, a: _norm_logpdf(x), + f2=lambda x, a: np.log(2)+_norm_logpdf(x)+_norm_logcdf(a*x), + ) + + def _cdf(self, x, a): + a = np.atleast_1d(a) + cdf = _boost._skewnorm_cdf(x, 0, 1, a) + # for some reason, a isn't broadcasted if some of x are invalid + a = np.broadcast_to(a, cdf.shape) + # Boost is not accurate in left tail when a > 0 + i_small_cdf = (cdf < 1e-6) & (a > 0) + cdf[i_small_cdf] = super()._cdf(x[i_small_cdf], a[i_small_cdf]) + return np.clip(cdf, 0, 1) + + def _ppf(self, x, a): + return _boost._skewnorm_ppf(x, 0, 1, a) + + def _sf(self, x, a): + # Boost's SF is implemented this way. Use whatever customizations + # we made in the _cdf. + return self._cdf(-x, -a) + + def _isf(self, x, a): + return _boost._skewnorm_isf(x, 0, 1, a) + + def _rvs(self, a, size=None, random_state=None): + u0 = random_state.normal(size=size) + v = random_state.normal(size=size) + d = a/np.sqrt(1 + a**2) + u1 = d*u0 + v*np.sqrt(1 - d**2) + return np.where(u0 >= 0, u1, -u1) + + def _stats(self, a, moments='mvsk'): + output = [None, None, None, None] + const = np.sqrt(2/np.pi) * a/np.sqrt(1 + a**2) + + if 'm' in moments: + output[0] = const + if 'v' in moments: + output[1] = 1 - const**2 + if 's' in moments: + output[2] = ((4 - np.pi)/2) * (const/np.sqrt(1 - const**2))**3 + if 'k' in moments: + output[3] = (2*(np.pi - 3)) * (const**4/(1 - const**2)**2) + + return output + + # For odd order, the each noncentral moment of the skew-normal distribution + # with location 0 and scale 1 can be expressed as a polynomial in delta, + # where delta = a/sqrt(1 + a**2) and `a` is the skew-normal shape + # parameter. The dictionary _skewnorm_odd_moments defines those + # polynomials for orders up to 19. The dict is implemented as a cached + # property to reduce the impact of the creation of the dict on import time. + @cached_property + def _skewnorm_odd_moments(self): + skewnorm_odd_moments = { + 1: Polynomial([1]), + 3: Polynomial([3, -1]), + 5: Polynomial([15, -10, 3]), + 7: Polynomial([105, -105, 63, -15]), + 9: Polynomial([945, -1260, 1134, -540, 105]), + 11: Polynomial([10395, -17325, 20790, -14850, 5775, -945]), + 13: Polynomial([135135, -270270, 405405, -386100, 225225, -73710, + 10395]), + 15: Polynomial([2027025, -4729725, 8513505, -10135125, 7882875, + -3869775, 1091475, -135135]), + 17: Polynomial([34459425, -91891800, 192972780, -275675400, + 268017750, -175429800, 74220300, -18378360, + 2027025]), + 19: Polynomial([654729075, -1964187225, 4714049340, -7856748900, + 9166207050, -7499623950, 4230557100, -1571349780, + 346621275, -34459425]), + } + return skewnorm_odd_moments + + def _munp(self, order, a): + if order & 1: + if order > 19: + raise NotImplementedError("skewnorm noncentral moments not " + "implemented for odd orders greater " + "than 19.") + # Use the precomputed polynomials that were derived from the + # moment generating function. + delta = a/np.sqrt(1 + a**2) + return (delta * self._skewnorm_odd_moments[order](delta**2) + * _SQRT_2_OVER_PI) + else: + # For even order, the moment is just (order-1)!!, where !! is the + # notation for the double factorial; for an odd integer m, m!! is + # m*(m-2)*...*3*1. + # We could use special.factorial2, but we know the argument is odd, + # so avoid the overhead of that function and compute the result + # directly here. + return sc.gamma((order + 1)/2) * 2**(order/2) / _SQRT_PI + + @extend_notes_in_docstring(rv_continuous, notes="""\ + If ``method='mm'``, parameters fixed by the user are respected, and the + remaining parameters are used to match distribution and sample moments + where possible. For example, if the user fixes the location with + ``floc``, the parameters will only match the distribution skewness and + variance to the sample skewness and variance; no attempt will be made + to match the means or minimize a norm of the errors. + Note that the maximum possible skewness magnitude of a + `scipy.stats.skewnorm` distribution is approximately 0.9952717; if the + magnitude of the data's sample skewness exceeds this, the returned + shape parameter ``a`` will be infinite. + \n\n""") + def fit(self, data, *args, **kwds): + if kwds.pop("superfit", False): + return super().fit(data, *args, **kwds) + if isinstance(data, CensoredData): + if data.num_censored() == 0: + data = data._uncensor() + else: + return super().fit(data, *args, **kwds) + + # this extracts fixed shape, location, and scale however they + # are specified, and also leaves them in `kwds` + data, fa, floc, fscale = _check_fit_input_parameters(self, data, + args, kwds) + method = kwds.get("method", "mle").lower() + + # See https://en.wikipedia.org/wiki/Skew_normal_distribution for + # moment formulas. + def skew_d(d): # skewness in terms of delta + return (4-np.pi)/2 * ((d * np.sqrt(2 / np.pi))**3 + / (1 - 2*d**2 / np.pi)**(3/2)) + def d_skew(skew): # delta in terms of skewness + s_23 = np.abs(skew)**(2/3) + return np.sign(skew) * np.sqrt( + np.pi/2 * s_23 / (s_23 + ((4 - np.pi)/2)**(2/3)) + ) + + # If method is method of moments, we don't need the user's guesses. + # Otherwise, extract the guesses from args and kwds. + if method == "mm": + a, loc, scale = None, None, None + else: + a = args[0] if len(args) else None + loc = kwds.pop('loc', None) + scale = kwds.pop('scale', None) + + if fa is None and a is None: # not fixed and no guess: use MoM + # Solve for a that matches sample distribution skewness to sample + # skewness. + s = stats.skew(data) + if method == 'mle': + # For MLE initial conditions, clip skewness to a large but + # reasonable value in case the data skewness is out-of-range. + s = np.clip(s, -0.99, 0.99) + else: + s_max = skew_d(1) + s = np.clip(s, -s_max, s_max) + d = d_skew(s) + with np.errstate(divide='ignore'): + a = np.sqrt(np.divide(d**2, (1-d**2)))*np.sign(s) + else: + a = fa if fa is not None else a + d = a / np.sqrt(1 + a**2) + + if fscale is None and scale is None: + v = np.var(data) + scale = np.sqrt(v / (1 - 2*d**2/np.pi)) + elif fscale is not None: + scale = fscale + + if floc is None and loc is None: + m = np.mean(data) + loc = m - scale*d*np.sqrt(2/np.pi) + elif floc is not None: + loc = floc + + if method == 'mm': + return a, loc, scale + else: + # At this point, parameter "guesses" may equal the fixed parameters + # in kwds. No harm in passing them as guesses, too. + return super().fit(data, a, loc=loc, scale=scale, **kwds) + + +skewnorm = skewnorm_gen(name='skewnorm') + + +class trapezoid_gen(rv_continuous): + r"""A trapezoidal continuous random variable. + + %(before_notes)s + + Notes + ----- + The trapezoidal distribution can be represented with an up-sloping line + from ``loc`` to ``(loc + c*scale)``, then constant to ``(loc + d*scale)`` + and then downsloping from ``(loc + d*scale)`` to ``(loc+scale)``. This + defines the trapezoid base from ``loc`` to ``(loc+scale)`` and the flat + top from ``c`` to ``d`` proportional to the position along the base + with ``0 <= c <= d <= 1``. When ``c=d``, this is equivalent to `triang` + with the same values for `loc`, `scale` and `c`. + The method of [1]_ is used for computing moments. + + `trapezoid` takes :math:`c` and :math:`d` as shape parameters. + + %(after_notes)s + + The standard form is in the range [0, 1] with c the mode. + The location parameter shifts the start to `loc`. + The scale parameter changes the width from 1 to `scale`. + + %(example)s + + References + ---------- + .. [1] Kacker, R.N. and Lawrence, J.F. (2007). Trapezoidal and triangular + distributions for Type B evaluation of standard uncertainty. + Metrologia 44, 117-127. :doi:`10.1088/0026-1394/44/2/003` + + + """ + def _argcheck(self, c, d): + return (c >= 0) & (c <= 1) & (d >= 0) & (d <= 1) & (d >= c) + + def _shape_info(self): + ic = _ShapeInfo("c", False, (0, 1.0), (True, True)) + id = _ShapeInfo("d", False, (0, 1.0), (True, True)) + return [ic, id] + + def _pdf(self, x, c, d): + u = 2 / (d-c+1) + + return _lazyselect([x < c, + (c <= x) & (x <= d), + x > d], + [lambda x, c, d, u: u * x / c, + lambda x, c, d, u: u, + lambda x, c, d, u: u * (1-x) / (1-d)], + (x, c, d, u)) + + def _cdf(self, x, c, d): + return _lazyselect([x < c, + (c <= x) & (x <= d), + x > d], + [lambda x, c, d: x**2 / c / (d-c+1), + lambda x, c, d: (c + 2 * (x-c)) / (d-c+1), + lambda x, c, d: 1-((1-x) ** 2 + / (d-c+1) / (1-d))], + (x, c, d)) + + def _ppf(self, q, c, d): + qc, qd = self._cdf(c, c, d), self._cdf(d, c, d) + condlist = [q < qc, q <= qd, q > qd] + choicelist = [np.sqrt(q * c * (1 + d - c)), + 0.5 * q * (1 + d - c) + 0.5 * c, + 1 - np.sqrt((1 - q) * (d - c + 1) * (1 - d))] + return np.select(condlist, choicelist) + + def _munp(self, n, c, d): + # Using the parameterization from Kacker, 2007, with + # a=bottom left, c=top left, d=top right, b=bottom right, then + # E[X^n] = h/(n+1)/(n+2) [(b^{n+2}-d^{n+2})/(b-d) + # - ((c^{n+2} - a^{n+2})/(c-a)] + # with h = 2/((b-a) - (d-c)). The corresponding parameterization + # in scipy, has a'=loc, c'=loc+c*scale, d'=loc+d*scale, b'=loc+scale, + # which for standard form reduces to a'=0, b'=1, c'=c, d'=d. + # Substituting into E[X^n] gives the bd' term as (1 - d^{n+2})/(1 - d) + # and the ac' term as c^{n-1} for the standard form. The bd' term has + # numerical difficulties near d=1, so replace (1 - d^{n+2})/(1-d) + # with expm1((n+2)*log(d))/(d-1). + # Testing with n=18 for c=(1e-30,1-eps) shows that this is stable. + # We still require an explicit test for d=1 to prevent divide by zero, + # and now a test for d=0 to prevent log(0). + ab_term = c**(n+1) + dc_term = _lazyselect( + [d == 0.0, (0.0 < d) & (d < 1.0), d == 1.0], + [lambda d: 1.0, + lambda d: np.expm1((n+2) * np.log(d)) / (d-1.0), + lambda d: n+2], + [d]) + val = 2.0 / (1.0+d-c) * (dc_term - ab_term) / ((n+1) * (n+2)) + return val + + def _entropy(self, c, d): + # Using the parameterization from Wikipedia (van Dorp, 2003) + # with a=bottom left, c=top left, d=top right, b=bottom right + # gives a'=loc, b'=loc+c*scale, c'=loc+d*scale, d'=loc+scale, + # which for loc=0, scale=1 is a'=0, b'=c, c'=d, d'=1. + # Substituting into the entropy formula from Wikipedia gives + # the following result. + return 0.5 * (1.0-d+c) / (1.0+d-c) + np.log(0.5 * (1.0+d-c)) + + +trapezoid = trapezoid_gen(a=0.0, b=1.0, name="trapezoid") +# Note: alias kept for backwards compatibility. Rename was done +# because trapz is a slur in colloquial English (see gh-12924). +trapz = trapezoid_gen(a=0.0, b=1.0, name="trapz") +if trapz.__doc__: + trapz.__doc__ = "trapz is an alias for `trapezoid`" + + +class triang_gen(rv_continuous): + r"""A triangular continuous random variable. + + %(before_notes)s + + Notes + ----- + The triangular distribution can be represented with an up-sloping line from + ``loc`` to ``(loc + c*scale)`` and then downsloping for ``(loc + c*scale)`` + to ``(loc + scale)``. + + `triang` takes ``c`` as a shape parameter for :math:`0 \le c \le 1`. + + %(after_notes)s + + The standard form is in the range [0, 1] with c the mode. + The location parameter shifts the start to `loc`. + The scale parameter changes the width from 1 to `scale`. + + %(example)s + + """ + def _rvs(self, c, size=None, random_state=None): + return random_state.triangular(0, c, 1, size) + + def _argcheck(self, c): + return (c >= 0) & (c <= 1) + + def _shape_info(self): + return [_ShapeInfo("c", False, (0, 1.0), (True, True))] + + def _pdf(self, x, c): + # 0: edge case where c=0 + # 1: generalised case for x < c, don't use x <= c, as it doesn't cope + # with c = 0. + # 2: generalised case for x >= c, but doesn't cope with c = 1 + # 3: edge case where c=1 + r = _lazyselect([c == 0, + x < c, + (x >= c) & (c != 1), + c == 1], + [lambda x, c: 2 - 2 * x, + lambda x, c: 2 * x / c, + lambda x, c: 2 * (1 - x) / (1 - c), + lambda x, c: 2 * x], + (x, c)) + return r + + def _cdf(self, x, c): + r = _lazyselect([c == 0, + x < c, + (x >= c) & (c != 1), + c == 1], + [lambda x, c: 2*x - x*x, + lambda x, c: x * x / c, + lambda x, c: (x*x - 2*x + c) / (c-1), + lambda x, c: x * x], + (x, c)) + return r + + def _ppf(self, q, c): + return np.where(q < c, np.sqrt(c * q), 1-np.sqrt((1-c) * (1-q))) + + def _stats(self, c): + return ((c+1.0)/3.0, + (1.0-c+c*c)/18, + np.sqrt(2)*(2*c-1)*(c+1)*(c-2) / (5*np.power((1.0-c+c*c), 1.5)), + -3.0/5.0) + + def _entropy(self, c): + return 0.5-np.log(2) + + +triang = triang_gen(a=0.0, b=1.0, name="triang") + + +class truncexpon_gen(rv_continuous): + r"""A truncated exponential continuous random variable. + + %(before_notes)s + + Notes + ----- + The probability density function for `truncexpon` is: + + .. math:: + + f(x, b) = \frac{\exp(-x)}{1 - \exp(-b)} + + for :math:`0 <= x <= b`. + + `truncexpon` takes ``b`` as a shape parameter for :math:`b`. + + %(after_notes)s + + %(example)s + + """ + def _shape_info(self): + return [_ShapeInfo("b", False, (0, np.inf), (False, False))] + + def _get_support(self, b): + return self.a, b + + def _pdf(self, x, b): + # truncexpon.pdf(x, b) = exp(-x) / (1-exp(-b)) + return np.exp(-x)/(-sc.expm1(-b)) + + def _logpdf(self, x, b): + return -x - np.log(-sc.expm1(-b)) + + def _cdf(self, x, b): + return sc.expm1(-x)/sc.expm1(-b) + + def _ppf(self, q, b): + return -sc.log1p(q*sc.expm1(-b)) + + def _sf(self, x, b): + return (np.exp(-b) - np.exp(-x))/sc.expm1(-b) + + def _isf(self, q, b): + return -np.log(np.exp(-b) - q * sc.expm1(-b)) + + def _munp(self, n, b): + # wrong answer with formula, same as in continuous.pdf + # return sc.gamman+1)-sc.gammainc1+n, b) + if n == 1: + return (1-(b+1)*np.exp(-b))/(-sc.expm1(-b)) + elif n == 2: + return 2*(1-0.5*(b*b+2*b+2)*np.exp(-b))/(-sc.expm1(-b)) + else: + # return generic for higher moments + return super()._munp(n, b) + + def _entropy(self, b): + eB = np.exp(b) + return np.log(eB-1)+(1+eB*(b-1.0))/(1.0-eB) + + +truncexpon = truncexpon_gen(a=0.0, name='truncexpon') + + +# logsumexp trick for log(p + q) with only log(p) and log(q) +def _log_sum(log_p, log_q): + return sc.logsumexp([log_p, log_q], axis=0) + + +# same as above, but using -exp(x) = exp(x + πi) +def _log_diff(log_p, log_q): + return sc.logsumexp([log_p, log_q+np.pi*1j], axis=0) + + +def _log_gauss_mass(a, b): + """Log of Gaussian probability mass within an interval""" + a, b = np.broadcast_arrays(a, b) + + # Calculations in right tail are inaccurate, so we'll exploit the + # symmetry and work only in the left tail + case_left = b <= 0 + case_right = a > 0 + case_central = ~(case_left | case_right) + + def mass_case_left(a, b): + return _log_diff(_norm_logcdf(b), _norm_logcdf(a)) + + def mass_case_right(a, b): + return mass_case_left(-b, -a) + + def mass_case_central(a, b): + # Previously, this was implemented as: + # left_mass = mass_case_left(a, 0) + # right_mass = mass_case_right(0, b) + # return _log_sum(left_mass, right_mass) + # Catastrophic cancellation occurs as np.exp(log_mass) approaches 1. + # Correct for this with an alternative formulation. + # We're not concerned with underflow here: if only one term + # underflows, it was insignificant; if both terms underflow, + # the result can't accurately be represented in logspace anyway + # because sc.log1p(x) ~ x for small x. + return sc.log1p(-_norm_cdf(a) - _norm_cdf(-b)) + + # _lazyselect not working; don't care to debug it + out = np.full_like(a, fill_value=np.nan, dtype=np.complex128) + if a[case_left].size: + out[case_left] = mass_case_left(a[case_left], b[case_left]) + if a[case_right].size: + out[case_right] = mass_case_right(a[case_right], b[case_right]) + if a[case_central].size: + out[case_central] = mass_case_central(a[case_central], b[case_central]) + return np.real(out) # discard ~0j + + +class truncnorm_gen(rv_continuous): + r"""A truncated normal continuous random variable. + + %(before_notes)s + + Notes + ----- + This distribution is the normal distribution centered on ``loc`` (default + 0), with standard deviation ``scale`` (default 1), and truncated at ``a`` + and ``b`` *standard deviations* from ``loc``. For arbitrary ``loc`` and + ``scale``, ``a`` and ``b`` are *not* the abscissae at which the shifted + and scaled distribution is truncated. + + .. note:: + If ``a_trunc`` and ``b_trunc`` are the abscissae at which we wish + to truncate the distribution (as opposed to the number of standard + deviations from ``loc``), then we can calculate the distribution + parameters ``a`` and ``b`` as follows:: + + a, b = (a_trunc - loc) / scale, (b_trunc - loc) / scale + + This is a common point of confusion. For additional clarification, + please see the example below. + + %(example)s + + In the examples above, ``loc=0`` and ``scale=1``, so the plot is truncated + at ``a`` on the left and ``b`` on the right. However, suppose we were to + produce the same histogram with ``loc = 1`` and ``scale=0.5``. + + >>> loc, scale = 1, 0.5 + >>> rv = truncnorm(a, b, loc=loc, scale=scale) + >>> x = np.linspace(truncnorm.ppf(0.01, a, b), + ... truncnorm.ppf(0.99, a, b), 100) + >>> r = rv.rvs(size=1000) + + >>> fig, ax = plt.subplots(1, 1) + >>> ax.plot(x, rv.pdf(x), 'k-', lw=2, label='frozen pdf') + >>> ax.hist(r, density=True, bins='auto', histtype='stepfilled', alpha=0.2) + >>> ax.set_xlim(a, b) + >>> ax.legend(loc='best', frameon=False) + >>> plt.show() + + Note that the distribution is no longer appears to be truncated at + abscissae ``a`` and ``b``. That is because the *standard* normal + distribution is first truncated at ``a`` and ``b``, *then* the resulting + distribution is scaled by ``scale`` and shifted by ``loc``. If we instead + want the shifted and scaled distribution to be truncated at ``a`` and + ``b``, we need to transform these values before passing them as the + distribution parameters. + + >>> a_transformed, b_transformed = (a - loc) / scale, (b - loc) / scale + >>> rv = truncnorm(a_transformed, b_transformed, loc=loc, scale=scale) + >>> x = np.linspace(truncnorm.ppf(0.01, a, b), + ... truncnorm.ppf(0.99, a, b), 100) + >>> r = rv.rvs(size=10000) + + >>> fig, ax = plt.subplots(1, 1) + >>> ax.plot(x, rv.pdf(x), 'k-', lw=2, label='frozen pdf') + >>> ax.hist(r, density=True, bins='auto', histtype='stepfilled', alpha=0.2) + >>> ax.set_xlim(a-0.1, b+0.1) + >>> ax.legend(loc='best', frameon=False) + >>> plt.show() + """ + + def _argcheck(self, a, b): + return a < b + + def _shape_info(self): + ia = _ShapeInfo("a", False, (-np.inf, np.inf), (True, False)) + ib = _ShapeInfo("b", False, (-np.inf, np.inf), (False, True)) + return [ia, ib] + + def _fitstart(self, data): + # Reasonable, since support is [a, b] + if isinstance(data, CensoredData): + data = data._uncensor() + return super()._fitstart(data, args=(np.min(data), np.max(data))) + + def _get_support(self, a, b): + return a, b + + def _pdf(self, x, a, b): + return np.exp(self._logpdf(x, a, b)) + + def _logpdf(self, x, a, b): + return _norm_logpdf(x) - _log_gauss_mass(a, b) + + def _cdf(self, x, a, b): + return np.exp(self._logcdf(x, a, b)) + + def _logcdf(self, x, a, b): + x, a, b = np.broadcast_arrays(x, a, b) + logcdf = np.asarray(_log_gauss_mass(a, x) - _log_gauss_mass(a, b)) + i = logcdf > -0.1 # avoid catastrophic cancellation + if np.any(i): + logcdf[i] = np.log1p(-np.exp(self._logsf(x[i], a[i], b[i]))) + return logcdf + + def _sf(self, x, a, b): + return np.exp(self._logsf(x, a, b)) + + def _logsf(self, x, a, b): + x, a, b = np.broadcast_arrays(x, a, b) + logsf = np.asarray(_log_gauss_mass(x, b) - _log_gauss_mass(a, b)) + i = logsf > -0.1 # avoid catastrophic cancellation + if np.any(i): + logsf[i] = np.log1p(-np.exp(self._logcdf(x[i], a[i], b[i]))) + return logsf + + def _entropy(self, a, b): + A = _norm_cdf(a) + B = _norm_cdf(b) + Z = B - A + C = np.log(np.sqrt(2 * np.pi * np.e) * Z) + D = (a * _norm_pdf(a) - b * _norm_pdf(b)) / (2 * Z) + h = C + D + return h + + def _ppf(self, q, a, b): + q, a, b = np.broadcast_arrays(q, a, b) + + case_left = a < 0 + case_right = ~case_left + + def ppf_left(q, a, b): + log_Phi_x = _log_sum(_norm_logcdf(a), + np.log(q) + _log_gauss_mass(a, b)) + return sc.ndtri_exp(log_Phi_x) + + def ppf_right(q, a, b): + log_Phi_x = _log_sum(_norm_logcdf(-b), + np.log1p(-q) + _log_gauss_mass(a, b)) + return -sc.ndtri_exp(log_Phi_x) + + out = np.empty_like(q) + + q_left = q[case_left] + q_right = q[case_right] + + if q_left.size: + out[case_left] = ppf_left(q_left, a[case_left], b[case_left]) + if q_right.size: + out[case_right] = ppf_right(q_right, a[case_right], b[case_right]) + + return out + + def _isf(self, q, a, b): + # Mostly copy-paste of _ppf, but I think this is simpler than combining + q, a, b = np.broadcast_arrays(q, a, b) + + case_left = b < 0 + case_right = ~case_left + + def isf_left(q, a, b): + log_Phi_x = _log_diff(_norm_logcdf(b), + np.log(q) + _log_gauss_mass(a, b)) + return sc.ndtri_exp(np.real(log_Phi_x)) + + def isf_right(q, a, b): + log_Phi_x = _log_diff(_norm_logcdf(-a), + np.log1p(-q) + _log_gauss_mass(a, b)) + return -sc.ndtri_exp(np.real(log_Phi_x)) + + out = np.empty_like(q) + + q_left = q[case_left] + q_right = q[case_right] + + if q_left.size: + out[case_left] = isf_left(q_left, a[case_left], b[case_left]) + if q_right.size: + out[case_right] = isf_right(q_right, a[case_right], b[case_right]) + + return out + + def _munp(self, n, a, b): + def n_th_moment(n, a, b): + """ + Returns n-th moment. Defined only if n >= 0. + Function cannot broadcast due to the loop over n + """ + pA, pB = self._pdf(np.asarray([a, b]), a, b) + probs = [pA, -pB] + moments = [0, 1] + for k in range(1, n+1): + # a or b might be infinite, and the corresponding pdf value + # is 0 in that case, but nan is returned for the + # multiplication. However, as b->infinity, pdf(b)*b**k -> 0. + # So it is safe to use _lazywhere to avoid the nan. + vals = _lazywhere(probs, [probs, [a, b]], + lambda x, y: x * y**(k-1), fillvalue=0) + mk = np.sum(vals) + (k-1) * moments[-2] + moments.append(mk) + return moments[-1] + + return _lazywhere((n >= 0) & (a == a) & (b == b), (n, a, b), + np.vectorize(n_th_moment, otypes=[np.float64]), + np.nan) + + def _stats(self, a, b, moments='mv'): + pA, pB = self.pdf(np.array([a, b]), a, b) + + def _truncnorm_stats_scalar(a, b, pA, pB, moments): + m1 = pA - pB + mu = m1 + # use _lazywhere to avoid nan (See detailed comment in _munp) + probs = [pA, -pB] + vals = _lazywhere(probs, [probs, [a, b]], lambda x, y: x*y, + fillvalue=0) + m2 = 1 + np.sum(vals) + vals = _lazywhere(probs, [probs, [a-mu, b-mu]], lambda x, y: x*y, + fillvalue=0) + # mu2 = m2 - mu**2, but not as numerically stable as: + # mu2 = (a-mu)*pA - (b-mu)*pB + 1 + mu2 = 1 + np.sum(vals) + vals = _lazywhere(probs, [probs, [a, b]], lambda x, y: x*y**2, + fillvalue=0) + m3 = 2*m1 + np.sum(vals) + vals = _lazywhere(probs, [probs, [a, b]], lambda x, y: x*y**3, + fillvalue=0) + m4 = 3*m2 + np.sum(vals) + + mu3 = m3 + m1 * (-3*m2 + 2*m1**2) + g1 = mu3 / np.power(mu2, 1.5) + mu4 = m4 + m1*(-4*m3 + 3*m1*(2*m2 - m1**2)) + g2 = mu4 / mu2**2 - 3 + return mu, mu2, g1, g2 + + _truncnorm_stats = np.vectorize(_truncnorm_stats_scalar, + excluded=('moments',)) + return _truncnorm_stats(a, b, pA, pB, moments) + + +truncnorm = truncnorm_gen(name='truncnorm', momtype=1) + + +class truncpareto_gen(rv_continuous): + r"""An upper truncated Pareto continuous random variable. + + %(before_notes)s + + See Also + -------- + pareto : Pareto distribution + + Notes + ----- + The probability density function for `truncpareto` is: + + .. math:: + + f(x, b, c) = \frac{b}{1 - c^{-b}} \frac{1}{x^{b+1}} + + for :math:`b > 0`, :math:`c > 1` and :math:`1 \le x \le c`. + + `truncpareto` takes `b` and `c` as shape parameters for :math:`b` and + :math:`c`. + + Notice that the upper truncation value :math:`c` is defined in + standardized form so that random values of an unscaled, unshifted variable + are within the range ``[1, c]``. + If ``u_r`` is the upper bound to a scaled and/or shifted variable, + then ``c = (u_r - loc) / scale``. In other words, the support of the + distribution becomes ``(scale + loc) <= x <= (c*scale + loc)`` when + `scale` and/or `loc` are provided. + + %(after_notes)s + + References + ---------- + .. [1] Burroughs, S. M., and Tebbens S. F. + "Upper-truncated power laws in natural systems." + Pure and Applied Geophysics 158.4 (2001): 741-757. + + %(example)s + + """ + + def _shape_info(self): + ib = _ShapeInfo("b", False, (0.0, np.inf), (False, False)) + ic = _ShapeInfo("c", False, (1.0, np.inf), (False, False)) + return [ib, ic] + + def _argcheck(self, b, c): + return (b > 0.) & (c > 1.) + + def _get_support(self, b, c): + return self.a, c + + def _pdf(self, x, b, c): + return b * x**-(b+1) / (1 - 1/c**b) + + def _logpdf(self, x, b, c): + return np.log(b) - np.log(-np.expm1(-b*np.log(c))) - (b+1)*np.log(x) + + def _cdf(self, x, b, c): + return (1 - x**-b) / (1 - 1/c**b) + + def _logcdf(self, x, b, c): + return np.log1p(-x**-b) - np.log1p(-1/c**b) + + def _ppf(self, q, b, c): + return pow(1 - (1 - 1/c**b)*q, -1/b) + + def _sf(self, x, b, c): + return (x**-b - 1/c**b) / (1 - 1/c**b) + + def _logsf(self, x, b, c): + return np.log(x**-b - 1/c**b) - np.log1p(-1/c**b) + + def _isf(self, q, b, c): + return pow(1/c**b + (1 - 1/c**b)*q, -1/b) + + def _entropy(self, b, c): + return -(np.log(b/(1 - 1/c**b)) + + (b+1)*(np.log(c)/(c**b - 1) - 1/b)) + + def _munp(self, n, b, c): + if (n == b).all(): + return b*np.log(c) / (1 - 1/c**b) + else: + return b / (b-n) * (c**b - c**n) / (c**b - 1) + + def _fitstart(self, data): + if isinstance(data, CensoredData): + data = data._uncensor() + b, loc, scale = pareto.fit(data) + c = (max(data) - loc)/scale + return b, c, loc, scale + + @_call_super_mom + @inherit_docstring_from(rv_continuous) + def fit(self, data, *args, **kwds): + if kwds.pop("superfit", False): + return super().fit(data, *args, **kwds) + + def log_mean(x): + return np.mean(np.log(x)) + + def harm_mean(x): + return 1/np.mean(1/x) + + def get_b(c, loc, scale): + u = (data-loc)/scale + harm_m = harm_mean(u) + log_m = log_mean(u) + quot = (harm_m-1)/log_m + return (1 - (quot-1) / (quot - (1 - 1/c)*harm_m/np.log(c)))/log_m + + def get_c(loc, scale): + return (mx - loc)/scale + + def get_loc(fc, fscale): + if fscale: # (fscale and fc) or (fscale and not fc) + loc = mn - fscale + return loc + if fc: + loc = (fc*mn - mx)/(fc - 1) + return loc + + def get_scale(loc): + return mn - loc + + # Functions used for optimisation; partial derivatives of + # the Lagrangian, set to equal 0. + + def dL_dLoc(loc, b_=None): + # Partial derivative wrt location. + # Optimised upon when no parameters, or only b, are fixed. + scale = get_scale(loc) + c = get_c(loc, scale) + b = get_b(c, loc, scale) if b_ is None else b_ + harm_m = harm_mean((data - loc)/scale) + return 1 - (1 + (c - 1)/(c**(b+1) - c)) * (1 - 1/(b+1)) * harm_m + + def dL_dB(b, logc, logm): + # Partial derivative wrt b. + # Optimised upon whenever at least one parameter but b is fixed, + # and b is free. + return b - np.log1p(b*logc / (1 - b*logm)) / logc + + def fallback(data, *args, **kwargs): + # Should any issue arise, default to the general fit method. + return super(truncpareto_gen, self).fit(data, *args, **kwargs) + + parameters = _check_fit_input_parameters(self, data, args, kwds) + data, fb, fc, floc, fscale = parameters + mn, mx = data.min(), data.max() + mn_inf = np.nextafter(mn, -np.inf) + + if (fb is not None + and fc is not None + and floc is not None + and fscale is not None): + raise ValueError("All parameters fixed." + "There is nothing to optimize.") + elif fc is None and floc is None and fscale is None: + if fb is None: + def cond_b(loc): + # b is positive only if this function is positive + scale = get_scale(loc) + c = get_c(loc, scale) + harm_m = harm_mean((data - loc)/scale) + return (1 + 1/(c-1)) * np.log(c) / harm_m - 1 + + # This gives an upper bound on loc allowing for a positive b. + # Iteratively look for a bracket for root_scalar. + mn_inf = np.nextafter(mn, -np.inf) + rbrack = mn_inf + i = 0 + lbrack = rbrack - 1 + while ((lbrack > -np.inf) + and (cond_b(lbrack)*cond_b(rbrack) >= 0)): + i += 1 + lbrack = rbrack - np.power(2., i) + if not lbrack > -np.inf: + return fallback(data, *args, **kwds) + res = root_scalar(cond_b, bracket=(lbrack, rbrack)) + if not res.converged: + return fallback(data, *args, **kwds) + + # Determine the MLE for loc. + # Iteratively look for a bracket for root_scalar. + rbrack = res.root - 1e-3 # grad_loc is numerically ill-behaved + lbrack = rbrack - 1 + i = 0 + while ((lbrack > -np.inf) + and (dL_dLoc(lbrack)*dL_dLoc(rbrack) >= 0)): + i += 1 + lbrack = rbrack - np.power(2., i) + if not lbrack > -np.inf: + return fallback(data, *args, **kwds) + res = root_scalar(dL_dLoc, bracket=(lbrack, rbrack)) + if not res.converged: + return fallback(data, *args, **kwds) + loc = res.root + scale = get_scale(loc) + c = get_c(loc, scale) + b = get_b(c, loc, scale) + + std_data = (data - loc)/scale + # The expression of b relies on b being bounded above. + up_bound_b = min(1/log_mean(std_data), + 1/(harm_mean(std_data)-1)) + if not (b < up_bound_b): + return fallback(data, *args, **kwds) + else: + # We know b is positive (or a FitError will be triggered) + # so we let loc get close to min(data). + rbrack = mn_inf + lbrack = mn_inf - 1 + i = 0 + # Iteratively look for a bracket for root_scalar. + while (lbrack > -np.inf + and (dL_dLoc(lbrack, fb) + * dL_dLoc(rbrack, fb) >= 0)): + i += 1 + lbrack = rbrack - 2**i + if not lbrack > -np.inf: + return fallback(data, *args, **kwds) + res = root_scalar(dL_dLoc, (fb,), + bracket=(lbrack, rbrack)) + if not res.converged: + return fallback(data, *args, **kwds) + loc = res.root + scale = get_scale(loc) + c = get_c(loc, scale) + b = fb + else: + # At least one of the parameters determining the support is fixed; + # the others then have analytical expressions from the constraints. + # The completely determined case (fixed c, loc and scale) + # has to be checked for not overflowing the support. + # If not fixed, b has to be determined numerically. + loc = floc if floc is not None else get_loc(fc, fscale) + scale = fscale or get_scale(loc) + c = fc or get_c(loc, scale) + + # Unscaled, translated values should be positive when the location + # is fixed. If it is not the case, we end up with negative `scale` + # and `c`, which would trigger a FitError before exiting the + # method. + if floc is not None and data.min() - floc < 0: + raise FitDataError("truncpareto", lower=1, upper=c) + + # Standardised values should be within the distribution support + # when all parameters controlling it are fixed. If it not the case, + # `fc` is overridden by `c` determined from `floc` and `fscale` when + # raising the exception. + if fc and (floc is not None) and fscale: + if data.max() > fc*fscale + floc: + raise FitDataError("truncpareto", lower=1, + upper=get_c(loc, scale)) + + # The other constraints should be automatically satisfied + # from the analytical expressions of the parameters. + # If fc or fscale are respectively less than one or less than 0, + # a FitError is triggered before exiting the method. + + if fb is None: + std_data = (data - loc)/scale + logm = log_mean(std_data) + logc = np.log(c) + # Condition for a positive root to exist. + if not (2*logm < logc): + return fallback(data, *args, **kwds) + + lbrack = 1/logm + 1/(logm - logc) + rbrack = np.nextafter(1/logm, 0) + try: + res = root_scalar(dL_dB, (logc, logm), + bracket=(lbrack, rbrack)) + # we should then never get there + if not res.converged: + return fallback(data, *args, **kwds) + b = res.root + except ValueError: + b = rbrack + else: + b = fb + + # The distribution requires that `scale+loc <= data <= c*scale+loc`. + # To avoid numerical issues, some tuning may be necessary. + # We adjust `scale` to satisfy the lower bound, and we adjust + # `c` to satisfy the upper bound. + if not (scale+loc) < mn: + if fscale: + loc = np.nextafter(loc, -np.inf) + else: + scale = get_scale(loc) + scale = np.nextafter(scale, 0) + if not (c*scale+loc) > mx: + c = get_c(loc, scale) + c = np.nextafter(c, np.inf) + + if not (np.all(self._argcheck(b, c)) and (scale > 0)): + return fallback(data, *args, **kwds) + + params_override = b, c, loc, scale + if floc is None and fscale is None: + # Based on testing in gh-16782, the following methods are only + # reliable if either `floc` or `fscale` are provided. They are + # fast, though, so might as well see if they are better than the + # generic method. + params_super = fallback(data, *args, **kwds) + nllf_override = self.nnlf(params_override, data) + nllf_super = self.nnlf(params_super, data) + if nllf_super < nllf_override: + return params_super + + return params_override + + +truncpareto = truncpareto_gen(a=1.0, name='truncpareto') + + +class tukeylambda_gen(rv_continuous): + r"""A Tukey-Lamdba continuous random variable. + + %(before_notes)s + + Notes + ----- + A flexible distribution, able to represent and interpolate between the + following distributions: + + - Cauchy (:math:`lambda = -1`) + - logistic (:math:`lambda = 0`) + - approx Normal (:math:`lambda = 0.14`) + - uniform from -1 to 1 (:math:`lambda = 1`) + + `tukeylambda` takes a real number :math:`lambda` (denoted ``lam`` + in the implementation) as a shape parameter. + + %(after_notes)s + + %(example)s + + """ + def _argcheck(self, lam): + return np.isfinite(lam) + + def _shape_info(self): + return [_ShapeInfo("lam", False, (-np.inf, np.inf), (False, False))] + + def _pdf(self, x, lam): + Fx = np.asarray(sc.tklmbda(x, lam)) + Px = Fx**(lam-1.0) + (np.asarray(1-Fx))**(lam-1.0) + Px = 1.0/np.asarray(Px) + return np.where((lam <= 0) | (abs(x) < 1.0/np.asarray(lam)), Px, 0.0) + + def _cdf(self, x, lam): + return sc.tklmbda(x, lam) + + def _ppf(self, q, lam): + return sc.boxcox(q, lam) - sc.boxcox1p(-q, lam) + + def _stats(self, lam): + return 0, _tlvar(lam), 0, _tlkurt(lam) + + def _entropy(self, lam): + def integ(p): + return np.log(pow(p, lam-1)+pow(1-p, lam-1)) + return integrate.quad(integ, 0, 1)[0] + + +tukeylambda = tukeylambda_gen(name='tukeylambda') + + +class FitUniformFixedScaleDataError(FitDataError): + def __init__(self, ptp, fscale): + self.args = ( + "Invalid values in `data`. Maximum likelihood estimation with " + "the uniform distribution and fixed scale requires that " + f"np.ptp(data) <= fscale, but np.ptp(data) = {ptp} and " + f"fscale = {fscale}." + ) + + +class uniform_gen(rv_continuous): + r"""A uniform continuous random variable. + + In the standard form, the distribution is uniform on ``[0, 1]``. Using + the parameters ``loc`` and ``scale``, one obtains the uniform distribution + on ``[loc, loc + scale]``. + + %(before_notes)s + + %(example)s + + """ + def _shape_info(self): + return [] + + def _rvs(self, size=None, random_state=None): + return random_state.uniform(0.0, 1.0, size) + + def _pdf(self, x): + return 1.0*(x == x) + + def _cdf(self, x): + return x + + def _ppf(self, q): + return q + + def _stats(self): + return 0.5, 1.0/12, 0, -1.2 + + def _entropy(self): + return 0.0 + + @_call_super_mom + def fit(self, data, *args, **kwds): + """ + Maximum likelihood estimate for the location and scale parameters. + + `uniform.fit` uses only the following parameters. Because exact + formulas are used, the parameters related to optimization that are + available in the `fit` method of other distributions are ignored + here. The only positional argument accepted is `data`. + + Parameters + ---------- + data : array_like + Data to use in calculating the maximum likelihood estimate. + floc : float, optional + Hold the location parameter fixed to the specified value. + fscale : float, optional + Hold the scale parameter fixed to the specified value. + + Returns + ------- + loc, scale : float + Maximum likelihood estimates for the location and scale. + + Notes + ----- + An error is raised if `floc` is given and any values in `data` are + less than `floc`, or if `fscale` is given and `fscale` is less + than ``data.max() - data.min()``. An error is also raised if both + `floc` and `fscale` are given. + + Examples + -------- + >>> import numpy as np + >>> from scipy.stats import uniform + + We'll fit the uniform distribution to `x`: + + >>> x = np.array([2, 2.5, 3.1, 9.5, 13.0]) + + For a uniform distribution MLE, the location is the minimum of the + data, and the scale is the maximum minus the minimum. + + >>> loc, scale = uniform.fit(x) + >>> loc + 2.0 + >>> scale + 11.0 + + If we know the data comes from a uniform distribution where the support + starts at 0, we can use `floc=0`: + + >>> loc, scale = uniform.fit(x, floc=0) + >>> loc + 0.0 + >>> scale + 13.0 + + Alternatively, if we know the length of the support is 12, we can use + `fscale=12`: + + >>> loc, scale = uniform.fit(x, fscale=12) + >>> loc + 1.5 + >>> scale + 12.0 + + In that last example, the support interval is [1.5, 13.5]. This + solution is not unique. For example, the distribution with ``loc=2`` + and ``scale=12`` has the same likelihood as the one above. When + `fscale` is given and it is larger than ``data.max() - data.min()``, + the parameters returned by the `fit` method center the support over + the interval ``[data.min(), data.max()]``. + + """ + if len(args) > 0: + raise TypeError("Too many arguments.") + + floc = kwds.pop('floc', None) + fscale = kwds.pop('fscale', None) + + _remove_optimizer_parameters(kwds) + + if floc is not None and fscale is not None: + # This check is for consistency with `rv_continuous.fit`. + raise ValueError("All parameters fixed. There is nothing to " + "optimize.") + + data = np.asarray(data) + + if not np.isfinite(data).all(): + raise ValueError("The data contains non-finite values.") + + # MLE for the uniform distribution + # -------------------------------- + # The PDF is + # + # f(x, loc, scale) = {1/scale for loc <= x <= loc + scale + # {0 otherwise} + # + # The likelihood function is + # L(x, loc, scale) = (1/scale)**n + # where n is len(x), assuming loc <= x <= loc + scale for all x. + # The log-likelihood is + # l(x, loc, scale) = -n*log(scale) + # The log-likelihood is maximized by making scale as small as possible, + # while keeping loc <= x <= loc + scale. So if neither loc nor scale + # are fixed, the log-likelihood is maximized by choosing + # loc = x.min() + # scale = np.ptp(x) + # If loc is fixed, it must be less than or equal to x.min(), and then + # the scale is + # scale = x.max() - loc + # If scale is fixed, it must not be less than np.ptp(x). If scale is + # greater than np.ptp(x), the solution is not unique. Note that the + # likelihood does not depend on loc, except for the requirement that + # loc <= x <= loc + scale. All choices of loc for which + # x.max() - scale <= loc <= x.min() + # have the same log-likelihood. In this case, we choose loc such that + # the support is centered over the interval [data.min(), data.max()]: + # loc = x.min() = 0.5*(scale - np.ptp(x)) + + if fscale is None: + # scale is not fixed. + if floc is None: + # loc is not fixed, scale is not fixed. + loc = data.min() + scale = np.ptp(data) + else: + # loc is fixed, scale is not fixed. + loc = floc + scale = data.max() - loc + if data.min() < loc: + raise FitDataError("uniform", lower=loc, upper=loc + scale) + else: + # loc is not fixed, scale is fixed. + ptp = np.ptp(data) + if ptp > fscale: + raise FitUniformFixedScaleDataError(ptp=ptp, fscale=fscale) + # If ptp < fscale, the ML estimate is not unique; see the comments + # above. We choose the distribution for which the support is + # centered over the interval [data.min(), data.max()]. + loc = data.min() - 0.5*(fscale - ptp) + scale = fscale + + # We expect the return values to be floating point, so ensure it + # by explicitly converting to float. + return float(loc), float(scale) + + +uniform = uniform_gen(a=0.0, b=1.0, name='uniform') + + +class vonmises_gen(rv_continuous): + r"""A Von Mises continuous random variable. + + %(before_notes)s + + See Also + -------- + scipy.stats.vonmises_fisher : Von-Mises Fisher distribution on a + hypersphere + + Notes + ----- + The probability density function for `vonmises` and `vonmises_line` is: + + .. math:: + + f(x, \kappa) = \frac{ \exp(\kappa \cos(x)) }{ 2 \pi I_0(\kappa) } + + for :math:`-\pi \le x \le \pi`, :math:`\kappa \ge 0`. :math:`I_0` is the + modified Bessel function of order zero (`scipy.special.i0`). + + `vonmises` is a circular distribution which does not restrict the + distribution to a fixed interval. Currently, there is no circular + distribution framework in SciPy. The ``cdf`` is implemented such that + ``cdf(x + 2*np.pi) == cdf(x) + 1``. + + `vonmises_line` is the same distribution, defined on :math:`[-\pi, \pi]` + on the real line. This is a regular (i.e. non-circular) distribution. + + Note about distribution parameters: `vonmises` and `vonmises_line` take + ``kappa`` as a shape parameter (concentration) and ``loc`` as the location + (circular mean). A ``scale`` parameter is accepted but does not have any + effect. + + Examples + -------- + Import the necessary modules. + + >>> import numpy as np + >>> import matplotlib.pyplot as plt + >>> from scipy.stats import vonmises + + Define distribution parameters. + + >>> loc = 0.5 * np.pi # circular mean + >>> kappa = 1 # concentration + + Compute the probability density at ``x=0`` via the ``pdf`` method. + + >>> vonmises.pdf(0, loc=loc, kappa=kappa) + 0.12570826359722018 + + Verify that the percentile function ``ppf`` inverts the cumulative + distribution function ``cdf`` up to floating point accuracy. + + >>> x = 1 + >>> cdf_value = vonmises.cdf(x, loc=loc, kappa=kappa) + >>> ppf_value = vonmises.ppf(cdf_value, loc=loc, kappa=kappa) + >>> x, cdf_value, ppf_value + (1, 0.31489339900904967, 1.0000000000000004) + + Draw 1000 random variates by calling the ``rvs`` method. + + >>> sample_size = 1000 + >>> sample = vonmises(loc=loc, kappa=kappa).rvs(sample_size) + + Plot the von Mises density on a Cartesian and polar grid to emphasize + that it is a circular distribution. + + >>> fig = plt.figure(figsize=(12, 6)) + >>> left = plt.subplot(121) + >>> right = plt.subplot(122, projection='polar') + >>> x = np.linspace(-np.pi, np.pi, 500) + >>> vonmises_pdf = vonmises.pdf(x, loc=loc, kappa=kappa) + >>> ticks = [0, 0.15, 0.3] + + The left image contains the Cartesian plot. + + >>> left.plot(x, vonmises_pdf) + >>> left.set_yticks(ticks) + >>> number_of_bins = int(np.sqrt(sample_size)) + >>> left.hist(sample, density=True, bins=number_of_bins) + >>> left.set_title("Cartesian plot") + >>> left.set_xlim(-np.pi, np.pi) + >>> left.grid(True) + + The right image contains the polar plot. + + >>> right.plot(x, vonmises_pdf, label="PDF") + >>> right.set_yticks(ticks) + >>> right.hist(sample, density=True, bins=number_of_bins, + ... label="Histogram") + >>> right.set_title("Polar plot") + >>> right.legend(bbox_to_anchor=(0.15, 1.06)) + + """ + def _shape_info(self): + return [_ShapeInfo("kappa", False, (0, np.inf), (True, False))] + + def _argcheck(self, kappa): + return kappa >= 0 + + def _rvs(self, kappa, size=None, random_state=None): + return random_state.vonmises(0.0, kappa, size=size) + + @inherit_docstring_from(rv_continuous) + def rvs(self, *args, **kwds): + rvs = super().rvs(*args, **kwds) + return np.mod(rvs + np.pi, 2*np.pi) - np.pi + + def _pdf(self, x, kappa): + # vonmises.pdf(x, kappa) = exp(kappa * cos(x)) / (2*pi*I[0](kappa)) + # = exp(kappa * (cos(x) - 1)) / + # (2*pi*exp(-kappa)*I[0](kappa)) + # = exp(kappa * cosm1(x)) / (2*pi*i0e(kappa)) + return np.exp(kappa*sc.cosm1(x)) / (2*np.pi*sc.i0e(kappa)) + + def _logpdf(self, x, kappa): + # vonmises.pdf(x, kappa) = exp(kappa * cosm1(x)) / (2*pi*i0e(kappa)) + return kappa * sc.cosm1(x) - np.log(2*np.pi) - np.log(sc.i0e(kappa)) + + def _cdf(self, x, kappa): + return _stats.von_mises_cdf(kappa, x) + + def _stats_skip(self, kappa): + return 0, None, 0, None + + def _entropy(self, kappa): + # vonmises.entropy(kappa) = -kappa * I[1](kappa) / I[0](kappa) + + # log(2 * np.pi * I[0](kappa)) + # = -kappa * I[1](kappa) * exp(-kappa) / + # (I[0](kappa) * exp(-kappa)) + + # log(2 * np.pi * + # I[0](kappa) * exp(-kappa) / exp(-kappa)) + # = -kappa * sc.i1e(kappa) / sc.i0e(kappa) + + # log(2 * np.pi * i0e(kappa)) + kappa + return (-kappa * sc.i1e(kappa) / sc.i0e(kappa) + + np.log(2 * np.pi * sc.i0e(kappa)) + kappa) + + @extend_notes_in_docstring(rv_continuous, notes="""\ + The default limits of integration are endpoints of the interval + of width ``2*pi`` centered at `loc` (e.g. ``[-pi, pi]`` when + ``loc=0``).\n\n""") + def expect(self, func=None, args=(), loc=0, scale=1, lb=None, ub=None, + conditional=False, **kwds): + _a, _b = -np.pi, np.pi + + if lb is None: + lb = loc + _a + if ub is None: + ub = loc + _b + + return super().expect(func, args, loc, + scale, lb, ub, conditional, **kwds) + + @_call_super_mom + @extend_notes_in_docstring(rv_continuous, notes="""\ + Fit data is assumed to represent angles and will be wrapped onto the + unit circle. `f0` and `fscale` are ignored; the returned shape is + always the maximum likelihood estimate and the scale is always + 1. Initial guesses are ignored.\n\n""") + def fit(self, data, *args, **kwds): + if kwds.pop('superfit', False): + return super().fit(data, *args, **kwds) + + data, fshape, floc, fscale = _check_fit_input_parameters(self, data, + args, kwds) + if self.a == -np.pi: + # vonmises line case, here the default fit method will be used + return super().fit(data, *args, **kwds) + + # wrap data to interval [0, 2*pi] + data = np.mod(data, 2 * np.pi) + + def find_mu(data): + return stats.circmean(data) + + def find_kappa(data, loc): + # Usually, sources list the following as the equation to solve for + # the MLE of the shape parameter: + # r = I[1](kappa)/I[0](kappa), where r = mean resultant length + # This is valid when the location is the MLE of location. + # More generally, when the location may be fixed at an arbitrary + # value, r should be defined as follows: + r = np.sum(np.cos(loc - data))/len(data) + # See gh-18128 for more information. + + # The function r[0](kappa) := I[1](kappa)/I[0](kappa) is monotonic + # increasing from r[0](0) = 0 to r[0](+inf) = 1. The partial + # derivative of the log likelihood function with respect to kappa + # is monotonic decreasing in kappa. + if r == 1: + # All observations are (almost) equal to the mean. Return + # some large kappa such that r[0](kappa) = 1.0 numerically. + return 1e16 + elif r > 0: + def solve_for_kappa(kappa): + return sc.i1e(kappa)/sc.i0e(kappa) - r + + # The bounds of the root of r[0](kappa) = r are derived from + # selected bounds of r[0](x) given in [1, Eq. 11 & 16]. See + # gh-20102 for details. + # + # [1] Amos, D. E. (1973). Computation of Modified Bessel + # Functions and Their Ratios. Mathematics of Computation, + # 28(125): 239-251. + lower_bound = r/(1-r)/(1+r) + upper_bound = 2*lower_bound + + # The bounds are violated numerically for certain values of r, + # where solve_for_kappa evaluated at the bounds have the same + # sign. This indicates numerical imprecision of i1e()/i0e(). + # Return the violated bound in this case as it's more accurate. + if solve_for_kappa(lower_bound) >= 0: + return lower_bound + elif solve_for_kappa(upper_bound) <= 0: + return upper_bound + else: + root_res = root_scalar(solve_for_kappa, method="brentq", + bracket=(lower_bound, upper_bound)) + return root_res.root + else: + # if the provided floc is very far from the circular mean, + # the mean resultant length r can become negative. + # In that case, the equation + # I[1](kappa)/I[0](kappa) = r does not have a solution. + # The maximum likelihood kappa is then 0 which practically + # results in the uniform distribution on the circle. As + # vonmises is defined for kappa > 0, return instead the + # smallest floating point value. + # See gh-18190 for more information + return np.finfo(float).tiny + + # location likelihood equation has a solution independent of kappa + loc = floc if floc is not None else find_mu(data) + # shape likelihood equation depends on location + shape = fshape if fshape is not None else find_kappa(data, loc) + + loc = np.mod(loc + np.pi, 2 * np.pi) - np.pi # ensure in [-pi, pi] + return shape, loc, 1 # scale is not handled + + +vonmises = vonmises_gen(name='vonmises') +vonmises_line = vonmises_gen(a=-np.pi, b=np.pi, name='vonmises_line') + + +class wald_gen(invgauss_gen): + r"""A Wald continuous random variable. + + %(before_notes)s + + Notes + ----- + The probability density function for `wald` is: + + .. math:: + + f(x) = \frac{1}{\sqrt{2\pi x^3}} \exp(- \frac{ (x-1)^2 }{ 2x }) + + for :math:`x >= 0`. + + `wald` is a special case of `invgauss` with ``mu=1``. + + %(after_notes)s + + %(example)s + """ + _support_mask = rv_continuous._open_support_mask + + def _shape_info(self): + return [] + + def _rvs(self, size=None, random_state=None): + return random_state.wald(1.0, 1.0, size=size) + + def _pdf(self, x): + # wald.pdf(x) = 1/sqrt(2*pi*x**3) * exp(-(x-1)**2/(2*x)) + return invgauss._pdf(x, 1.0) + + def _cdf(self, x): + return invgauss._cdf(x, 1.0) + + def _sf(self, x): + return invgauss._sf(x, 1.0) + + def _ppf(self, x): + return invgauss._ppf(x, 1.0) + + def _isf(self, x): + return invgauss._isf(x, 1.0) + + def _logpdf(self, x): + return invgauss._logpdf(x, 1.0) + + def _logcdf(self, x): + return invgauss._logcdf(x, 1.0) + + def _logsf(self, x): + return invgauss._logsf(x, 1.0) + + def _stats(self): + return 1.0, 1.0, 3.0, 15.0 + + def _entropy(self): + return invgauss._entropy(1.0) + + +wald = wald_gen(a=0.0, name="wald") + + +class wrapcauchy_gen(rv_continuous): + r"""A wrapped Cauchy continuous random variable. + + %(before_notes)s + + Notes + ----- + The probability density function for `wrapcauchy` is: + + .. math:: + + f(x, c) = \frac{1-c^2}{2\pi (1+c^2 - 2c \cos(x))} + + for :math:`0 \le x \le 2\pi`, :math:`0 < c < 1`. + + `wrapcauchy` takes ``c`` as a shape parameter for :math:`c`. + + %(after_notes)s + + %(example)s + + """ + def _argcheck(self, c): + return (c > 0) & (c < 1) + + def _shape_info(self): + return [_ShapeInfo("c", False, (0, 1), (False, False))] + + def _pdf(self, x, c): + # wrapcauchy.pdf(x, c) = (1-c**2) / (2*pi*(1+c**2-2*c*cos(x))) + return (1.0-c*c)/(2*np.pi*(1+c*c-2*c*np.cos(x))) + + def _cdf(self, x, c): + + def f1(x, cr): + # CDF for 0 <= x < pi + return 1/np.pi * np.arctan(cr*np.tan(x/2)) + + def f2(x, cr): + # CDF for pi <= x <= 2*pi + return 1 - 1/np.pi * np.arctan(cr*np.tan((2*np.pi - x)/2)) + + cr = (1 + c)/(1 - c) + return _lazywhere(x < np.pi, (x, cr), f=f1, f2=f2) + + def _ppf(self, q, c): + val = (1.0-c)/(1.0+c) + rcq = 2*np.arctan(val*np.tan(np.pi*q)) + rcmq = 2*np.pi-2*np.arctan(val*np.tan(np.pi*(1-q))) + return np.where(q < 1.0/2, rcq, rcmq) + + def _entropy(self, c): + return np.log(2*np.pi*(1-c*c)) + + def _fitstart(self, data): + # Use 0.5 as the initial guess of the shape parameter. + # For the location and scale, use the minimum and + # peak-to-peak/(2*pi), respectively. + if isinstance(data, CensoredData): + data = data._uncensor() + return 0.5, np.min(data), np.ptp(data)/(2*np.pi) + + +wrapcauchy = wrapcauchy_gen(a=0.0, b=2*np.pi, name='wrapcauchy') + + +class gennorm_gen(rv_continuous): + r"""A generalized normal continuous random variable. + + %(before_notes)s + + See Also + -------- + laplace : Laplace distribution + norm : normal distribution + + Notes + ----- + The probability density function for `gennorm` is [1]_: + + .. math:: + + f(x, \beta) = \frac{\beta}{2 \Gamma(1/\beta)} \exp(-|x|^\beta), + + where :math:`x` is a real number, :math:`\beta > 0` and + :math:`\Gamma` is the gamma function (`scipy.special.gamma`). + + `gennorm` takes ``beta`` as a shape parameter for :math:`\beta`. + For :math:`\beta = 1`, it is identical to a Laplace distribution. + For :math:`\beta = 2`, it is identical to a normal distribution + (with ``scale=1/sqrt(2)``). + + References + ---------- + + .. [1] "Generalized normal distribution, Version 1", + https://en.wikipedia.org/wiki/Generalized_normal_distribution#Version_1 + + .. [2] Nardon, Martina, and Paolo Pianca. "Simulation techniques for + generalized Gaussian densities." Journal of Statistical + Computation and Simulation 79.11 (2009): 1317-1329 + + .. [3] Wicklin, Rick. "Simulate data from a generalized Gaussian + distribution" in The DO Loop blog, September 21, 2016, + https://blogs.sas.com/content/iml/2016/09/21/simulate-generalized-gaussian-sas.html + + %(example)s + + """ + def _shape_info(self): + return [_ShapeInfo("beta", False, (0, np.inf), (False, False))] + + def _pdf(self, x, beta): + return np.exp(self._logpdf(x, beta)) + + def _logpdf(self, x, beta): + return np.log(0.5*beta) - sc.gammaln(1.0/beta) - abs(x)**beta + + def _cdf(self, x, beta): + c = 0.5 * np.sign(x) + # evaluating (.5 + c) first prevents numerical cancellation + return (0.5 + c) - c * sc.gammaincc(1.0/beta, abs(x)**beta) + + def _ppf(self, x, beta): + c = np.sign(x - 0.5) + # evaluating (1. + c) first prevents numerical cancellation + return c * sc.gammainccinv(1.0/beta, (1.0 + c) - 2.0*c*x)**(1.0/beta) + + def _sf(self, x, beta): + return self._cdf(-x, beta) + + def _isf(self, x, beta): + return -self._ppf(x, beta) + + def _stats(self, beta): + c1, c3, c5 = sc.gammaln([1.0/beta, 3.0/beta, 5.0/beta]) + return 0., np.exp(c3 - c1), 0., np.exp(c5 + c1 - 2.0*c3) - 3. + + def _entropy(self, beta): + return 1. / beta - np.log(.5 * beta) + sc.gammaln(1. / beta) + + def _rvs(self, beta, size=None, random_state=None): + # see [2]_ for the algorithm + # see [3]_ for reference implementation in SAS + z = random_state.gamma(1/beta, size=size) + y = z ** (1/beta) + # convert y to array to ensure masking support + y = np.asarray(y) + mask = random_state.random(size=y.shape) < 0.5 + y[mask] = -y[mask] + return y + + +gennorm = gennorm_gen(name='gennorm') + + +class halfgennorm_gen(rv_continuous): + r"""The upper half of a generalized normal continuous random variable. + + %(before_notes)s + + See Also + -------- + gennorm : generalized normal distribution + expon : exponential distribution + halfnorm : half normal distribution + + Notes + ----- + The probability density function for `halfgennorm` is: + + .. math:: + + f(x, \beta) = \frac{\beta}{\Gamma(1/\beta)} \exp(-|x|^\beta) + + for :math:`x, \beta > 0`. :math:`\Gamma` is the gamma function + (`scipy.special.gamma`). + + `halfgennorm` takes ``beta`` as a shape parameter for :math:`\beta`. + For :math:`\beta = 1`, it is identical to an exponential distribution. + For :math:`\beta = 2`, it is identical to a half normal distribution + (with ``scale=1/sqrt(2)``). + + References + ---------- + + .. [1] "Generalized normal distribution, Version 1", + https://en.wikipedia.org/wiki/Generalized_normal_distribution#Version_1 + + %(example)s + + """ + def _shape_info(self): + return [_ShapeInfo("beta", False, (0, np.inf), (False, False))] + + def _pdf(self, x, beta): + # beta + # halfgennorm.pdf(x, beta) = ------------- exp(-|x|**beta) + # gamma(1/beta) + return np.exp(self._logpdf(x, beta)) + + def _logpdf(self, x, beta): + return np.log(beta) - sc.gammaln(1.0/beta) - x**beta + + def _cdf(self, x, beta): + return sc.gammainc(1.0/beta, x**beta) + + def _ppf(self, x, beta): + return sc.gammaincinv(1.0/beta, x)**(1.0/beta) + + def _sf(self, x, beta): + return sc.gammaincc(1.0/beta, x**beta) + + def _isf(self, x, beta): + return sc.gammainccinv(1.0/beta, x)**(1.0/beta) + + def _entropy(self, beta): + return 1.0/beta - np.log(beta) + sc.gammaln(1.0/beta) + + +halfgennorm = halfgennorm_gen(a=0, name='halfgennorm') + + +class crystalball_gen(rv_continuous): + r""" + Crystalball distribution + + %(before_notes)s + + Notes + ----- + The probability density function for `crystalball` is: + + .. math:: + + f(x, \beta, m) = \begin{cases} + N \exp(-x^2 / 2), &\text{for } x > -\beta\\ + N A (B - x)^{-m} &\text{for } x \le -\beta + \end{cases} + + where :math:`A = (m / |\beta|)^m \exp(-\beta^2 / 2)`, + :math:`B = m/|\beta| - |\beta|` and :math:`N` is a normalisation constant. + + `crystalball` takes :math:`\beta > 0` and :math:`m > 1` as shape + parameters. :math:`\beta` defines the point where the pdf changes + from a power-law to a Gaussian distribution. :math:`m` is the power + of the power-law tail. + + %(after_notes)s + + .. versionadded:: 0.19.0 + + References + ---------- + .. [1] "Crystal Ball Function", + https://en.wikipedia.org/wiki/Crystal_Ball_function + + %(example)s + """ + def _argcheck(self, beta, m): + """ + Shape parameter bounds are m > 1 and beta > 0. + """ + return (m > 1) & (beta > 0) + + def _shape_info(self): + ibeta = _ShapeInfo("beta", False, (0, np.inf), (False, False)) + im = _ShapeInfo("m", False, (1, np.inf), (False, False)) + return [ibeta, im] + + def _fitstart(self, data): + # Arbitrary, but the default m=1 is not valid + return super()._fitstart(data, args=(1, 1.5)) + + def _pdf(self, x, beta, m): + """ + Return PDF of the crystalball function. + + -- + | exp(-x**2 / 2), for x > -beta + crystalball.pdf(x, beta, m) = N * | + | A * (B - x)**(-m), for x <= -beta + -- + """ + N = 1.0 / (m/beta / (m-1) * np.exp(-beta**2 / 2.0) + + _norm_pdf_C * _norm_cdf(beta)) + + def rhs(x, beta, m): + return np.exp(-x**2 / 2) + + def lhs(x, beta, m): + return ((m/beta)**m * np.exp(-beta**2 / 2.0) * + (m/beta - beta - x)**(-m)) + + return N * _lazywhere(x > -beta, (x, beta, m), f=rhs, f2=lhs) + + def _logpdf(self, x, beta, m): + """ + Return the log of the PDF of the crystalball function. + """ + N = 1.0 / (m/beta / (m-1) * np.exp(-beta**2 / 2.0) + + _norm_pdf_C * _norm_cdf(beta)) + + def rhs(x, beta, m): + return -x**2/2 + + def lhs(x, beta, m): + return m*np.log(m/beta) - beta**2/2 - m*np.log(m/beta - beta - x) + + return np.log(N) + _lazywhere(x > -beta, (x, beta, m), f=rhs, f2=lhs) + + def _cdf(self, x, beta, m): + """ + Return CDF of the crystalball function + """ + N = 1.0 / (m/beta / (m-1) * np.exp(-beta**2 / 2.0) + + _norm_pdf_C * _norm_cdf(beta)) + + def rhs(x, beta, m): + return ((m/beta) * np.exp(-beta**2 / 2.0) / (m-1) + + _norm_pdf_C * (_norm_cdf(x) - _norm_cdf(-beta))) + + def lhs(x, beta, m): + return ((m/beta)**m * np.exp(-beta**2 / 2.0) * + (m/beta - beta - x)**(-m+1) / (m-1)) + + return N * _lazywhere(x > -beta, (x, beta, m), f=rhs, f2=lhs) + + def _ppf(self, p, beta, m): + N = 1.0 / (m/beta / (m-1) * np.exp(-beta**2 / 2.0) + + _norm_pdf_C * _norm_cdf(beta)) + pbeta = N * (m/beta) * np.exp(-beta**2/2) / (m - 1) + + def ppf_less(p, beta, m): + eb2 = np.exp(-beta**2/2) + C = (m/beta) * eb2 / (m-1) + N = 1/(C + _norm_pdf_C * _norm_cdf(beta)) + return (m/beta - beta - + ((m - 1)*(m/beta)**(-m)/eb2*p/N)**(1/(1-m))) + + def ppf_greater(p, beta, m): + eb2 = np.exp(-beta**2/2) + C = (m/beta) * eb2 / (m-1) + N = 1/(C + _norm_pdf_C * _norm_cdf(beta)) + return _norm_ppf(_norm_cdf(-beta) + (1/_norm_pdf_C)*(p/N - C)) + + return _lazywhere(p < pbeta, (p, beta, m), f=ppf_less, f2=ppf_greater) + + def _munp(self, n, beta, m): + """ + Returns the n-th non-central moment of the crystalball function. + """ + N = 1.0 / (m/beta / (m-1) * np.exp(-beta**2 / 2.0) + + _norm_pdf_C * _norm_cdf(beta)) + + def n_th_moment(n, beta, m): + """ + Returns n-th moment. Defined only if n+1 < m + Function cannot broadcast due to the loop over n + """ + A = (m/beta)**m * np.exp(-beta**2 / 2.0) + B = m/beta - beta + rhs = (2**((n-1)/2.0) * sc.gamma((n+1)/2) * + (1.0 + (-1)**n * sc.gammainc((n+1)/2, beta**2 / 2))) + lhs = np.zeros(rhs.shape) + for k in range(n + 1): + lhs += (sc.binom(n, k) * B**(n-k) * (-1)**k / (m - k - 1) * + (m/beta)**(-m + k + 1)) + return A * lhs + rhs + + return N * _lazywhere(n + 1 < m, (n, beta, m), + np.vectorize(n_th_moment, otypes=[np.float64]), + np.inf) + + +crystalball = crystalball_gen(name='crystalball', longname="A Crystalball Function") + + +def _argus_phi(chi): + """ + Utility function for the argus distribution used in the pdf, sf and + moment calculation. + Note that for all x > 0: + gammainc(1.5, x**2/2) = 2 * (_norm_cdf(x) - x * _norm_pdf(x) - 0.5). + This can be verified directly by noting that the cdf of Gamma(1.5) can + be written as erf(sqrt(x)) - 2*sqrt(x)*exp(-x)/sqrt(Pi). + We use gammainc instead of the usual definition because it is more precise + for small chi. + """ + return sc.gammainc(1.5, chi**2/2) / 2 + + +class argus_gen(rv_continuous): + r""" + Argus distribution + + %(before_notes)s + + Notes + ----- + The probability density function for `argus` is: + + .. math:: + + f(x, \chi) = \frac{\chi^3}{\sqrt{2\pi} \Psi(\chi)} x \sqrt{1-x^2} + \exp(-\chi^2 (1 - x^2)/2) + + for :math:`0 < x < 1` and :math:`\chi > 0`, where + + .. math:: + + \Psi(\chi) = \Phi(\chi) - \chi \phi(\chi) - 1/2 + + with :math:`\Phi` and :math:`\phi` being the CDF and PDF of a standard + normal distribution, respectively. + + `argus` takes :math:`\chi` as shape a parameter. Details about sampling + from the ARGUS distribution can be found in [2]_. + + %(after_notes)s + + References + ---------- + .. [1] "ARGUS distribution", + https://en.wikipedia.org/wiki/ARGUS_distribution + .. [2] Christoph Baumgarten "Random variate generation by fast numerical + inversion in the varying parameter case." Research in Statistics, + vol. 1, 2023, doi:10.1080/27684520.2023.2279060. + + .. versionadded:: 0.19.0 + + %(example)s + """ + def _shape_info(self): + return [_ShapeInfo("chi", False, (0, np.inf), (False, False))] + + def _logpdf(self, x, chi): + # for x = 0 or 1, logpdf returns -np.inf + with np.errstate(divide='ignore'): + y = 1.0 - x*x + A = 3*np.log(chi) - _norm_pdf_logC - np.log(_argus_phi(chi)) + return A + np.log(x) + 0.5*np.log1p(-x*x) - chi**2 * y / 2 + + def _pdf(self, x, chi): + return np.exp(self._logpdf(x, chi)) + + def _cdf(self, x, chi): + return 1.0 - self._sf(x, chi) + + def _sf(self, x, chi): + return _argus_phi(chi * np.sqrt(1 - x**2)) / _argus_phi(chi) + + def _rvs(self, chi, size=None, random_state=None): + chi = np.asarray(chi) + if chi.size == 1: + out = self._rvs_scalar(chi, numsamples=size, + random_state=random_state) + else: + shp, bc = _check_shape(chi.shape, size) + numsamples = int(np.prod(shp)) + out = np.empty(size) + it = np.nditer([chi], + flags=['multi_index'], + op_flags=[['readonly']]) + while not it.finished: + idx = tuple((it.multi_index[j] if not bc[j] else slice(None)) + for j in range(-len(size), 0)) + r = self._rvs_scalar(it[0], numsamples=numsamples, + random_state=random_state) + out[idx] = r.reshape(shp) + it.iternext() + + if size == (): + out = out[()] + return out + + def _rvs_scalar(self, chi, numsamples=None, random_state=None): + # if chi <= 1.8: + # use rejection method, see Devroye: + # Non-Uniform Random Variate Generation, 1986, section II.3.2. + # write: PDF f(x) = c * g(x) * h(x), where + # h is [0,1]-valued and g is a density + # we use two ways to write f + # + # Case 1: + # write g(x) = 3*x*sqrt(1-x**2), h(x) = exp(-chi**2 (1-x**2) / 2) + # If X has a distribution with density g its ppf G_inv is given by: + # G_inv(u) = np.sqrt(1 - u**(2/3)) + # + # Case 2: + # g(x) = chi**2 * x * exp(-chi**2 * (1-x**2)/2) / (1 - exp(-chi**2 /2)) + # h(x) = sqrt(1 - x**2), 0 <= x <= 1 + # one can show that + # G_inv(u) = np.sqrt(2*np.log(u*(np.exp(chi**2/2)-1)+1))/chi + # = np.sqrt(1 + 2*np.log(np.exp(-chi**2/2)*(1-u)+u)/chi**2) + # the latter expression is used for precision with small chi + # + # In both cases, the inverse cdf of g can be written analytically, and + # we can apply the rejection method: + # + # REPEAT + # Generate U uniformly distributed on [0, 1] + # Generate X with density g (e.g. via inverse transform sampling: + # X = G_inv(V) with V uniformly distributed on [0, 1]) + # UNTIL X <= h(X) + # RETURN X + # + # We use case 1 for chi <= 0.5 as it maintains precision for small chi + # and case 2 for 0.5 < chi <= 1.8 due to its speed for moderate chi. + # + # if chi > 1.8: + # use relation to the Gamma distribution: if X is ARGUS with parameter + # chi), then Y = chi**2 * (1 - X**2) / 2 has density proportional to + # sqrt(u) * exp(-u) on [0, chi**2 / 2], i.e. a Gamma(3/2) distribution + # conditioned on [0, chi**2 / 2]). Therefore, to sample X from the + # ARGUS distribution, we sample Y from the gamma distribution, keeping + # only samples on [0, chi**2 / 2], and apply the inverse + # transformation X = (1 - 2*Y/chi**2)**(1/2). Since we only + # look at chi > 1.8, gamma(1.5).cdf(chi**2/2) is large enough such + # Y falls in the interval [0, chi**2 / 2] with a high probability: + # stats.gamma(1.5).cdf(1.8**2/2) = 0.644... + # + # The points to switch between the different methods are determined + # by a comparison of the runtime of the different methods. However, + # the runtime is platform-dependent. The implemented values should + # ensure a good overall performance and are supported by an analysis + # of the rejection constants of different methods. + + size1d = tuple(np.atleast_1d(numsamples)) + N = int(np.prod(size1d)) + x = np.zeros(N) + simulated = 0 + chi2 = chi * chi + if chi <= 0.5: + d = -chi2 / 2 + while simulated < N: + k = N - simulated + u = random_state.uniform(size=k) + v = random_state.uniform(size=k) + z = v**(2/3) + # acceptance condition: u <= h(G_inv(v)). This simplifies to + accept = (np.log(u) <= d * z) + num_accept = np.sum(accept) + if num_accept > 0: + # we still need to transform z=v**(2/3) to X = G_inv(v) + rvs = np.sqrt(1 - z[accept]) + x[simulated:(simulated + num_accept)] = rvs + simulated += num_accept + elif chi <= 1.8: + echi = np.exp(-chi2 / 2) + while simulated < N: + k = N - simulated + u = random_state.uniform(size=k) + v = random_state.uniform(size=k) + z = 2 * np.log(echi * (1 - v) + v) / chi2 + # as in case one, simplify u <= h(G_inv(v)) and then transform + # z to the target distribution X = G_inv(v) + accept = (u**2 + z <= 0) + num_accept = np.sum(accept) + if num_accept > 0: + rvs = np.sqrt(1 + z[accept]) + x[simulated:(simulated + num_accept)] = rvs + simulated += num_accept + else: + # conditional Gamma for chi > 1.8 + while simulated < N: + k = N - simulated + g = random_state.standard_gamma(1.5, size=k) + accept = (g <= chi2 / 2) + num_accept = np.sum(accept) + if num_accept > 0: + x[simulated:(simulated + num_accept)] = g[accept] + simulated += num_accept + x = np.sqrt(1 - 2 * x / chi2) + + return np.reshape(x, size1d) + + def _stats(self, chi): + # need to ensure that dtype is float + # otherwise the mask below does not work for integers + chi = np.asarray(chi, dtype=float) + phi = _argus_phi(chi) + m = np.sqrt(np.pi/8) * chi * sc.ive(1, chi**2/4) / phi + # compute second moment, use Taylor expansion for small chi (<= 0.1) + mu2 = np.empty_like(chi) + mask = chi > 0.1 + c = chi[mask] + mu2[mask] = 1 - 3 / c**2 + c * _norm_pdf(c) / phi[mask] + c = chi[~mask] + coef = [-358/65690625, 0, -94/1010625, 0, 2/2625, 0, 6/175, 0, 0.4] + mu2[~mask] = np.polyval(coef, c) + return m, mu2 - m**2, None, None + + +argus = argus_gen(name='argus', longname="An Argus Function", a=0.0, b=1.0) + + +class rv_histogram(rv_continuous): + """ + Generates a distribution given by a histogram. + This is useful to generate a template distribution from a binned + datasample. + + As a subclass of the `rv_continuous` class, `rv_histogram` inherits from it + a collection of generic methods (see `rv_continuous` for the full list), + and implements them based on the properties of the provided binned + datasample. + + Parameters + ---------- + histogram : tuple of array_like + Tuple containing two array_like objects. + The first containing the content of n bins, + the second containing the (n+1) bin boundaries. + In particular, the return value of `numpy.histogram` is accepted. + + density : bool, optional + If False, assumes the histogram is proportional to counts per bin; + otherwise, assumes it is proportional to a density. + For constant bin widths, these are equivalent, but the distinction + is important when bin widths vary (see Notes). + If None (default), sets ``density=True`` for backwards compatibility, + but warns if the bin widths are variable. Set `density` explicitly + to silence the warning. + + .. versionadded:: 1.10.0 + + Notes + ----- + When a histogram has unequal bin widths, there is a distinction between + histograms that are proportional to counts per bin and histograms that are + proportional to probability density over a bin. If `numpy.histogram` is + called with its default ``density=False``, the resulting histogram is the + number of counts per bin, so ``density=False`` should be passed to + `rv_histogram`. If `numpy.histogram` is called with ``density=True``, the + resulting histogram is in terms of probability density, so ``density=True`` + should be passed to `rv_histogram`. To avoid warnings, always pass + ``density`` explicitly when the input histogram has unequal bin widths. + + There are no additional shape parameters except for the loc and scale. + The pdf is defined as a stepwise function from the provided histogram. + The cdf is a linear interpolation of the pdf. + + .. versionadded:: 0.19.0 + + Examples + -------- + + Create a scipy.stats distribution from a numpy histogram + + >>> import scipy.stats + >>> import numpy as np + >>> data = scipy.stats.norm.rvs(size=100000, loc=0, scale=1.5, + ... random_state=123) + >>> hist = np.histogram(data, bins=100) + >>> hist_dist = scipy.stats.rv_histogram(hist, density=False) + + Behaves like an ordinary scipy rv_continuous distribution + + >>> hist_dist.pdf(1.0) + 0.20538577847618705 + >>> hist_dist.cdf(2.0) + 0.90818568543056499 + + PDF is zero above (below) the highest (lowest) bin of the histogram, + defined by the max (min) of the original dataset + + >>> hist_dist.pdf(np.max(data)) + 0.0 + >>> hist_dist.cdf(np.max(data)) + 1.0 + >>> hist_dist.pdf(np.min(data)) + 7.7591907244498314e-05 + >>> hist_dist.cdf(np.min(data)) + 0.0 + + PDF and CDF follow the histogram + + >>> import matplotlib.pyplot as plt + >>> X = np.linspace(-5.0, 5.0, 100) + >>> fig, ax = plt.subplots() + >>> ax.set_title("PDF from Template") + >>> ax.hist(data, density=True, bins=100) + >>> ax.plot(X, hist_dist.pdf(X), label='PDF') + >>> ax.plot(X, hist_dist.cdf(X), label='CDF') + >>> ax.legend() + >>> fig.show() + + """ + _support_mask = rv_continuous._support_mask + + def __init__(self, histogram, *args, density=None, **kwargs): + """ + Create a new distribution using the given histogram + + Parameters + ---------- + histogram : tuple of array_like + Tuple containing two array_like objects. + The first containing the content of n bins, + the second containing the (n+1) bin boundaries. + In particular, the return value of np.histogram is accepted. + density : bool, optional + If False, assumes the histogram is proportional to counts per bin; + otherwise, assumes it is proportional to a density. + For constant bin widths, these are equivalent. + If None (default), sets ``density=True`` for backward + compatibility, but warns if the bin widths are variable. Set + `density` explicitly to silence the warning. + """ + self._histogram = histogram + self._density = density + if len(histogram) != 2: + raise ValueError("Expected length 2 for parameter histogram") + self._hpdf = np.asarray(histogram[0]) + self._hbins = np.asarray(histogram[1]) + if len(self._hpdf) + 1 != len(self._hbins): + raise ValueError("Number of elements in histogram content " + "and histogram boundaries do not match, " + "expected n and n+1.") + self._hbin_widths = self._hbins[1:] - self._hbins[:-1] + bins_vary = not np.allclose(self._hbin_widths, self._hbin_widths[0]) + if density is None and bins_vary: + message = ("Bin widths are not constant. Assuming `density=True`." + "Specify `density` explicitly to silence this warning.") + warnings.warn(message, RuntimeWarning, stacklevel=2) + density = True + elif not density: + self._hpdf = self._hpdf / self._hbin_widths + + self._hpdf = self._hpdf / float(np.sum(self._hpdf * self._hbin_widths)) + self._hcdf = np.cumsum(self._hpdf * self._hbin_widths) + self._hpdf = np.hstack([0.0, self._hpdf, 0.0]) + self._hcdf = np.hstack([0.0, self._hcdf]) + # Set support + kwargs['a'] = self.a = self._hbins[0] + kwargs['b'] = self.b = self._hbins[-1] + super().__init__(*args, **kwargs) + + def _pdf(self, x): + """ + PDF of the histogram + """ + return self._hpdf[np.searchsorted(self._hbins, x, side='right')] + + def _cdf(self, x): + """ + CDF calculated from the histogram + """ + return np.interp(x, self._hbins, self._hcdf) + + def _ppf(self, x): + """ + Percentile function calculated from the histogram + """ + return np.interp(x, self._hcdf, self._hbins) + + def _munp(self, n): + """Compute the n-th non-central moment.""" + integrals = (self._hbins[1:]**(n+1) - self._hbins[:-1]**(n+1)) / (n+1) + return np.sum(self._hpdf[1:-1] * integrals) + + def _entropy(self): + """Compute entropy of distribution""" + res = _lazywhere(self._hpdf[1:-1] > 0.0, + (self._hpdf[1:-1],), + np.log, + 0.0) + return -np.sum(self._hpdf[1:-1] * res * self._hbin_widths) + + def _updated_ctor_param(self): + """ + Set the histogram as additional constructor argument + """ + dct = super()._updated_ctor_param() + dct['histogram'] = self._histogram + dct['density'] = self._density + return dct + + +class studentized_range_gen(rv_continuous): + r"""A studentized range continuous random variable. + + %(before_notes)s + + See Also + -------- + t: Student's t distribution + + Notes + ----- + The probability density function for `studentized_range` is: + + .. math:: + + f(x; k, \nu) = \frac{k(k-1)\nu^{\nu/2}}{\Gamma(\nu/2) + 2^{\nu/2-1}} \int_{0}^{\infty} \int_{-\infty}^{\infty} + s^{\nu} e^{-\nu s^2/2} \phi(z) \phi(sx + z) + [\Phi(sx + z) - \Phi(z)]^{k-2} \,dz \,ds + + for :math:`x ≥ 0`, :math:`k > 1`, and :math:`\nu > 0`. + + `studentized_range` takes ``k`` for :math:`k` and ``df`` for :math:`\nu` + as shape parameters. + + When :math:`\nu` exceeds 100,000, an asymptotic approximation (infinite + degrees of freedom) is used to compute the cumulative distribution + function [4]_ and probability distribution function. + + %(after_notes)s + + References + ---------- + + .. [1] "Studentized range distribution", + https://en.wikipedia.org/wiki/Studentized_range_distribution + .. [2] Batista, Ben Dêivide, et al. "Externally Studentized Normal Midrange + Distribution." Ciência e Agrotecnologia, vol. 41, no. 4, 2017, pp. + 378-389., doi:10.1590/1413-70542017414047716. + .. [3] Harter, H. Leon. "Tables of Range and Studentized Range." The Annals + of Mathematical Statistics, vol. 31, no. 4, 1960, pp. 1122-1147. + JSTOR, www.jstor.org/stable/2237810. Accessed 18 Feb. 2021. + .. [4] Lund, R. E., and J. R. Lund. "Algorithm AS 190: Probabilities and + Upper Quantiles for the Studentized Range." Journal of the Royal + Statistical Society. Series C (Applied Statistics), vol. 32, no. 2, + 1983, pp. 204-210. JSTOR, www.jstor.org/stable/2347300. Accessed 18 + Feb. 2021. + + Examples + -------- + >>> import numpy as np + >>> from scipy.stats import studentized_range + >>> import matplotlib.pyplot as plt + >>> fig, ax = plt.subplots(1, 1) + + Calculate the first four moments: + + >>> k, df = 3, 10 + >>> mean, var, skew, kurt = studentized_range.stats(k, df, moments='mvsk') + + Display the probability density function (``pdf``): + + >>> x = np.linspace(studentized_range.ppf(0.01, k, df), + ... studentized_range.ppf(0.99, k, df), 100) + >>> ax.plot(x, studentized_range.pdf(x, k, df), + ... 'r-', lw=5, alpha=0.6, label='studentized_range pdf') + + Alternatively, the distribution object can be called (as a function) + to fix the shape, location and scale parameters. This returns a "frozen" + RV object holding the given parameters fixed. + + Freeze the distribution and display the frozen ``pdf``: + + >>> rv = studentized_range(k, df) + >>> ax.plot(x, rv.pdf(x), 'k-', lw=2, label='frozen pdf') + + Check accuracy of ``cdf`` and ``ppf``: + + >>> vals = studentized_range.ppf([0.001, 0.5, 0.999], k, df) + >>> np.allclose([0.001, 0.5, 0.999], studentized_range.cdf(vals, k, df)) + True + + Rather than using (``studentized_range.rvs``) to generate random variates, + which is very slow for this distribution, we can approximate the inverse + CDF using an interpolator, and then perform inverse transform sampling + with this approximate inverse CDF. + + This distribution has an infinite but thin right tail, so we focus our + attention on the leftmost 99.9 percent. + + >>> a, b = studentized_range.ppf([0, .999], k, df) + >>> a, b + 0, 7.41058083802274 + + >>> from scipy.interpolate import interp1d + >>> rng = np.random.default_rng() + >>> xs = np.linspace(a, b, 50) + >>> cdf = studentized_range.cdf(xs, k, df) + # Create an interpolant of the inverse CDF + >>> ppf = interp1d(cdf, xs, fill_value='extrapolate') + # Perform inverse transform sampling using the interpolant + >>> r = ppf(rng.uniform(size=1000)) + + And compare the histogram: + + >>> ax.hist(r, density=True, histtype='stepfilled', alpha=0.2) + >>> ax.legend(loc='best', frameon=False) + >>> plt.show() + + """ + + def _argcheck(self, k, df): + return (k > 1) & (df > 0) + + def _shape_info(self): + ik = _ShapeInfo("k", False, (1, np.inf), (False, False)) + idf = _ShapeInfo("df", False, (0, np.inf), (False, False)) + return [ik, idf] + + def _fitstart(self, data): + # Default is k=1, but that is not a valid value of the parameter. + return super()._fitstart(data, args=(2, 1)) + + def _munp(self, K, k, df): + cython_symbol = '_studentized_range_moment' + _a, _b = self._get_support() + # all three of these are used to create a numpy array so they must + # be the same shape. + + def _single_moment(K, k, df): + log_const = _stats._studentized_range_pdf_logconst(k, df) + arg = [K, k, df, log_const] + usr_data = np.array(arg, float).ctypes.data_as(ctypes.c_void_p) + + llc = LowLevelCallable.from_cython(_stats, cython_symbol, usr_data) + + ranges = [(-np.inf, np.inf), (0, np.inf), (_a, _b)] + opts = dict(epsabs=1e-11, epsrel=1e-12) + + return integrate.nquad(llc, ranges=ranges, opts=opts)[0] + + ufunc = np.frompyfunc(_single_moment, 3, 1) + return np.asarray(ufunc(K, k, df), dtype=np.float64)[()] + + def _pdf(self, x, k, df): + + def _single_pdf(q, k, df): + # The infinite form of the PDF is derived from the infinite + # CDF. + if df < 100000: + cython_symbol = '_studentized_range_pdf' + log_const = _stats._studentized_range_pdf_logconst(k, df) + arg = [q, k, df, log_const] + usr_data = np.array(arg, float).ctypes.data_as(ctypes.c_void_p) + ranges = [(-np.inf, np.inf), (0, np.inf)] + + else: + cython_symbol = '_studentized_range_pdf_asymptotic' + arg = [q, k] + usr_data = np.array(arg, float).ctypes.data_as(ctypes.c_void_p) + ranges = [(-np.inf, np.inf)] + + llc = LowLevelCallable.from_cython(_stats, cython_symbol, usr_data) + opts = dict(epsabs=1e-11, epsrel=1e-12) + return integrate.nquad(llc, ranges=ranges, opts=opts)[0] + + ufunc = np.frompyfunc(_single_pdf, 3, 1) + return np.asarray(ufunc(x, k, df), dtype=np.float64)[()] + + def _cdf(self, x, k, df): + + def _single_cdf(q, k, df): + # "When the degrees of freedom V are infinite the probability + # integral takes [on a] simpler form," and a single asymptotic + # integral is evaluated rather than the standard double integral. + # (Lund, Lund, page 205) + if df < 100000: + cython_symbol = '_studentized_range_cdf' + log_const = _stats._studentized_range_cdf_logconst(k, df) + arg = [q, k, df, log_const] + usr_data = np.array(arg, float).ctypes.data_as(ctypes.c_void_p) + ranges = [(-np.inf, np.inf), (0, np.inf)] + + else: + cython_symbol = '_studentized_range_cdf_asymptotic' + arg = [q, k] + usr_data = np.array(arg, float).ctypes.data_as(ctypes.c_void_p) + ranges = [(-np.inf, np.inf)] + + llc = LowLevelCallable.from_cython(_stats, cython_symbol, usr_data) + opts = dict(epsabs=1e-11, epsrel=1e-12) + return integrate.nquad(llc, ranges=ranges, opts=opts)[0] + + ufunc = np.frompyfunc(_single_cdf, 3, 1) + + # clip p-values to ensure they are in [0, 1]. + return np.clip(np.asarray(ufunc(x, k, df), dtype=np.float64)[()], 0, 1) + + +studentized_range = studentized_range_gen(name='studentized_range', a=0, + b=np.inf) + + +class rel_breitwigner_gen(rv_continuous): + r"""A relativistic Breit-Wigner random variable. + + %(before_notes)s + + See Also + -------- + cauchy: Cauchy distribution, also known as the Breit-Wigner distribution. + + Notes + ----- + + The probability density function for `rel_breitwigner` is + + .. math:: + + f(x, \rho) = \frac{k}{(x^2 - \rho^2)^2 + \rho^2} + + where + + .. math:: + k = \frac{2\sqrt{2}\rho^2\sqrt{\rho^2 + 1}} + {\pi\sqrt{\rho^2 + \rho\sqrt{\rho^2 + 1}}} + + The relativistic Breit-Wigner distribution is used in high energy physics + to model resonances [1]_. It gives the uncertainty in the invariant mass, + :math:`M` [2]_, of a resonance with characteristic mass :math:`M_0` and + decay-width :math:`\Gamma`, where :math:`M`, :math:`M_0` and :math:`\Gamma` + are expressed in natural units. In SciPy's parametrization, the shape + parameter :math:`\rho` is equal to :math:`M_0/\Gamma` and takes values in + :math:`(0, \infty)`. + + Equivalently, the relativistic Breit-Wigner distribution is said to give + the uncertainty in the center-of-mass energy :math:`E_{\text{cm}}`. In + natural units, the speed of light :math:`c` is equal to 1 and the invariant + mass :math:`M` is equal to the rest energy :math:`Mc^2`. In the + center-of-mass frame, the rest energy is equal to the total energy [3]_. + + %(after_notes)s + + :math:`\rho = M/\Gamma` and :math:`\Gamma` is the scale parameter. For + example, if one seeks to model the :math:`Z^0` boson with :math:`M_0 + \approx 91.1876 \text{ GeV}` and :math:`\Gamma \approx 2.4952\text{ GeV}` + [4]_ one can set ``rho=91.1876/2.4952`` and ``scale=2.4952``. + + To ensure a physically meaningful result when using the `fit` method, one + should set ``floc=0`` to fix the location parameter to 0. + + References + ---------- + .. [1] Relativistic Breit-Wigner distribution, Wikipedia, + https://en.wikipedia.org/wiki/Relativistic_Breit-Wigner_distribution + .. [2] Invariant mass, Wikipedia, + https://en.wikipedia.org/wiki/Invariant_mass + .. [3] Center-of-momentum frame, Wikipedia, + https://en.wikipedia.org/wiki/Center-of-momentum_frame + .. [4] M. Tanabashi et al. (Particle Data Group) Phys. Rev. D 98, 030001 - + Published 17 August 2018 + + %(example)s + + """ + def _argcheck(self, rho): + return rho > 0 + + def _shape_info(self): + return [_ShapeInfo("rho", False, (0, np.inf), (False, False))] + + def _pdf(self, x, rho): + # C = k / rho**2 + C = np.sqrt( + 2 * (1 + 1/rho**2) / (1 + np.sqrt(1 + 1/rho**2)) + ) * 2 / np.pi + with np.errstate(over='ignore'): + return C / (((x - rho)*(x + rho)/rho)**2 + 1) + + def _cdf(self, x, rho): + # C = k / (2 * rho**2) / np.sqrt(1 + 1/rho**2) + C = np.sqrt(2/(1 + np.sqrt(1 + 1/rho**2)))/np.pi + result = ( + np.sqrt(-1 + 1j/rho) + * np.arctan(x/np.sqrt(-rho*(rho + 1j))) + ) + result = C * 2 * np.imag(result) + # Sometimes above formula produces values greater than 1. + return np.clip(result, None, 1) + + def _munp(self, n, rho): + if n == 1: + # C = k / (2 * rho) + C = np.sqrt( + 2 * (1 + 1/rho**2) / (1 + np.sqrt(1 + 1/rho**2)) + ) / np.pi * rho + return C * (np.pi/2 + np.arctan(rho)) + if n == 2: + # C = pi * k / (4 * rho) + C = np.sqrt( + (1 + 1/rho**2) / (2 * (1 + np.sqrt(1 + 1/rho**2))) + ) * rho + result = (1 - rho * 1j) / np.sqrt(-1 - 1j/rho) + return 2 * C * np.real(result) + else: + return np.inf + + def _stats(self, rho): + # Returning None from stats makes public stats use _munp. + # nan values will be omitted from public stats. Skew and + # kurtosis are actually infinite. + return None, None, np.nan, np.nan + + @inherit_docstring_from(rv_continuous) + def fit(self, data, *args, **kwds): + # Override rv_continuous.fit to better handle case where floc is set. + data, _, floc, fscale = _check_fit_input_parameters( + self, data, args, kwds + ) + + censored = isinstance(data, CensoredData) + if censored: + if data.num_censored() == 0: + # There are no censored values in data, so replace the + # CensoredData instance with a regular array. + data = data._uncensored + censored = False + + if floc is None or censored: + return super().fit(data, *args, **kwds) + + if fscale is None: + # The interquartile range approximates the scale parameter gamma. + # The median approximates rho * gamma. + p25, p50, p75 = np.quantile(data - floc, [0.25, 0.5, 0.75]) + scale_0 = p75 - p25 + rho_0 = p50 / scale_0 + if not args: + args = [rho_0] + if "scale" not in kwds: + kwds["scale"] = scale_0 + else: + M_0 = np.median(data - floc) + rho_0 = M_0 / fscale + if not args: + args = [rho_0] + return super().fit(data, *args, **kwds) + + +rel_breitwigner = rel_breitwigner_gen(a=0.0, name="rel_breitwigner") + + +# Collect names of classes and objects in this module. +pairs = list(globals().copy().items()) +_distn_names, _distn_gen_names = get_distribution_names(pairs, rv_continuous) + +__all__ = _distn_names + _distn_gen_names + ['rv_histogram']