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import torch
import torch.nn as nn
import torch.nn.functional as F
import dgl
import dgl.function as fn
import numpy as np
"""
Graph Transformer Layer
"""
"""
Util functions
"""
def src_dot_dst(src_field, dst_field, out_field):
def func(edges):
return {
out_field: (edges.src[src_field] * edges.dst[dst_field]).sum(
-1, keepdim=True
)
}
return func
def scaled_exp(field, scale_constant):
def func(edges):
# clamp for softmax numerical stability
return {field: torch.exp((edges.data[field] / scale_constant).clamp(-5, 5))}
return func
"""
Single Attention Head
"""
class MultiHeadAttentionLayer(nn.Module):
def __init__(self, in_dim, out_dim, num_heads, use_bias):
super().__init__()
self.out_dim = out_dim
self.num_heads = num_heads
if use_bias:
self.Q = nn.Linear(in_dim, out_dim * num_heads, bias=True)
self.K = nn.Linear(in_dim, out_dim * num_heads, bias=True)
self.V = nn.Linear(in_dim, out_dim * num_heads, bias=True)
else:
self.Q = nn.Linear(in_dim, out_dim * num_heads, bias=False)
self.K = nn.Linear(in_dim, out_dim * num_heads, bias=False)
self.V = nn.Linear(in_dim, out_dim * num_heads, bias=False)
def propagate_attention(self, g):
# Compute attention score
g.apply_edges(src_dot_dst("K_h", "Q_h", "score")) # , edges)
g.apply_edges(scaled_exp("score", np.sqrt(self.out_dim)))
# Send weighted values to target nodes
eids = g.edges()
g.send_and_recv(eids, fn.u_mul_e("V_h", "score", "V_h"), fn.sum("V_h", "wV"))
g.send_and_recv(eids, fn.copy_e("score", "score"), fn.sum("score", "z"))
def forward(self, g, h):
Q_h = self.Q(h)
K_h = self.K(h)
V_h = self.V(h)
# Reshaping into [num_nodes, num_heads, feat_dim] to
# get projections for multi-head attention
g.ndata["Q_h"] = Q_h.view(-1, self.num_heads, self.out_dim)
g.ndata["K_h"] = K_h.view(-1, self.num_heads, self.out_dim)
g.ndata["V_h"] = V_h.view(-1, self.num_heads, self.out_dim)
self.propagate_attention(g)
g.ndata["z"] = g.ndata["z"].tile((1, 1, self.out_dim))
mask_empty = g.ndata["z"] > 0
head_out = g.ndata["wV"]
head_out[mask_empty] = head_out[mask_empty] / (g.ndata["z"][mask_empty])
g.ndata["z"] = g.ndata["z"][:, :, 0].view(
g.ndata["wV"].shape[0], self.num_heads, 1
)
return head_out
class GraphTransformerLayer(nn.Module):
"""
Param:
"""
def __init__(
self,
in_dim,
out_dim,
num_heads,
dropout=0.0,
layer_norm=False,
batch_norm=True,
residual=True,
use_bias=False,
):
super().__init__()
self.in_channels = in_dim
self.out_channels = out_dim
self.num_heads = num_heads
self.dropout = dropout
self.residual = residual
self.layer_norm = layer_norm
self.batch_norm = batch_norm
self.attention = MultiHeadAttentionLayer(
in_dim, out_dim // num_heads, num_heads, use_bias
)
self.O = nn.Linear(out_dim, out_dim)
if self.layer_norm:
self.layer_norm1 = nn.LayerNorm(out_dim)
if self.batch_norm:
self.batch_norm1 = nn.BatchNorm1d(out_dim)
# FFN
self.FFN_layer1 = nn.Linear(out_dim, out_dim * 2)
self.FFN_layer2 = nn.Linear(out_dim * 2, out_dim)
if self.layer_norm:
self.layer_norm2 = nn.LayerNorm(out_dim)
if self.batch_norm:
self.batch_norm2 = nn.BatchNorm1d(out_dim)
def forward(self, g, h):
h_in1 = h # for first residual connection
# multi-head attention out
attn_out = self.attention(g, h)
h = attn_out.view(-1, self.out_channels)
h = F.dropout(h, self.dropout, training=self.training)
h = self.O(h)
if self.residual:
h = h_in1 + h # residual connection
if self.layer_norm:
h = self.layer_norm1(h)
if self.batch_norm:
h = self.batch_norm1(h)
h_in2 = h # for second residual connection
# FFN
h = self.FFN_layer1(h)
h = F.relu(h)
h = F.dropout(h, self.dropout, training=self.training)
h = self.FFN_layer2(h)
if self.residual:
h = h_in2 + h # residual connection
if self.layer_norm:
h = self.layer_norm2(h)
if self.batch_norm:
h = self.batch_norm2(h)
return h
def __repr__(self):
return "{}(in_channels={}, out_channels={}, heads={}, residual={})".format(
self.__class__.__name__,
self.in_channels,
self.out_channels,
self.num_heads,
self.residual,
)
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