layers.py

import math
import torch
import numpy as np
import torch.nn as nn
import torch.nn.functional as F
from torch.nn.parameter import Parameter
from torch.nn.modules.module import Module

class GraphConvolution(Module):
    """
    Simple GCN layer, similar to https://arxiv.org/abs/1609.02907
    """

    def __init__(self, in_features, out_features, bias=True, init='xavier'):
        super(GraphConvolution, self).__init__()
        self.in_features = in_features
        self.out_features = out_features
        self.weight = Parameter(torch.FloatTensor(in_features, out_features))
        if bias:
            self.bias = Parameter(torch.FloatTensor(out_features))
        else:
            self.register_parameter('bias', None)
        if init == 'uniform':
            print("| Uniform Initialization")
            self.reset_parameters_uniform()
        elif init == 'xavier':
            print("| Xavier Initialization")
            self.reset_parameters_xavier()
        elif init == 'kaiming':
            print("| Kaiming Initialization")
            self.reset_parameters_kaiming()
        else:
            raise NotImplementedError

    def reset_parameters_uniform(self):
        stdv = 1. / math.sqrt(self.weight.size(1))
        self.weight.data.uniform_(-stdv, stdv)
        if self.bias is not None:
            self.bias.data.uniform_(-stdv, stdv)

    def reset_parameters_xavier(self):
        nn.init.xavier_normal_(self.weight.data, gain=0.02) # Implement Xavier Uniform
        if self.bias is not None:
            nn.init.constant_(self.bias.data, 0.0)

    def reset_parameters_kaiming(self):
        nn.init.kaiming_normal_(self.weight.data, a=0, mode='fan_in')
        if self.bias is not None:
            nn.init.constant_(self.bias.data, 0.0)

    def forward(self, input, adj):
        support = torch.mm(input, self.weight)
        output = torch.spmm(adj, support)
        if self.bias is not None:
            return output + self.bias
        else:
            return output

    def __repr__(self):
        return self.__class__.__name__ + ' (' \
               + str(self.in_features) + ' -> ' \
               + str(self.out_features) + ')'


class GraphAttention(nn.Module):
    """
    Simple GAT layer, similar to https://arxiv.org/abs/1710.10903
    """

    def __init__(self, in_features, out_features, dropout, alpha, concat=True):
        super(GraphAttention, self).__init__()
        self.dropout = dropout
        self.in_features = in_features
        self.out_features = out_features
        self.alpha = alpha
        self.concat = concat

        self.W = nn.Parameter(nn.init.xavier_normal_(torch.Tensor(in_features, out_features).type(torch.cuda.FloatTensor if torch.cuda.is_available() else torch.FloatTensor), gain=np.sqrt(2.0)), requires_grad=True)
        self.a1 = nn.Parameter(nn.init.xavier_normal_(torch.Tensor(out_features, 1).type(torch.cuda.FloatTensor if torch.cuda.is_available() else torch.FloatTensor), gain=np.sqrt(2.0)), requires_grad=True)
        self.a2 = nn.Parameter(nn.init.xavier_normal_(torch.Tensor(out_features, 1).type(torch.cuda.FloatTensor if torch.cuda.is_available() else torch.FloatTensor), gain=np.sqrt(2.0)), requires_grad=True)

        self.leakyrelu = nn.LeakyReLU(self.alpha)

    def forward(self, input, adj):
        h = torch.mm(input, self.W)
        N = h.size()[0]

        f_1 = torch.matmul(h, self.a1)
        f_2 = torch.matmul(h, self.a2)
        e = self.leakyrelu(f_1 + f_2.transpose(0,1))

        zero_vec = -9e15*torch.ones_like(e)
        attention = torch.where(adj > 0, e, zero_vec)
        attention = F.softmax(attention, dim=1)
        attention = F.dropout(attention, self.dropout, training=self.training)
        h_prime = torch.matmul(attention, h)

        if self.concat:
            return F.elu(h_prime)
        else:
            return h_prime

    def __repr__(self):
        return self.__class__.__name__ + ' (' + str(self.in_features) + ' -> ' + str(self.out_features) + ')'