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import torch
import torch.nn as nn
import torch.nn.functional as F

class GraphConvolution(Module):
    
    def __init__(self, in_features, out_features, dropout=0., act=F.relu):
        super(GraphConvolution, self).__init__()
        self.in_features = in_features
        self.out_features = out_features
        self.dropout = dropout
        self.act = act
        self.weight = Parameter(torch.FloatTensor(in_features, out_features))
        self.reset_parameters()

    def reset_parameters(self):
        torch.nn.init.xavier_uniform_(self.weight)

    def forward(self, input, adj):
        input = F.dropout(input, self.dropout, self.training)
        support = torch.mm(input, self.weight)
        output = torch.spmm(adj, support)
        output = self.act(output)
        return output

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class GCNModelVAE(nn.Module):
    def __init__(self, input_feat_dim, hidden_dim1, hidden_dim2, dropout):
        super(GCNModelVAE, self).__init__()
        self.gc1 = GraphConvolution(input_feat_dim, hidden_dim1, dropout, act=F.relu)
        self.gc2 = GraphConvolution(hidden_dim1, hidden_dim2, dropout, act=lambda x: x)
        self.gc3 = GraphConvolution(hidden_dim1, hidden_dim2, dropout, act=lambda x: x)
        self.dc = InnerProductDecoder(dropout, act=lambda x: x)

    def encode(self, x, adj):
        hidden1 = self.gc1(x, adj)
        return self.gc2(hidden1, adj), self.gc3(hidden1, adj)

    def reparameterize(self, mu, logvar):
        if self.training:
            std = torch.exp(logvar)
            eps = torch.randn_like(std)
            return eps.mul(std).add_(mu)
        else:
            return mu

    def forward(self, x, adj):
        mu, logvar = self.encode(x, adj)
        z = self.reparameterize(mu, logvar)
        return self.dc(z), mu, logvar

class InnerProductDecoder(nn.Module):
    """Decoder for using inner product for prediction."""

    def __init__(self, dropout, act=torch.sigmoid):
        super(InnerProductDecoder, self).__init__()
        self.dropout = dropout
        self.act = act

    def forward(self, z):
        z = F.dropout(z, self.dropout, training=self.training)
        adj = self.act(torch.mm(z, z.t()))
        return adj

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def loss_function(preds, labels, mu, logvar, n_nodes, norm, pos_weight):
    cost = norm * F.binary_cross_entropy_with_logits(preds, labels, pos_weight=pos_weight)

    # 0.5 * sum(1 + log(sigma^2) - mu^2 - sigma^2)
    KLD = -0.5 / n_nodes * torch.mean(torch.sum(
        1 + 2 * logvar - mu.pow(2) - logvar.exp().pow(2), 1))
    return cost + KLD

pos_weight = float(adj.shape[0] * adj.shape[0] - adj.sum()) / adj.sum()
    norm = adj.shape[0] * adj.shape[0] / float((adj.shape[0] * adj.shape[0] - adj.sum()) * 2)