bc.py

"""
Bilinear Attention Networks
Jin-Hwa Kim, Jaehyun Jun, Byoung-Tak Zhang
https://arxiv.org/abs/1805.07932

This code is written by Jin-Hwa Kim.
"""
from __future__ import print_function
import torch
import torch.nn as nn
from torch.nn.utils.weight_norm import weight_norm
from fc import FCNet


class BCNet(nn.Module):
    """Simple class for non-linear bilinear connect network
    """
    def __init__(self, v_dim, q_dim, h_dim, h_out, act='ReLU', dropout=[.2,.5], k=3):
        super(BCNet, self).__init__()
        
        self.c = 32
        self.k = k
        self.v_dim = v_dim; self.q_dim = q_dim
        self.h_dim = h_dim; self.h_out = h_out

        self.v_net = FCNet([v_dim, h_dim * self.k], act=act, dropout=dropout[0])
        self.q_net = FCNet([q_dim, h_dim * self.k], act=act, dropout=dropout[0])
        self.dropout = nn.Dropout(dropout[1]) # attention
        if 1 < k:
            self.p_net = nn.AvgPool1d(self.k, stride=self.k)
        
        if None == h_out:
            pass
        elif h_out <= self.c:  
            self.h_mat = nn.Parameter(torch.Tensor(1, h_out, 1, h_dim * self.k).normal_())
            self.h_bias = nn.Parameter(torch.Tensor(1, h_out, 1, 1).normal_())
        else:
            self.h_net = weight_norm(nn.Linear(h_dim, h_out), dim=None)

    def forward(self, v, q):
        if None == self.h_out:
            v_ = self.v_net(v)
            q_ = self.q_net(q)
            logits = torch.einsum('bvk,bqk->bvqk', (v_, q_))
            return logits

        # low-rank bilinear pooling using einsum
        elif self.h_out <= self.c:
            v_ = self.dropout(self.v_net(v))
            q_ = self.q_net(q)
            logits = torch.einsum('xhyk,bvk,bqk->bhvq', (self.h_mat, v_, q_)) + self.h_bias
            return logits # b x h_out x v x q

        # batch outer product, linear projection
        # memory efficient but slow computation
        else:
            v_ = self.dropout(self.v_net(v)).transpose(1,2).unsqueeze(3)
            q_ = self.q_net(q).transpose(1,2).unsqueeze(2)
            d_ = torch.matmul(v_, q_) # b x h_dim x v x q
            logits = self.h_net(d_.transpose(1,2).transpose(2,3)) # b x v x q x h_out
            return logits.transpose(2,3).transpose(1,2) # b x h_out x v x q

    def forward_with_weights(self, v, q, w):
        v_ = self.v_net(v) # b x v x d
        q_ = self.q_net(q) # b x q x d
        logits = torch.einsum('bvk,bvq,bqk->bk', (v_, w, q_))
        if 1 < self.k:
            logits = logits.unsqueeze(1) # b x 1 x d
            logits = self.p_net(logits).squeeze(1) * self.k # sum-pooling
        return logits


if __name__=='__main__':
    net = BCNet(1024,1024,1024,1024).cuda()
    x = torch.Tensor(512,36,1024).cuda()
    y = torch.Tensor(512,14,1024).cuda()
    out = net.forward(x,y)