Merge pull request #79 from 2017alan/master

self-attention module

fastNLP/modules/aggregation/self_attention.py

@@ -5,6 +5,8 @@ import torch.nn.functional as F
 
 
 from fastNLP.modules.utils import initial_parameter
+
+
 class SelfAttention(nn.Module):
     """
     Self Attention Module.
@@ -15,57 +17,53 @@ class SelfAttention(nn.Module):
     num_vec: int, the number of encoded vectors
     """
 
-    def __init__(self, input_size, dim=10, num_vec=10 ,drop = 0.5 ,initial_method =None):
+    def __init__(self, input_size, attention_unit=350, attention_hops=10, drop=0.5, initial_method=None,
+                 use_cuda=False):
         super(SelfAttention, self).__init__()
-        # self.W_s1 = nn.Parameter(torch.randn(dim, input_size), requires_grad=True)
-        # self.W_s2 = nn.Parameter(torch.randn(num_vec, dim), requires_grad=True)
-        self.attention_hops = num_vec
 
-        self.ws1 = nn.Linear(input_size, dim, bias=False)
-        self.ws2 = nn.Linear(dim, num_vec, bias=False)
+        self.attention_hops = attention_hops
+        self.ws1 = nn.Linear(input_size, attention_unit, bias=False)
+        self.ws2 = nn.Linear(attention_unit, attention_hops, bias=False)
+        if use_cuda:
+            self.I = Variable(torch.eye(attention_hops).cuda(), requires_grad=False)
+        else:
+            self.I = Variable(torch.eye(attention_hops), requires_grad=False)
+        self.I_origin = self.I
         self.drop = nn.Dropout(drop)
-        self.softmax = nn.Softmax(dim=2)
         self.tanh = nn.Tanh()
         initial_parameter(self, initial_method)
-    def penalization(self, A):
+
+    def penalization(self, attention):
         """
         compute the penalization term for attention module
         """
-        if self.W_s1.is_cuda:
-            I = Variable(torch.eye(A.size(1)).cuda(), requires_grad=False)
-        else:
-            I = Variable(torch.eye(A.size(1)), requires_grad=False)
-        M = torch.matmul(A, torch.transpose(A, 1, 2)) - I
-        M = M.view(M.size(0), -1)
-        return torch.sum(M ** 2, dim=1)
-        
-    def forward(self, outp ,inp):
-        #  the following code can not be use because some word are padding ,these is not such module!
+        baz = attention.size(0)
+        size = self.I.size()
+        if len(size) != 3 or size[0] != baz:
+            self.I = self.I_origin.expand(baz, -1, -1)
+        attentionT = torch.transpose(attention, 1, 2).contiguous()
+        mat = torch.bmm(attention, attentionT) - self.I[:attention.size(0)]
+        ret = (torch.sum(torch.sum((mat ** 2), 2), 1).squeeze() + 1e-10) ** 0.5
+        return torch.sum(ret) / size[0]
 
-        # inter = self.tanh(torch.matmul(self.W_s1, torch.transpose(x, 1, 2))) # []
-        # A = self.softmax(torch.matmul(self.W_s2, inter))
-        # out = torch.matmul(A, x)
-        # out = out.view(out.size(0), -1)
-        # penalty = self.penalization(A)
-        # return out, penalty
-        outp = outp.contiguous()
-        size = outp.size()  # [bsz, len, nhid]
+    def forward(self, input, input_origin):
+        """
+        :param input:  the matrix to do attention.              [baz, senLen, h_dim]
+        :param inp:  then token index include pad token( 0 )   [baz , senLen]
+        :return output1: the input matrix after attention operation   [baz, multi-head , h_dim]
+        :return output2: the attention penalty term, a scalar  [1]
+        """
+        input = input.contiguous()
+        size = input.size()  # [bsz, len, nhid]
 
-        compressed_embeddings = outp.view(-1, size[2])  # [bsz*len, nhid*2]
-        transformed_inp = torch.transpose(inp, 0, 1).contiguous()  # [bsz, len]
-        transformed_inp = transformed_inp.view(size[0], 1, size[1])  # [bsz, 1, len]
-        concatenated_inp = [transformed_inp for i in range(self.attention_hops)]
-        concatenated_inp = torch.cat(concatenated_inp, 1)  # [bsz, hop, len]
 
-        hbar = self.tanh(self.ws1(self.drop(compressed_embeddings)))  # [bsz*len, attention-unit]
-        attention = self.ws2(hbar).view(size[0], size[1], -1)  # [bsz, len, hop]
-        attention = torch.transpose(attention, 1, 2).contiguous()  # [bsz, hop, len]
-        penalized_alphas = attention + (
-            -10000 * (concatenated_inp == 0).float())
-        # [bsz, hop, len] + [bsz, hop, len]
-        attention = self.softmax(penalized_alphas.view(-1, size[1]))  # [bsz*hop, len]
-        attention = attention.view(size[0], self.attention_hops, size[1])  # [bsz, hop, len]
-        return torch.bmm(attention, outp), attention  # output --> [baz ,hop ,nhid]
+        input_origin = input_origin.expand(self.attention_hops, -1, -1)  # [hops,baz, len]
+        input_origin = input_origin.transpose(0, 1).contiguous()         # [baz, hops,len]
 
+        y1 = self.tanh(self.ws1(self.drop(input)))                       # [baz,len,dim] -->[bsz,len, attention-unit]
+        attention = self.ws2(y1).transpose(1,2).contiguous()             # [bsz,len, attention-unit]--> [bsz, len, hop]--> [baz,hop,len]
 
+        attention = attention + (-999999 * (input_origin == 0).float())  # remove the weight on padding token.
+        attention = F.softmax(attention,2)                               # [baz ,hop, len]
+        return torch.bmm(attention, input), self.penalization(attention) # output1 --> [baz ,hop ,nhid]