BCECriterion.py 文件源码

def updateGradInput(self, input, target):
         # - (target - input) / ( input (1 - input) )
         # The gradient is slightly incorrect:
         # It should have be divided by (input + self.eps) (1 - input + self.eps)
         # but it is divided by input (1 - input + self.eps) + self.eps
         # This modification requires less memory to be computed.
         if input.nelement() != target.nelement():
            raise RuntimeError("input and target size mismatch")

         self.buffer = self.buffer or input.new()

         buffer = self.buffer
         weights = self.weights
         gradInput = self.gradInput

         if weights is not None and target.dim() != 1:
             weights = self.weights.view(1, target.size(1)).expand_as(target)


         buffer.resize_as_(input)
         # - x ( 1 + self.eps -x ) + self.eps
         torch.add(buffer, input, -1).add_(-self.eps).mul_(input).add_(-self.eps)

         gradInput.resize_as_(input)
         # y - x
         torch.add(gradInput, target, -1, input)
         # - (y - x) / ( x ( 1 + self.eps -x ) + self.eps )
         gradInput.div_(buffer)

         if weights is not None:
             gradInput.mul_(weights)

         if self.sizeAverage:
             gradInput.div_(target.nelement())

         return gradInput