net.py 文件源码

def attend(self, query, key, value, mask, minfs=None):
        """
        Input shapes:
            q=(b, units, dec_l), k=(b, units, enc_l),
            v=(b, units, dec_l, enc_l), m=(b, dec_l, enc_l)
        """

        # Calculate Attention Scores with Mask for Zero-padded Areas
        pre_a = F.batch_matmul(query, key, transa=True)  # (b, dec_l, enc_l)
        minfs = self.xp.full(pre_a.shape, -np.inf, pre_a.dtype) \
            if minfs is None else minfs
        pre_a = F.where(mask, pre_a, minfs)
        a = F.softmax(pre_a, axis=2)
        # if values in axis=2 are all -inf, they become nan. thus do re-mask.
        a = F.where(self.xp.isnan(a.data),
                    self.xp.zeros(a.shape, dtype=a.dtype), a)
        reshaped_a = a[:, None]  # (b, 1, dec_xl, enc_l)

        # Calculate Weighted Sum
        pre_c = F.broadcast_to(reshaped_a, value.shape) * value
        c = F.sum(pre_c, axis=3, keepdims=True)  # (b, units, dec_xl, 1)
        return c