model.py 文件源码

def viterbi_decode(self, logits, lens):
        """Borrowed from pytorch tutorial

        Arguments:
            logits: [batch_size, seq_len, n_labels] FloatTensor
            lens: [batch_size] LongTensor
        """
        batch_size, seq_len, n_labels = logits.size()
        vit = logits.data.new(batch_size, self.n_labels).fill_(-10000)
        vit[:, self.start_idx] = 0
        vit = Variable(vit)
        c_lens = lens.clone()

        logits_t = logits.transpose(1, 0)
        pointers = []
        for logit in logits_t:
            vit_exp = vit.unsqueeze(1).expand(batch_size, n_labels, n_labels)
            trn_exp = self.transitions.unsqueeze(0).expand_as(vit_exp)
            vit_trn_sum = vit_exp + trn_exp
            vt_max, vt_argmax = vit_trn_sum.max(2)

            vt_max = vt_max.squeeze(-1)
            vit_nxt = vt_max + logit
            pointers.append(vt_argmax.squeeze(-1).unsqueeze(0))

            mask = (c_lens > 0).float().unsqueeze(-1).expand_as(vit_nxt)
            vit = mask * vit_nxt + (1 - mask) * vit

            mask = (c_lens == 1).float().unsqueeze(-1).expand_as(vit_nxt)
            vit += mask * self.transitions[ self.stop_idx ].unsqueeze(0).expand_as(vit_nxt)

            c_lens = c_lens - 1

        pointers = torch.cat(pointers)
        scores, idx = vit.max(1)
        idx = idx.squeeze(-1)
        paths = [idx.unsqueeze(1)]

        for argmax in reversed(pointers):
            idx_exp = idx.unsqueeze(-1)
            idx = torch.gather(argmax, 1, idx_exp)
            idx = idx.squeeze(-1)

            paths.insert(0, idx.unsqueeze(1))

        paths = torch.cat(paths[1:], 1)
        scores = scores.squeeze(-1)

        return scores, paths