Not mentioned <start>、<end> token

[huosan0123]

In the paper Neural Architectures for Named Entity Recognition, the author mentioned to use token at the beginning of a sequence, and a token at the end of a sequence. In your code I didn't find these two's info. According to a pytorch NER implementation，there are <start> and <end> tokens. By the way, in his implementation of viterbi decode，he take care of first step，to make sure it's <start>, but at tensorflow's code

  trellis[0] = score[0]

  for t in range(1, score.shape[0]):
    v = np.expand_dims(trellis[t - 1], 1) + transition_params
    trellis[t] = score[t] + np.max(v, 0)
    backpointers[t] = np.argmax(v, 0)

I am not sure whether start end is necessary, and whether these two code are right?