ctc_theano.py 文件源码

def _editdist(s, t):
        """
        Levenshtein's edit distance function
        :param s: vector, source string
        :param t: vector, target string
        :return:  edit distance, scalar
        """
        def update(x, previous_row):
            current_row = previous_row + 1
            current_row = tensor.set_subtensor(current_row[1:], tensor.minimum(current_row[1:], tensor.add(previous_row[:-1], tensor.neq(target,x))))
            current_row = tensor.set_subtensor(current_row[1:], tensor.minimum(current_row[1:], current_row[0:-1] + 1))
            return current_row
        source, target = ifelse(tensor.lt(s.shape[0], t.shape[0]), (t, s), (s, t))
        previous_row = tensor.arange(target.size + 1, dtype=theano.config.floatX)
        result, updates = theano.scan(fn=update, sequences=source, outputs_info=previous_row, name='editdist')
        return result[-1,-1]