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[文档]def sequence_mask(seq_ids, valid_lengths):
To boost the performance, this sequence_mask is different with paddle.nn.functional.sequence_mask
The whole sequence index, a tensor with a shape of [batch_size, sequence_length].
The valid length of every sequence, a tensor with a shape of [batch_size].
Tensor: Returns the output sequence mask `mask`.
Its dtype is `bool` and has a shape of [batch_size, sequence_length].
lengths_exp = valid_lengths.unsqueeze(1)
mask = seq_ids < lengths_exp