seq2seq.py 文件源码

def sequence_loss(logits,
                  targets,
                  weights,
                  average_across_timesteps=True,
                  average_across_batch=True,
                  softmax_loss_function=None,
                  name=None):
  """Weighted cross-entropy loss for a sequence of logits, batch-collapsed.

  Args:
    logits: List of 2D Tensors of shape [batch_size x num_decoder_symbols].
    targets: List of 1D batch-sized int32 Tensors of the same length as logits.
    weights: List of 1D batch-sized float-Tensors of the same length as logits.
    average_across_timesteps: If set, divide the returned cost by the total
      label weight.
    average_across_batch: If set, divide the returned cost by the batch size.
    softmax_loss_function: Function (labels-batch, inputs-batch) -> loss-batch
      to be used instead of the standard softmax (the default if this is None).
    name: Optional name for this operation, defaults to "sequence_loss".

  Returns:
    A scalar float Tensor: The average log-perplexity per symbol (weighted).

  Raises:
    ValueError: If len(logits) is different from len(targets) or len(weights).
  """
  with ops.name_scope(name, "sequence_loss", logits + targets + weights):
    cost = math_ops.reduce_sum(
        sequence_loss_by_example(
            logits,
            targets,
            weights,
            average_across_timesteps=average_across_timesteps,
            softmax_loss_function=softmax_loss_function))
    if average_across_batch:
      batch_size = array_ops.shape(targets[0])[0]
      return cost / math_ops.cast(batch_size, cost.dtype)
    else:
      return cost