contrib.seq2seq.LuongAttention

tf.contrib.seq2seq.LuongAttention

class tf.contrib.seq2seq.LuongAttention

Defined in tensorflow/contrib/seq2seq/python/ops/attention_wrapper.py.

See the guide: Seq2seq Library (contrib) > Attention

Implements Luong-style (multiplicative) attention scoring.

This attention has two forms. The first is standard Luong attention, as described in:

Minh-Thang Luong, Hieu Pham, Christopher D. Manning. "Effective Approaches to Attention-based Neural Machine Translation." EMNLP 2015. https://arxiv.org/abs/1508.04025

The second is the scaled form inspired partly by the normalized form of Bahdanau attention.

To enable the second form, construct the object with parameter scale=True.

Properties

alignments_size

batch_size

keys

memory_layer

query_layer

values

Methods

__init__

__init__(
    num_units,
    memory,
    memory_sequence_length=None,
    scale=False,
    probability_fn=None,
    score_mask_value=float('-inf'),
    name='LuongAttention'
)

Construct the AttentionMechanism mechanism.

Args:

• num_units: The depth of the attention mechanism.
• memory: The memory to query; usually the output of an RNN encoder. This tensor should be shaped [batch_size, max_time, ...]. memory_sequence_length (optional): Sequence lengths for the batch entries in memory. If provided, the memory tensor rows are masked with zeros for values past the respective sequence lengths.
• scale: Python boolean. Whether to scale the energy term.
• probability_fn: (optional) A callable. Converts the score to probabilities. The default is tf.nn.softmax. Other options include tf.contrib.seq2seq.hardmax and tf.contrib.sparsemax.sparsemax. Its signature should be: probabilities = probability_fn(score).
• score_mask_value: (optional): The mask value for score before passing into probability_fn. The default is -inf. Only used if memory_sequence_length is not None.
• name: Name to use when creating ops.

__call__

__call__(
    query,
    previous_alignments
)

Score the query based on the keys and values.

Args:

• query: Tensor of dtype matching self.values and shape [batch_size, query_depth].
• previous_alignments: Tensor of dtype matching self.values and shape [batch_size, alignments_size] (alignments_size is memory's max_time).

Returns:

• alignments: Tensor of dtype matching self.values and shape [batch_size, alignments_size] (alignments_size is memory's max_time).

Raises:

• ValueError: If key and query depths do not match.

initial_alignments

initial_alignments(
    batch_size,
    dtype
)

Creates the initial alignment values for the AttentionWrapper class.

This is important for AttentionMechanisms that use the previous alignment to calculate the alignment at the next time step (e.g. monotonic attention).

The default behavior is to return a tensor of all zeros.

Args:

• batch_size: int32 scalar, the batch_size.
• dtype: The dtype.

Returns:

A dtype tensor shaped [batch_size, alignments_size] (alignments_size is the values' max_time).