Spaces:
Runtime error
Runtime error
File size: 7,322 Bytes
5672777 |
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 |
# Copyright 2023 The TensorFlow Authors. All Rights Reserved.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
"""Multi-channel Attention."""
# pylint: disable=g-classes-have-attributes
import math
import tensorflow as tf, tf_keras
from official.modeling import tf_utils
from official.nlp.modeling.layers import masked_softmax
class VotingAttention(tf_keras.layers.Layer):
"""Voting Attention layer.
Args:
num_heads: The number of attention heads.
head_size: Per-head hidden size.
kernel_initializer: Initializer for dense layer kernels.
bias_initializer: Initializer for dense layer biases.
kernel_regularizer: Regularizer for dense layer kernels.
bias_regularizer: Regularizer for dense layer biases.
activity_regularizer: Regularizer for dense layer activity.
kernel_constraint: Constraint for dense layer kernels.
bias_constraint: Constraint for dense layer kernels.
"""
def __init__(self,
num_heads,
head_size,
kernel_initializer="glorot_uniform",
bias_initializer="zeros",
kernel_regularizer=None,
bias_regularizer=None,
activity_regularizer=None,
kernel_constraint=None,
bias_constraint=None,
**kwargs):
super().__init__(**kwargs)
self._num_heads = num_heads
self._head_size = head_size
self._kernel_initializer = tf_keras.initializers.get(kernel_initializer)
self._bias_initializer = tf_keras.initializers.get(bias_initializer)
self._kernel_regularizer = tf_keras.regularizers.get(kernel_regularizer)
self._bias_regularizer = tf_keras.regularizers.get(bias_regularizer)
self._kernel_constraint = tf_keras.constraints.get(kernel_constraint)
self._bias_constraint = tf_keras.constraints.get(bias_constraint)
def build(self, unused_input_shapes):
common_kwargs = dict(
kernel_regularizer=self._kernel_regularizer,
bias_regularizer=self._bias_regularizer,
activity_regularizer=self._activity_regularizer,
kernel_constraint=self._kernel_constraint,
bias_constraint=self._bias_constraint)
self._query_dense = tf_keras.layers.EinsumDense(
"BAE,ENH->BANH",
output_shape=(None, self._num_heads, self._head_size),
bias_axes="NH",
name="query",
kernel_initializer=tf_utils.clone_initializer(self._kernel_initializer),
bias_initializer=tf_utils.clone_initializer(self._bias_initializer),
**common_kwargs)
self._key_dense = tf_keras.layers.EinsumDense(
"BAE,ENH->BANH",
output_shape=(None, self._num_heads, self._head_size),
bias_axes="NH",
name="key",
kernel_initializer=tf_utils.clone_initializer(self._kernel_initializer),
bias_initializer=tf_utils.clone_initializer(self._bias_initializer),
**common_kwargs)
super().build(unused_input_shapes)
def call(self, encoder_outputs, doc_attention_mask):
num_docs = tf_utils.get_shape_list(encoder_outputs, expected_rank=[4])[1]
cls_embeddings = encoder_outputs[:, :, 0, :]
key = self._key_dense(cls_embeddings)
query = self._query_dense(cls_embeddings)
doc_attention_mask = tf.cast(doc_attention_mask, tf.float32)
key = tf.einsum("BANH,BA->BANH", key, doc_attention_mask)
query = tf.einsum("BANH,BA->BANH", query, doc_attention_mask)
attention_matrix = tf.einsum("BXNH,BYNH->BNXY", query, key)
mask = tf.ones([num_docs, num_docs])
mask = tf.linalg.set_diag(mask, tf.zeros(num_docs))
attention_matrix = tf.einsum("BNXY,XY->BNXY", attention_matrix, mask)
doc_attention_probs = tf.einsum("BNAY->BNA", attention_matrix)
doc_attention_probs = tf.einsum("BNA->BA", doc_attention_probs)
infadder = (1.0 - doc_attention_mask) * -100000.0
return tf.nn.softmax(doc_attention_probs + infadder)
class MultiChannelAttention(tf_keras.layers.MultiHeadAttention):
"""Multi-channel Attention layer.
Introduced in, [Generating Representative Headlines for News Stories
](https://arxiv.org/abs/2001.09386). Expects multiple cross-attention
target sequences.
Call args:
query: Query `Tensor` of shape `[B, T, dim]`.
value: Value `Tensor` of shape `[B, A, S, dim]`, where A denotes the
context_attention_weights: Context weights of shape `[B, N, T, A]`, where N
is the number of attention heads. Combines multi-channel sources
context tensors according to the distribution among channels.
key: Optional key `Tensor` of shape `[B, A, S, dim]`. If not given, will use
`value` for both `key` and `value`, which is the most common case.
attention_mask: A boolean mask of shape `[B, T, S]`, that prevents attention
to certain positions.
"""
def _build_attention(self, rank):
super()._build_attention(rank) # pytype: disable=attribute-error # typed-keras
self._masked_softmax = masked_softmax.MaskedSoftmax(mask_expansion_axes=[2])
def call(self,
query,
value,
key=None,
context_attention_weights=None,
attention_mask=None):
if not self._built_from_signature:
self._build_from_signature(query, value, key=key)
if key is None:
key = value
# Scalar dimensions referenced here:
# B = batch size (number of stories)
# A = num_docs (number of docs)
# F = target sequence length
# T = source sequence length
# N = `num_attention_heads`
# H = `size_per_head`
# `query_tensor` = [B, F, N ,H]
query_tensor = self._query_dense(query)
# `key_tensor` = [B, A, T, N, H]
key_tensor = self._key_dense(key)
# `value_tensor` = [B, A, T, N, H]
value_tensor = self._value_dense(value)
# Take the dot product between "query" and "key" to get the raw
# attention scores.
attention_scores = tf.einsum("BATNH,BFNH->BANFT", key_tensor, query_tensor)
attention_scores = tf.multiply(attention_scores,
1.0 / math.sqrt(float(self._key_dim)))
# Normalize the attention scores to probabilities.
# `attention_probs` = [B, A, N, F, T]
attention_probs = self._masked_softmax(attention_scores, attention_mask)
# This is actually dropping out entire tokens to attend to, which might
# seem a bit unusual, but is taken from the original Transformer paper.
attention_probs = self._dropout_layer(attention_probs)
# `context_layer` = [B, F, N, H]
context_layer = tf.einsum("BANFT,BATNH->BAFNH", attention_probs,
value_tensor)
attention_output = tf.einsum("BNFA,BAFNH->BFNH", context_attention_weights,
context_layer)
attention_output = self._output_dense(attention_output)
return attention_output
|