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onmt.py
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onmt.py
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"""Modules imported from OpenNMT"""
import math
import torch
import torch.nn as nn
class MultiHeadedAttention(nn.Module):
""" Multi-Head Attention module originally from OpenNMT"""
def __init__(self, head_count, model_dim, dropout=0.1):
assert model_dim % head_count == 0, \
f"{model_dim} % {head_count} != 0"
self.dim_per_head = model_dim // head_count
self.model_dim = model_dim
super(MultiHeadedAttention, self).__init__()
self.head_count = head_count
self.linear_keys = nn.Linear(model_dim, head_count * self.dim_per_head)
self.linear_values = nn.Linear(model_dim, head_count * self.dim_per_head)
self.linear_query = nn.Linear(model_dim, head_count * self.dim_per_head)
self.softmax = nn.Softmax(dim=-1)
self.dropout = nn.Dropout(dropout)
self.final_linear = nn.Linear(model_dim, model_dim)
def forward(self, key, value, query, mask=None,
layer_cache=None, attn_type=None):
batch_size = key.size(0)
dim_per_head = self.dim_per_head
head_count = self.head_count
# CHECKS
# batch, k_len, d = key.size()
# batch_, k_len_, d_ = value.size()
# aeq(batch, batch_)
# aeq(k_len, k_len_)
# aeq(d, d_)
# batch_, q_len, d_ = query.size()
# aeq(batch, batch_)
# aeq(d, d_)
# aeq(self.model_dim % 8, 0)
# if mask is not None:
# batch_, q_len_, k_len_ = mask.size()
# aeq(batch_, batch)
# aeq(k_len_, k_len)
# aeq(q_len_ == q_len)
# END CHECKS
def shape(x):
"""Projection"""
return x.view(batch_size, -1, head_count, dim_per_head) \
.transpose(1, 2)
def unshape(x):
"""Compute context"""
return x.transpose(1, 2).contiguous() \
.view(batch_size, -1, head_count * dim_per_head)
# 1) Project key, value, and query.
if layer_cache is not None:
if attn_type == "self":
query, key, value = self.linear_query(query), \
self.linear_keys(query), \
self.linear_values(query)
key = shape(key)
value = shape(value)
if layer_cache is not None:
if layer_cache["self_keys"] is not None:
key = torch.cat(
(layer_cache["self_keys"], key),
dim=2)
if layer_cache["self_values"] is not None:
value = torch.cat(
(layer_cache["self_values"], value),
dim=2)
layer_cache["self_keys"] = key
layer_cache["self_values"] = value
elif attn_type == "context":
query = self.linear_query(query)
if layer_cache["memory_keys"] is None:
key, value = self.linear_keys(key), \
self.linear_values(value)
key = shape(key)
value = shape(value)
else:
key, value = layer_cache["memory_keys"], \
layer_cache["memory_values"]
layer_cache["memory_keys"] = key
layer_cache["memory_values"] = value
else:
key = self.linear_keys(key)
value = self.linear_values(value)
query = self.linear_query(query)
key = shape(key)
value = shape(value)
query = shape(query)
key_len = key.size(2)
query_len = query.size(2)
# 2) Calculate and scale scores.
query = query / math.sqrt(dim_per_head)
scores = torch.matmul(query, key.transpose(2, 3)).float()
if mask is not None:
mask = mask.unsqueeze(1) # [B, 1, 1, T_values]
scores = scores.masked_fill(mask.bool(), -1e18)
# 3) Apply attention dropout and compute context vectors.
attn = self.softmax(scores).to(query.dtype)
drop_attn = self.dropout(attn)
context_original = torch.matmul(drop_attn, value)
context = unshape(context_original)
output = self.final_linear(context)
attns = attn.view(batch_size, head_count, query_len, key_len)
# CHECK
# batch_, q_len_, d_ = output.size()
# aeq(q_len, q_len_)
# aeq(batch, batch_)
# aeq(d, d_)
return output, attns
def update_dropout(self, dropout):
self.dropout.p = dropout
class PositionwiseFeedForward(nn.Module):
""" A two-layer Feed-Forward-Network with residual layer norm.
Args:
d_model (int): the size of input for the first-layer of the FFN.
d_ff (int): the hidden layer size of the second-layer
of the FNN.
dropout (float): dropout probability in :math:`[0, 1)`.
"""
def __init__(self, d_model, d_ff, dropout=0.1):
super(PositionwiseFeedForward, self).__init__()
self.w_1 = nn.Linear(d_model, d_ff)
self.w_2 = nn.Linear(d_ff, d_model)
self.layer_norm = nn.LayerNorm(d_model, eps=1e-6)
self.actv = nn.ReLU()
self.dropout_1 = nn.Dropout(dropout)
self.dropout_2 = nn.Dropout(dropout)
def forward(self, x):
inter = self.dropout_1(self.actv(self.w_1(self.layer_norm(x))))
output = self.dropout_2(self.w_2(inter))
return output + x
class AverageAttention(nn.Module):
"""
Average Attention module from
"Accelerating Neural Transformer via an Average Attention Network"
:cite:`DBLP:journals/corr/abs-1805-00631`.
Args:
model_dim (int): the dimension of keys/values/queries,
must be divisible by head_count
dropout (float): dropout parameter
"""
def __init__(self, model_dim, dropout=0.1, aan_useffn=False):
self.model_dim = model_dim
self.aan_useffn = aan_useffn
super(AverageAttention, self).__init__()
if aan_useffn:
self.average_layer = PositionwiseFeedForward(model_dim, model_dim,
dropout)
self.gating_layer = nn.Linear(model_dim * 2, model_dim * 2)
def cumulative_average_mask(self, batch_size, inputs_len, device):
"""
Builds the mask to compute the cumulative average as described in
:cite:`DBLP:journals/corr/abs-1805-00631` -- Figure 3
Args:
batch_size (int): batch size
inputs_len (int): length of the inputs
Returns:
(FloatTensor):
* A Tensor of shape ``(batch_size, input_len, input_len)``
"""
triangle = torch.tril(torch.ones(inputs_len, inputs_len,
dtype=torch.float, device=device))
weights = torch.ones(1, inputs_len, dtype=torch.float, device=device) \
/ torch.arange(1, inputs_len + 1, dtype=torch.float, device=device)
mask = triangle * weights.transpose(0, 1)
return mask.unsqueeze(0).expand(batch_size, inputs_len, inputs_len)
def cumulative_average(self, inputs, mask_or_step,
layer_cache=None, step=None):
"""
Computes the cumulative average as described in
:cite:`DBLP:journals/corr/abs-1805-00631` -- Equations (1) (5) (6)
Args:
inputs (FloatTensor): sequence to average
``(batch_size, input_len, dimension)``
mask_or_step: if cache is set, this is assumed
to be the current step of the
dynamic decoding. Otherwise, it is the mask matrix
used to compute the cumulative average.
layer_cache: a dictionary containing the cumulative average
of the previous step.
Returns:
a tensor of the same shape and type as ``inputs``.
"""
if layer_cache is not None:
step = mask_or_step
average_attention = (inputs + step *
layer_cache["prev_g"]) / (step + 1)
layer_cache["prev_g"] = average_attention
return average_attention
else:
mask = mask_or_step
return torch.matmul(mask.to(inputs.dtype), inputs)
def forward(self, inputs, mask=None, layer_cache=None, step=None):
"""
Args:
inputs (FloatTensor): ``(batch_size, input_len, model_dim)``
Returns:
(FloatTensor, FloatTensor):
* gating_outputs ``(batch_size, input_len, model_dim)``
* average_outputs average attention
``(batch_size, input_len, model_dim)``
"""
batch_size = inputs.size(0)
inputs_len = inputs.size(1)
average_outputs = self.cumulative_average(
inputs, self.cumulative_average_mask(batch_size,
inputs_len, inputs.device)
if layer_cache is None else step, layer_cache=layer_cache)
if self.aan_useffn:
average_outputs = self.average_layer(average_outputs)
gating_outputs = self.gating_layer(torch.cat((inputs,
average_outputs), -1))
input_gate, forget_gate = torch.chunk(gating_outputs, 2, dim=2)
gating_outputs = torch.sigmoid(input_gate) * inputs + \
torch.sigmoid(forget_gate) * average_outputs
return gating_outputs, average_outputs