def call(self, sequence, training=None):
with bk.framework_(self):
# [batch_size, time_dim]
positions = bk.tile(
bk.expand_dims(bk.arange(sequence.shape[1]), 0),
[sequence.shape[0], 1])
dtype = bk.dtype_universal(positions.dtype)
if dtype not in ('int32', 'int64'):
positions = bk.cast(positions, dtype='int32')
pe = bk.embedding(indices=positions, weight=self.position_encoding)
return pe
def _apply(self, x):
# store last input for deconvolution ops
self._last_input = x
conved = self.convolve(x)
output_shape = K.get_shape(conved)
if not hasattr(self, 'b'):
conved = conved
elif self.untie_biases:
conved += K.expand_dims(self.b, 0)
else:
conved += K.dimshuffle(self.b, ('x', ) * (self.ndim + 1) + (0, ))
activated = self.activation(conved)
K.add_shape(activated, output_shape)
# set shape for output
return activated
def _apply(self, X, h0=None, c0=None, mask=None, **kwargs):
# check input_shape
input_shape = K.get_shape(X)
# ====== check mask ====== #
if mask is not None and (K.ndim(mask) != 2
or K.get_shape(mask)[-1] != input_shape[1]):
raise Exception('Mask must be a 2-D matrix and the time dimension '
'(i.e. the second dimension) must equal to "%d"'
', but the given mask has shape "%s".' %
(input_shape[1], K.get_shape(mask)))
# add broadcastable dimension for mask
if mask is not None:
mask = K.expand_dims(mask, dim=-1)
# ====== initialize states ====== #
# hidden states
h0 = _check_rnn_hidden_states(h0, self, input_shape, 'h0')
c0 = _check_rnn_hidden_states(c0, self, input_shape, 'c0')
# turn off repeat_states if batch_size already included
if K.get_shape(h0)[0] != 1 and K.get_shape(c0)[0] != 1:
self.repeat_states = False
# ====== precompute input ====== #
# linear or norm input mode
if self.input_mode != 'skip':
X = K.dot(X, self.W_in)
if self.input_mode == 'norm':
# normalize all axes except the time dimension
bn = BatchNorm(axes=(0, 1),
activation=K.linear,
gamma_init=self.gamma,
beta_init=self.beta,
mean_init=self.mean,
inv_std_init=self.inv_std)
X = bn(X)
# skip input
elif input_shape[-1] == self.num_units:
X = K.repeat(X, 4, axes=-1)
# ====== compute recurrent output ====== #
out = self._rnn(X,
h0=h0,
c0=c0,
mask=mask,
**self.get_recurrent_info(kwargs))
if not self.return_cell_memory:
out = out[:-1]
for i in out:
K.add_shape(i, shape=input_shape[:-1] + (self.num_units, ))
# only care about the first state
return out[0] if len(out) == 1 else out
def call(self, inputs, training=None):
# anyway, if the smallest value is negative,
# start from 0 (i.e. relative position)
shape = inputs.shape
timestep = shape[1]
y = []
for delay, layer in zip(self.delays, self.all_layers):
start = delay
end = timestep - self.context_length + delay + 1 - self.min_delay
y.append(expand_dims(layer(inputs[:, start:end]), axis=0))
y = concatenate(y, axis=0)
y = self.fn_pooling(y, axis=0)
if isinstance(self.pooling, string_types) and \
'none' in self.pooling.lower() and \
self.context_length == 1:
y = squeeze(y, axis=0)
return y
def _apply(self, x):
if K.ndim(x) != self.conv.ndim + 2:
raise ValueError(
'Input has %d dimensions, but this Ops require %d-D '
'tensor.' % (K.ndim(x), self.conv.ndim + 2))
# ====== prepare the deconvolution ====== #
stride = self.conv.strides
border_mode = self.conv.pad
W = self.conv.W
dilation = self.conv.dilation
# if Dilated Convolution, must transpose the Weights
if self.conv.ndim == 2:
deconv_func = K.deconv2d
elif self.conv.ndim == 3:
deconv_func = K.deconv3d
else:
raise Exception('No support for %d-D input in TransposedConv' %
self.conv.ndim)
# theano require batch_dims is Constant or None, but tensorflow
# require batch_dims is a native TensorVariable
conved = deconv_func(
x,
kernel=W,
output_shape=K.get_shape(
self.conv._last_input,
native=True if K.backend() == 'tensorflow' else False),
strides=stride,
border_mode=border_mode,
filter_dilation=dilation)
if hasattr(self, 'b'):
if self.conv.untie_biases:
conved += K.expand_dims(self.b, 0)
else:
conved += K.dimshuffle(self.b,
('x', ) * (self.conv.ndim + 1) + (0, ))
activated = self.conv.activation(conved)
K.add_shape(activated, self.conv.input_shape)
return activated
def normalize(self, scores):
r""" Normalize attention scores using "fro"-norm that encouraging diversity
among attention heads math::`P = ||A^T*A - I||_2^2` (Kim et al. 2017)
Arguments:
scores: Tensor with shape `[batch_size * num_heads, Tq, Tv]`
"""
# it is easier to assume there is always 1-head at least
num_heads = _get_num_heads(scores)
if num_heads == 0:
return bk.cast(0., scores.dtype)
# [batch_size, num_heads, Tq * Tv]
scoresT = bk.swapaxes(bk.reshape(scores, shape=([0], [1], -1)), 0, 1)
# [batch_size, Tq * Tv, num_heads]
scores = bk.swapaxes(scoresT, 1, 2)
# [batch_size, num_heads, num_heads]
A = bk.matmul(scoresT, scores)
# [batch_size, num_heads, num_heads]
I = bk.eye(num_heads, dtype=A.dtype)
I = bk.expand_dims(I, axis=0)
I = bk.tile(I, reps=A.shape[0], axis=0)
# normalized
P = bk.norm(A - I, p="fro")**2
return P
def align(self,
scores,
value,
query=None,
q_mask=None,
v_mask=None,
causal=False,
residual=False,
dropout=0,
temporal_dropout=False,
sample_shape=1,
temperature=0.5,
training=None):
r"""Applies attention scores to the given value tensor.
Arguments:
scores: Attention Scores float tensor of shape
`[num_heads, batch_size, Tq, Tv]`.
value: Value (or source sequence) tensor of shape
`[num_heads, batch_size, Tv, dim]`.
query: Query (or target sequence) tensor of shape
`[num_heads, batch_size, Tq, dim]`.
q_mask: A boolean query mask `Tensor` of shape `[batch_size, Tq]`.
If given, the output will be zero at the positions where
`mask==False`.
v_mask: A boolean value mask `Tensor` of shape `[batch_size, Tv]`.
If given, will apply the mask such that values at positions where
`mask==False` do not contribute to the result.
dropout : Float. Dropout probability of the attention scores.
temporal_dropout : Boolean. If `True`, using the same dropout mask along
temporal axis (i.e. the 1-st dimension)
sample_shape (`Integer`) : number of mcmc samples for estimating the gradient
of hard attention
temperature: An 0-D `Tensor`, representing the temperature
of a set of RelaxedOneHotCategorical distributions. The temperature
should be positive.
Returns:
attended sequence: Tensor of shape
* `[sample_shape, num_heads, batch_size, Tq, dim]` for (hard + multi-heads)
* `[sample_shape, batch_size, Tq, dim]` for (hard + no-head)
* `[num_heads, batch_size, Tq, dim]` for (soft + multi-heads)
* `[batch_size, Tq, dim]` for (soft + no-head)
attention distribution : for soft attention, return Tensor of shape
* `[num_heads, batch_size, Tq]` for self-attention
* `[num_heads, batch_size, Tq, Tv]` for inter-attention.
for hard attention, return one-hot categorical distribution of shape
* `[sample_shape, num_heads, batch_size, Tq]` for self-attention
* `[sample_shape, num_heads, batch_size, Tq, Tv]` for inter-attention.
if multi-heads attention wasn't used, omit the `[num_heads]`.
"""
num_heads = _get_num_heads(scores)
if num_heads == 0:
Tq = scores.shape[1]
Tv = scores.shape[2]
else:
Tq = scores.shape[2]
Tv = scores.shape[3]
if value is None:
if query is None:
raise ValueError("both query and value are None, "
"at least one of them must be given")
value = query
# ====== Causal mask ====== #
if causal:
# Creates a lower triangular mask, so position i cannot attend to
# positions j>i. This prevents the flow of information from the future
# into the past.
scores_shape = scores.shape
# causal_mask_shape = [1, Tq, Tv].
causal_mask_shape = bk.concatenate(
[bk.ones_like(scores_shape[:-2]), scores_shape[-2:]], axis=0)
causal_mask = bk.tril_mask(causal_mask_shape)
else:
causal_mask = None
if v_mask is not None:
# LocalM applied
if PosLocalM in self:
v_mask = v_mask[:, -Tv:]
# Mask of shape [batch_size, 1, Tv].
v_mask = bk.expand_dims(v_mask, axis=-2)
v_mask = bk.cast(v_mask, 'bool')
if num_heads > 0:
v_mask = bk.expand_dims(v_mask, axis=0)
scores_mask = bk.logical_and(v_mask, causal_mask)
### applying the scores mask
if scores_mask is not None:
padding_mask = bk.logical_not(scores_mask)
# Bias so padding positions do not contribute to attention distribution.
scores -= 1.e9 * bk.cast(padding_mask, dtype=scores.dtype)
# ====== convert attention score to distribution ====== #
# if the last dimension is 1, no point for applying softmax, hence,
# softmax to the second last dimension
### soft attention
if AlignSoft in self:
attention_distribution = bk.softmax(
scores, axis=-2 if scores.shape[-1] == 1 else -1)
### relaxed hard attention
elif AlignRelax in self:
attention_distribution = bay.distributions.RelaxedOneHotCategorical(
temperature=temperature,
logits=bk.squeeze(scores, axis=-1)
if scores.shape[-1] == 1 else scores)
fsample = partial(bay.Distribution.sample,
sample_shape=sample_shape)
attention_distribution = bay.coercible_tensor(
attention_distribution, convert_to_tensor_fn=fsample)
### hard attention
elif AlignHard in self:
attention_distribution = bay.distributions.OneHotCategorical(
logits=bk.squeeze(scores, axis=-1)
if scores.shape[-1] == 1 else scores,
dtype=value.dtype)
fsample = partial(bay.Distribution.sample,
sample_shape=sample_shape)
attention_distribution = bay.coercible_tensor(
attention_distribution, convert_to_tensor_fn=fsample)
# ====== dropout the attention scores ====== #
attention = bk.dropout(attention_distribution,
p_drop=dropout,
axis=1 if temporal_dropout else None,
training=training and dropout > 0)
# ====== applying the attention ====== #
if self.is_self_attention and ScoreLocation in self:
result = bk.expand_dims(bk.array(attention), axis=-1) * value \
if attention.shape[-1] != 1 else \
attention * value
else:
if PosLocalM in self:
value = value[:, -Tv:] if num_heads == 0 else value[:, :, -Tv:]
result = bk.matmul(attention, value)
# ====== applying the Query mask ====== #
if q_mask is not None:
assert q_mask.shape[1] == Tq,\
"Query mask has time dimension %d, but query has time dimension %d" \
% (q_mask.shape[1], Tq)
# Mask of shape [batch_size, Tq, 1].
q_mask = bk.expand_dims(q_mask, axis=-1)
result *= bk.cast(q_mask, dtype=result.dtype)
# ====== residual connection ====== #
if residual:
if query is None:
raise ValueError("query must be given for residual connection")
result += query
# ====== return ====== #
return result, attention_distribution
def score(self,
query,
key=None,
scale=1,
window_width=None,
q_proj=None,
target_proj=None):
r"""
Arguments:
query: Query (or target sequence) tensor of shape
`[batch_size, Tq, dim]` or `[num_heads, batch_size, Tq, dim]` in case
of multi-heads attention.
key: Key (or source sequence) tensor of shape
`[batch_size, Tv, dim]` or `[num_heads, batch_size, Tv, dim]` in case
of multi-heads attention.
scale: single `Scalar` or `Tensor` of shape `[dim]` for scaling
the attention scores, suggested `1/sqrt(dim)` in (Vaswani et al. 2017).
window_width : `None`, `Integer` or `Float` ([0, 1]). The total number of
frames for a single window in local attention (i.e. `left + 1 + right`)
Can be given as a fixed number of frames (`int`), or percentage of
the sequence length (`float`). If `None`, use `Tq`
q_proj : `Dense`, instance of dense or fully connected layer
- for `ScoreLocation`, the number of hidden unit is `1`
- for `ScoreGeneral`, the number of hidden unit is `dim`
target_proj : `Dense`, for predictive local attention, applying
a fully connected network on target sequence (i.e. the query) to
predict the position on source sequence (i.e. the key).
The layer must has output dimension equal to 1 and return logit value.
Returns:
Tensor of shape `[num_heads, batch_size, Tq, Tv]`, or
`[num_heads, batch_size, Tq, 1]` if `ScoreLocation`
"""
### Check if multi-head attention is used
num_heads = _get_num_heads(query)
if num_heads > 0:
query = bk.reshape(query, [-1] + [i for i in query.shape[2:]])
if key is not None:
key = bk.reshape(key, [-1] + [i for i in key.shape[2:]])
Tq = query.shape[1]
Tv = Tq if key is None else key.shape[1]
# scale shape is `[]` or `[dim]`
scale = bk.array(scale, dtype=query.dtype)
### Check the window width
if window_width is None:
window_width = Tq
elif window_width < 1:
window_width = window_width * Tv
window_width = int(window_width)
### Locative attention
if AttentionMechanism.ScoreLocation in self:
if PosLocalM in self or PosLocalP in self:
raise NotImplementedError(
"ScoreLocation only support Global attention, but given: %s"
% str(self))
# [batch_size * num_heads, Tq, dim]
scores = bk.reduce_mean(scale) * q_proj(query)
assert scores.shape[-1] == 1, \
" q_proj must have only 1 hidden unit, but given %d" % scores.shape[-1]
### Other score mode need the key tensor
else:
if key is None:
raise ValueError(
"key must be provided for attention type: %s" % str(self))
### Attention position (local or global)
if PosLocalM in self:
key = key[:, -window_width:]
elif PosLocalP in self:
pt = bk.sigmoid(target_proj(bk.reshape(query, ([0], -1))))
assert pt.shape[-1] == 1, \
"target_proj must project the query [., Tq * dim] to [., 1], i.e. " + \
"predicting the attention position on source sequence using " + \
"knowledge from target sequence."
pt = Tv * pt # `[batch_size * num_heads, 1]`
# `[batch_size * num_heads, Tv]`
# Eq (10) (Luong et al. 2015)
gauss_est = bk.exp(
-bk.square(bk.arange(Tv, dtype=pt.dtype) - pt) /
(2 * bk.square(window_width / 2)))
# `[batch_size * num_heads, 1, Tv]`
gauss_est = bk.expand_dims(gauss_est, axis=1)
### Additive or concat method
if AttentionMechanism.ScoreAdditive in self:
# [batch_size * num_heads, Tq, 1, dim]
q = bk.expand_dims(query, axis=2)
# [batch_size * num_heads, 1, Tv, dim]
k = bk.expand_dims(key, axis=1)
# [batch_size * num_heads, Tq, Tv]
scores = bk.reduce_sum(scale * bk.tanh(q + k), axis=-1)
### Dot product or multiplicative scoring
elif AttentionMechanism.ScoreDotProd in self:
# this is a trick to make attention_scale broadcastable when
# scale_tied=False
scores = bk.matmul(scale * query, bk.swapaxes(key, 1, 2))
### cosine scoring
elif AttentionMechanism.ScoreCosine in self:
# [batch_size * num_heads, Tq, 1, dim]
q = bk.expand_dims(query, axis=2)
# [batch_size * num_heads, 1, Tv, dim]
k = bk.expand_dims(key, axis=1)
# [batch_size * num_heads, Tq, Tv, dim]
scores = (q * k) / (bk.norm(q, p=2) * bk.norm(k, p=2))
scores = bk.reduce_sum(scale * scores, axis=-1, keepdims=False)
### general method with only project on the query
elif AttentionMechanism.ScoreGeneral in self:
query = q_proj(query)
assert query.shape[-1] == key.shape[-1], \
" q_proj must have %d hidden units, but given %d units" % \
(key.shape[-1], query.shape[-1])
scores = bk.matmul(scale * query, bk.swapaxes(key, 1, 2))
else:
raise NotImplementedError(
"No support for attention_type='%s'" % str(self))
### applying the local-predictive attention
if PosLocalP in self:
scores = scores * gauss_est
### get back the multi-heads shape
if num_heads > 0:
scores = bk.reshape(scores,
shape=[num_heads, -1] +
[i for i in scores.shape[1:]])
return scores
