def EncoderLayer(feature_depth, feedforward_depth, num_heads, dropout, mode):
"""Transformer encoder layer.
The input to the encoder is a pair (embedded source, mask) where
the mask is created from the original source to prevent attending
to the padding part of the input.
Args:
feature_depth: int: depth of embedding
feedforward_depth: int: depth of feed-forward layer
num_heads: int: number of attention heads
dropout: float: dropout rate (how much to drop out)
mode: str: 'train' or 'eval'
Returns:
the layer, returning a pair (actiavtions, mask).
"""
return tl.Serial(
tl.Residual( # Attention block here.
tl.Parallel(tl.LayerNorm(), tl.NoOp()),
tl.MultiHeadedAttention(feature_depth,
num_heads=num_heads,
dropout=dropout,
mode=mode),
tl.Parallel(tl.Dropout(rate=dropout, mode=mode), tl.NoOp())),
tl.Parallel(
ResidualFeedForward(feature_depth,
feedforward_depth,
dropout,
mode=mode),
tl.Div(
divisor=2.0) # Mask added to itself in the residual, divide.
))
def Transformer(vocab_size,
d_feature=512,
d_feedforward=2048,
n_layers=6,
n_heads=8,
dropout=0.1,
max_len=2048,
mode='train'):
"""Transformer.
This model expects on input a pair (source, target).
Args:
vocab_size: int: vocab size (shared source and target).
d_feature: int: depth of embedding
d_feedforward: int: depth of feed-forward layer
n_layers: int: number of encoder/decoder layers
n_heads: int: number of attention heads
dropout: float: dropout rate (how much to drop out)
max_len: int: maximum symbol length for positional encoding
mode: str: 'train' or 'eval'
Returns:
the Transformer model.
"""
positional_embedder = [
tl.Embedding(d_feature, vocab_size),
tl.Dropout(rate=dropout, mode=mode),
tl.PositionalEncoding(max_len=max_len),
]
encoder = [
tl.Branch(positional_embedder, tl.PaddingMask()),
[
EncoderBlock(d_feature, d_feedforward, n_heads, dropout, mode)
for _ in range(n_layers)
],
tl.LayerNorm(),
]
return [
tl.Parallel(tl.NoOp(), tl.ShiftRight()),
tl.Parallel(encoder, positional_embedder),
tl.Select(inputs=(('encoder', 'mask'), 'decoder'),
output=('decoder', ('mask', 'decoder'), 'encoder')),
# (encoder_mask, decoder_input) -> encoder-decoder mask
tl.Parallel(tl.NoOp(), tl.EncoderDecoderMask(), tl.NoOp()),
[
EncoderDecoder(d_feature, d_feedforward, n_heads, dropout, mode)
for _ in range(n_layers)
],
tl.Select(0), # Drop mask and encoder.
tl.LayerNorm(),
tl.Dense(vocab_size),
tl.LogSoftmax(),
]
def Transformer(vocab_size,
feature_depth=512,
feedforward_depth=2048,
num_layers=6,
num_heads=8,
dropout=0.1,
max_len=2048,
mode='train'):
"""Transformer.
This model expects on input a pair (source, target).
Args:
vocab_size: int: vocab size (shared source and target).
feature_depth: int: depth of embedding
feedforward_depth: int: depth of feed-forward layer
num_layers: int: number of encoder/decoder layers
num_heads: int: number of attention heads
dropout: float: dropout rate (how much to drop out)
max_len: int: maximum symbol length for positional encoding
mode: str: 'train' or 'eval'
Returns:
the Transformer model.
"""
embedding = tl.Serial(tl.Embedding(feature_depth, vocab_size),
tl.Dropout(rate=dropout, mode=mode),
tl.PositionalEncoding(max_len=max_len))
encoder = tl.Serial(
tl.Branch(embedding, tl.PaddingMask()),
tl.Serial(*[
EncoderLayer(feature_depth, feedforward_depth, num_heads, dropout,
mode) for _ in range(num_layers)
]), tl.Parallel(tl.LayerNorm(), tl.NoOp()))
stack = [
EncoderDecoderLayer(feature_depth, feedforward_depth, num_heads,
dropout, mode) for _ in range(num_layers)
]
return tl.Serial(
tl.Parallel(tl.NoOp(), tl.ShiftRight()),
tl.Parallel(encoder, embedding),
tl.Select(inputs=(('encoder', 'mask'), 'decoder'),
output=('encoder', ('mask', 'decoder'), 'decoder')),
tl.Parallel( # (encoder_mask, decoder_input) -> encoder-decoder mask
tl.NoOp(), tl.EncoderDecoderMask(), tl.NoOp()),
tl.Serial(*stack),
tl.Select(2), # Drop encoder and mask.
tl.LayerNorm(),
tl.Dense(vocab_size),
tl.LogSoftmax())
def DecoderLayer(feature_depth, feedforward_depth, num_heads, dropout, mode):
"""Transformer decoder layer.
Args:
feature_depth: int: depth of embedding
feedforward_depth: int: depth of feed-forward layer
num_heads: int: number of attention heads
dropout: float: dropout rate (how much to drop out)
mode: str: 'train' or 'eval'
Returns:
the layer.
"""
return tl.Serial(
tl.Residual( # Self-attention block.
tl.LayerNorm(),
tl.Branch(tl.NoOp(), tl.CausalMask(axis=-2)), # Create mask.
tl.MultiHeadedAttention(feature_depth,
num_heads=num_heads,
dropout=dropout,
mode=mode),
tl.Select(0), # Drop the mask.
tl.Dropout(rate=dropout, mode=mode)),
ResidualFeedForward(feature_depth,
feedforward_depth,
dropout,
mode=mode))
def DecoderBlock(d_feature, d_feedforward, n_heads, dropout, mode):
"""Transformer decoder layer.
Args:
d_feature: int: depth of embedding
d_feedforward: int: depth of feed-forward layer
n_heads: int: number of attention heads
dropout: float: dropout rate (how much to drop out)
mode: str: 'train' or 'eval'
Returns:
the layer.
"""
self_attention = [
tl.LayerNorm(),
tl.Branch(tl.NoOp(), tl.CausalMask(axis=-2)), # Create mask.
tl.MultiHeadedAttention(d_feature,
n_heads=n_heads,
dropout=dropout,
mode=mode),
tl.Select(0), # Drop mask.
tl.Dropout(rate=dropout, mode=mode),
]
feed_forward = [
FeedForward(d_feature, d_feedforward, dropout, mode=mode),
]
return [
tl.Residual(self_attention),
tl.Residual(feed_forward),
]
def AtariCnn(hidden_sizes=(32, 32), output_size=128):
# Input's shape = (B, T, H, W, C)
return tl.Serial(
tl.Div(divisor=255.0),
# Have 4 copies of the input, each one shifted to the right by one.
tl.Branch(
tl.NoOp(), tl.ShiftRight(),
tl.Serial(
tl.ShiftRight(),
tl.ShiftRight(),
), tl.Serial(
tl.ShiftRight(),
tl.ShiftRight(),
tl.ShiftRight(),
)),
# Concatenated on the last axis.
tl.Concatenate(axis=-1), # (B, T, H, W, 4C)
tl.Rebatch(tl.Conv(hidden_sizes[0], (5, 5), (2, 2), 'SAME'), 2),
tl.Relu(),
tl.Rebatch(tl.Conv(hidden_sizes[1], (5, 5), (2, 2), 'SAME'), 2),
tl.Relu(),
tl.Flatten(num_axis_to_keep=2), # B, T and rest.
tl.Dense(output_size),
tl.Relu(),
# Eventually this is shaped (B, T, output_size)
)
def EncoderDecoderLayer(feature_depth, feedforward_depth, num_heads, dropout,
mode):
"""Transformer encoder-decoder layer.
The input is a triple pair (encoder, mask, decoder_input) where
the mask is created from the original source to prevent attending
to the padding part of the encoder.
Args:
feature_depth: int: depth of embedding
feedforward_depth: int: depth of feed-forward layer
num_heads: int: number of attention heads
dropout: float: dropout rate (how much to drop out)
mode: str: 'train' or 'eval'
Returns:
the layer, returning a triple (encoder, mask, decoder_activations).
"""
# Decoder self-attending to decoder.
self_attention = tl.Residual(
tl.LayerNorm(),
tl.Branch(tl.NoOp(), tl.CausalMask(axis=-2)), # create mask
tl.MultiHeadedAttention(feature_depth,
num_heads=num_heads,
dropout=dropout,
mode=mode),
tl.Select(0), # drop mask
tl.Dropout(rate=dropout, mode=mode))
# Decoder attending to encoder.
encoder_decoder_attention = tl.Serial(
tl.Select((2, 0, 0, 1)), # (dec, enc, enc, mask)
tl.MultiHeadedAttentionQKV( # (q, k, v, mask) --> new, mask
feature_depth,
num_heads=num_heads,
dropout=dropout,
mode=mode),
tl.Select(0), # drop the mask
tl.Dropout(rate=dropout, mode=mode),
)
return tl.Serial(
tl.Parallel(tl.NoOp(), tl.NoOp(), self_attention),
tl.Branch(tl.NoOp(), encoder_decoder_attention),
tl.Select(inputs=(('encoder', 'mask', 'old_act'), 'new_act'),
output=('encoder', 'mask', ('old_act', 'new_act'))),
tl.Parallel( # Residual after encoder-decoder attention.
tl.NoOp(), tl.NoOp(), tl.Add()),
tl.Parallel( # Feed-forward on the third component (decoder).
tl.NoOp(), tl.NoOp(),
ResidualFeedForward(feature_depth,
feedforward_depth,
dropout,
mode=mode)))
def ChunkedCausalMultiHeadedAttention(d_feature,
n_heads=8,
dropout=0.0,
chunk_selector=None,
mode='train'):
"""Transformer-style causal multi-headed attention operating on chunks.
Accepts inputs that are a list of chunks and applies causal attention.
Args:
d_feature: int: depth of embedding
n_heads: int: number of attention heads
dropout: float: dropout rate
chunk_selector: a function from chunk number to list of chunks to attend.
mode: str: 'train' or 'eval'
Returns:
Multi-headed self-attention layer.
"""
prepare_attention_input = tl.Serial(
tl.Branch(
tl.Branch( # q = k = v = first input
tl.NoOp(), tl.NoOp(), tl.NoOp()),
tl.CausalMask(axis=-2),
),
tl.Parallel(
tl.Parallel(
tl.Dense(d_feature),
tl.Dense(d_feature),
tl.Dense(d_feature),
), tl.NoOp()))
return tl.Serial(
tl.Map(prepare_attention_input),
ChunkedAttentionSelector(selector=chunk_selector), # pylint: disable=no-value-for-parameter
tl.Map(tl.PureMultiHeadedAttention(d_feature=d_feature,
n_heads=n_heads,
dropout=dropout,
mode=mode),
check_shapes=False),
tl.Map(tl.Select(0), check_shapes=False), # drop masks
tl.Map(tl.Dense(d_feature)))
def WideResnetBlock(channels, strides=(1, 1), channel_mismatch=False):
"""WideResnet convolutational block."""
main = tl.Serial(
tl.BatchNorm(),
tl.Relu(),
tl.Conv(channels, (3, 3), strides, padding='SAME'),
tl.BatchNorm(),
tl.Relu(),
tl.Conv(channels, (3, 3), padding='SAME'))
shortcut = tl.NoOp() if not channel_mismatch else tl.Conv(
channels, (3, 3), strides, padding='SAME')
return tl.Residual(main, shortcut=shortcut)
def Residual(*layers, **unused_kwargs):
"""Constructs a residual version of layers, summing input to layers output."""
return tl.Serial(tl.Branch(tl.Serial(*layers), tl.NoOp()), tl.AddAll())
