def PositionalEncoding(mode,
dropout=None,
max_len=None,
axial_pos_shape=None,
d_axial_pos_embs=None):
"""Returns the positional encoding layer depending on the arguments."""
if not axial_pos_shape:
positional_encoding = tl.PositionalEncoding(max_len=max_len,
dropout=dropout,
mode=mode)
elif axial_pos_shape == 'fixed-base': # TODO(lukaszkaiser): remove this HACK
positional_encoding = tl.FixedBasePositionalEncoding(mode=mode)
elif axial_pos_shape == 'infinite': # TODO(lukaszkaiser): remove this HACK
positional_encoding = tl.InfinitePositionalEncoding(affine=False)
elif axial_pos_shape == 'infinite-affine':
# TODO(lukaszkaiser): remove this HACK
positional_encoding = tl.InfinitePositionalEncoding()
elif axial_pos_shape == 'time-bin': # TODO(lukaszkaiser): remove this HACK
positional_encoding = tl.TimeBinPositionalEncoding()
else:
assert d_axial_pos_embs is not None
positional_encoding = tl.AxialPositionalEncoding(
shape=axial_pos_shape,
d_embs=d_axial_pos_embs,
dropout_broadcast_dims=tuple(range(1,
len(axial_pos_shape) + 1)),
dropout=dropout,
mode=mode)
return positional_encoding
def PositionalEncoder(mode,
dropout=None,
max_len=None,
pos_type=None,
pos_axial_shape=None,
pos_d_axial_embs=None,
pos_start_from_zero_prob=1.0,
pos_max_offset_to_add=0,
use_bfloat16=False):
"""Returns the positional encoding layer depending on the arguments.
Args:
mode: If `'predict'`, use fast inference. If `'train'`, each encoder/decoder
block will include dropout; else, it will pass all values through
unaltered.
dropout: Stochastic rate (probability) for dropping an activation
value when applying dropout after the embedding block.
max_len: Maximum symbol length for positional encoding.
pos_type: string, the type of positional embeddings to use.
pos_axial_shape: tuple of ints: input shape to use for the axial position
encoding. If unset, axial position encoding is disabled.
pos_d_axial_embs: tuple of ints: depth of position embedding for each axis.
Tuple length must match pos_axial_shape, and values must sum to d_model.
pos_start_from_zero_prob: how often to start from 0 during training,
(if 1.0, we always start from position 0, if less, we randomize).
pos_max_offset_to_add: maximum offset to add to positions during training
when randomizing; this offset plus input length must still be less than
max_len for all training examples.
use_bfloat16: If `True`, use bfloat16 weights instead of the default
float32; this can save memory but may (rarely) lead to numerical issues.
Returns:
A layer that will do the positional encoding.
"""
if not pos_type:
positional_encoding = tl.PositionalEncoding(
max_len=max_len, dropout=dropout, use_bfloat16=use_bfloat16,
start_from_zero_prob=pos_start_from_zero_prob,
max_offset_to_add=pos_max_offset_to_add, mode=mode)
elif pos_type == 'sin-cos':
positional_encoding = tl.SinCosPositionalEncoding(mode=mode)
elif pos_type == 'fixed-base':
positional_encoding = tl.FixedBasePositionalEncoding(mode=mode)
elif pos_type == 'infinite':
positional_encoding = tl.InfinitePositionalEncoding(affine=False)
elif pos_type == 'infinite-affine':
positional_encoding = tl.InfinitePositionalEncoding()
elif pos_type == 'time-bin':
positional_encoding = tl.TimeBinPositionalEncoding()
elif pos_type == 'no':
positional_encoding = tl.Serial() # no positional encoding at all
else: # TODO(lukaszkaiser): name this type and check for the correct name
assert pos_d_axial_embs is not None
positional_encoding = tl.AxialPositionalEncoding(
shape=pos_axial_shape, d_embs=pos_d_axial_embs,
dropout_broadcast_dims=tuple(range(1, len(pos_axial_shape) + 1)),
dropout=dropout, mode=mode)
return positional_encoding
def PositionalEncoder(mode,
dropout=None,
max_len=None,
axial_pos_shape=None,
d_axial_pos_embs=None,
use_bfloat16=False):
"""Returns the positional encoding layer depending on the arguments.
Args:
mode: If `'predict'`, use fast inference. If `'train'`, each encoder/decoder
block will include dropout; else, it will pass all values through
unaltered.
dropout: Stochastic rate (probability) for dropping an activation
value when applying dropout after the embedding block.
max_len: Maximum symbol length for positional encoding.
axial_pos_shape: tuple of ints: input shape to use for the axial position
encoding. If unset, axial position encoding is disabled.
d_axial_pos_embs: tuple of ints: depth of position embedding for each axis.
Tuple length must match axial_pos_shape, and values must sum to d_model.
use_bfloat16: If `True`, use bfloat16 weights instead of the default
float32; this can save memory but may (rarely) lead to numerical issues.
Returns:
A layer that will do the positional encoding.
"""
if not axial_pos_shape:
positional_encoding = tl.PositionalEncoding(max_len=max_len,
dropout=dropout,
mode=mode,
use_bfloat16=use_bfloat16)
elif axial_pos_shape == 'sin-cos': # TODO(lukaszkaiser): remove this HACK
positional_encoding = tl.SinCosPositionalEncoding(mode=mode)
elif axial_pos_shape == 'fixed-base': # TODO(lukaszkaiser): remove this HACK
positional_encoding = tl.FixedBasePositionalEncoding(mode=mode)
elif axial_pos_shape == 'infinite': # TODO(lukaszkaiser): remove this HACK
positional_encoding = tl.InfinitePositionalEncoding(affine=False)
elif axial_pos_shape == 'infinite-affine':
# TODO(lukaszkaiser): remove this HACK
positional_encoding = tl.InfinitePositionalEncoding()
elif axial_pos_shape == 'time-bin': # TODO(lukaszkaiser): remove this HACK
positional_encoding = tl.TimeBinPositionalEncoding()
else:
assert d_axial_pos_embs is not None
positional_encoding = tl.AxialPositionalEncoding(
shape=axial_pos_shape,
d_embs=d_axial_pos_embs,
dropout_broadcast_dims=tuple(range(1,
len(axial_pos_shape) + 1)),
dropout=dropout,
mode=mode)
return positional_encoding
def ReformerLM(vocab_size,
d_model=512,
d_ff=2048,
d_attention_key=64,
d_attention_value=64,
n_layers=6,
n_heads=8,
dropout=0.1,
max_len=2048,
n_chunks=0,
n_attention_chunks=1,
attention_type=tl.DotProductCausalAttention,
share_qk=False,
axial_pos_shape=(),
d_axial_pos_embs=None,
ff_activation=tl.FastGelu,
ff_use_sru=0,
ff_chunk_size=0,
mode='train'):
"""Reversible transformer language model (only uses a decoder, no encoder).
Args:
vocab_size: int: vocab size
d_model: int: depth of *each half* of the two-part features
d_ff: int: depth of feed-forward layer
d_attention_key: int: depth of key vector for each attention head
d_attention_value: int: depth of value vector for each attention head
n_layers: int: number of 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
n_chunks: int: number of chunks (must match input pipeline)
n_attention_chunks: int: number of chunks for attention
attention_type: class: attention class to use, such as DotProductAttention.
share_qk: bool, whether to share queries and keys.
axial_pos_shape: tuple of ints: input shape to use for the axial position
encoding. If unset, axial position encoding is disabled.
d_axial_pos_embs: tuple of ints: depth of position embedding for each axis.
Tuple length must match axial_pos_shape, and values must sum to d_model.
ff_activation: the non-linearity in feed-forward layer
ff_use_sru: int; if > 0, we use this many SRU layers instead of feed-forward
ff_chunk_size: int; if > 0, chunk feed-forward into this-sized chunks
mode: str: 'train', 'eval', or 'predict'
Returns:
the layer.
"""
if n_chunks == 0:
n_chunks = 1
concatenate_input_chunks = []
else:
concatenate_input_chunks = tl.Concatenate(n_items=n_chunks)
d_emb = d_model
if not axial_pos_shape:
positional_encoding = tl.PositionalEncoding(
max_len=max_len, dropout=dropout, mode=mode)
elif axial_pos_shape == 'fixed-base': # TODO(lukaszkaiser): remove this HACK
positional_encoding = tl.FixedBasePositionalEncoding(mode=mode)
d_emb //= 2
elif axial_pos_shape == 'infinite': # TODO(lukaszkaiser): remove this HACK
positional_encoding = tl.InfinitePositionalEncoding(affine=False)
elif axial_pos_shape == 'infinite-affine':
# TODO(lukaszkaiser): remove this HACK
positional_encoding = tl.InfinitePositionalEncoding()
elif axial_pos_shape == 'time-bin': # TODO(lukaszkaiser): remove this HACK
positional_encoding = tl.TimeBinPositionalEncoding()
else:
assert d_axial_pos_embs is not None
positional_encoding = tl.AxialPositionalEncoding(
shape=axial_pos_shape, d_embs=d_axial_pos_embs,
dropout_broadcast_dims=tuple(range(1, len(axial_pos_shape) + 1)),
dropout=dropout, mode=mode)
positional_embedder = [
tl.Embedding(d_emb, vocab_size),
BroadcastedDropout(rate=dropout, mode=mode), # pylint: disable=no-value-for-parameter
positional_encoding,
]
decoder_blocks = []
if isinstance(attention_type, (tuple, list)):
assert n_layers % len(attention_type) == 0
else:
attention_type = [attention_type]
for layer_idx in range(n_layers):
layer_attention_type = attention_type[layer_idx % len(attention_type)]
decoder_block = DecoderBlock(
d_model, d_ff, d_attention_key, d_attention_value, n_heads,
n_attention_chunks,
attention_type=layer_attention_type,
dropout=dropout,
share_qk=(share_qk or issubclass(layer_attention_type,
tl.LSHCausalAttention)),
ff_activation=ff_activation,
ff_use_sru=ff_use_sru,
ff_chunk_size=ff_chunk_size,
mode=mode)
decoder_blocks.append(decoder_block)
return tl.Serial(
concatenate_input_chunks,
tl.ShiftRight(mode=mode),
positional_embedder,
tl.Dup(),
tl.ReversibleSerial(decoder_blocks + [
SplitForOutput(n_sections=n_chunks, axis=-2), # pylint: disable=no-value-for-parameter
]),
Map([
# TODO(kitaev): Test whether dropout should go before or after the
# LayerNorm, and whether dropout broadcasting is needed here.
tl.LayerNorm(),
BroadcastedDropout(rate=dropout, mode=mode), # pylint: disable=no-value-for-parameter
tl.Dense(vocab_size),
tl.LogSoftmax(),
], n_sections=n_chunks),
)
