/
x_transformers.py
755 lines (604 loc) · 24.7 KB
/
x_transformers.py
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import math
import torch
from torch import nn, einsum
import torch.nn.functional as F
from functools import partial
from inspect import isfunction
from collections import namedtuple
from einops import rearrange, repeat, reduce
from entmax import entmax15
from x_transformers.autoregressive_wrapper import AutoregressiveWrapper
# constants
Intermediates = namedtuple('Intermediates', [
'pre_softmax_attn',
'post_softmax_attn'
])
LayerIntermediates = namedtuple('Intermediates', [
'hiddens',
'attn_intermediates'
])
# helpers
def exists(val):
return val is not None
def default(val, d):
if exists(val):
return val
return d() if isfunction(d) else d
def always(val):
def inner(*args, **kwargs):
return val
return inner
def not_equals(val):
def inner(x):
return x != val
return inner
def equals(val):
def inner(x):
return x == val
return inner
def max_neg_value(tensor):
return -torch.finfo(tensor.dtype).max
# keyword argument helpers
def pick_and_pop(keys, d):
values = list(map(lambda key: d.pop(key), keys))
return dict(zip(keys, values))
def group_dict_by_key(cond, d):
return_val = [dict(),dict()]
for key in d.keys():
match = bool(cond(key))
ind = int(not match)
return_val[ind][key] = d[key]
return (*return_val,)
def string_begins_with(prefix, str):
return str.startswith(prefix)
def group_by_key_prefix(prefix, d):
return group_dict_by_key(partial(string_begins_with, prefix), d)
def groupby_prefix_and_trim(prefix, d):
kwargs_with_prefix, kwargs = group_dict_by_key(partial(string_begins_with, prefix), d)
kwargs_without_prefix = dict(map(lambda x: (x[0][len(prefix):], x[1]), tuple(kwargs_with_prefix.items())))
return kwargs_without_prefix, kwargs
# positional embeddings
class AbsolutePositionalEmbedding(nn.Module):
def __init__(self, dim, max_seq_len):
super().__init__()
self.emb = nn.Embedding(max_seq_len, dim)
self.init_()
def init_(self):
nn.init.normal_(self.emb.weight, std = 0.02)
def forward(self, x):
n = torch.arange(x.shape[1], device = x.device)
return self.emb(n)[None, :, :]
class FixedPositionalEmbedding(nn.Module):
def __init__(self, dim):
super().__init__()
inv_freq = 1. / (10000 ** (torch.arange(0, dim, 2).float() / dim))
self.register_buffer('inv_freq', inv_freq)
def forward(self, x, seq_dim = 1, offset = 0):
t = torch.arange(x.shape[seq_dim], device = x.device).type_as(self.inv_freq) + offset
sinusoid_inp = torch.einsum('i , j -> i j', t, self.inv_freq)
emb = torch.cat((sinusoid_inp.sin(), sinusoid_inp.cos()), dim=-1)
return emb[None, :, :]
class RelativePositionBias(nn.Module):
def __init__(self, causal = False, num_buckets = 32, max_distance = 128, heads = 8):
super().__init__()
self.causal = causal
self.num_buckets = num_buckets
self.max_distance = max_distance
self.relative_attention_bias = nn.Embedding(num_buckets, heads)
@staticmethod
def _relative_position_bucket(relative_position, causal = True, num_buckets = 32, max_distance = 128):
ret = 0
n = -relative_position
if not causal:
num_buckets //= 2
ret += (n < 0).long() * num_buckets
n = torch.abs(n)
else:
n = torch.max(n, torch.zeros_like(n))
max_exact = num_buckets // 2
is_small = n < max_exact
val_if_large = max_exact + (
torch.log(n.float() / max_exact) / math.log(max_distance / max_exact) * (num_buckets - max_exact)
).long()
val_if_large = torch.min(val_if_large, torch.full_like(val_if_large, num_buckets - 1))
ret += torch.where(is_small, n, val_if_large)
return ret
def forward(self, qk_dots):
i, j, device = *qk_dots.shape[-2:], qk_dots.device
q_pos = torch.arange(i, dtype = torch.long, device = device)
k_pos = torch.arange(j, dtype = torch.long, device = device)
rel_pos = k_pos[None, :] - q_pos[:, None]
rp_bucket = self._relative_position_bucket(rel_pos, causal = self.causal, num_buckets = self.num_buckets, max_distance = self.max_distance)
values = self.relative_attention_bias(rp_bucket)
bias = rearrange(values, 'i j h -> () h i j')
return qk_dots + bias
# classes
class Scale(nn.Module):
def __init__(self, value, fn):
super().__init__()
self.value = value
self.fn = fn
def forward(self, x, **kwargs):
x, *rest = self.fn(x, **kwargs)
return (x * self.value, *rest)
class Rezero(nn.Module):
def __init__(self, fn):
super().__init__()
self.fn = fn
self.g = nn.Parameter(torch.zeros(1))
def forward(self, x, **kwargs):
x, *rest = self.fn(x, **kwargs)
return (x * self.g, *rest)
class ScaleNorm(nn.Module):
def __init__(self, dim, eps = 1e-5):
super().__init__()
self.scale = dim ** -0.5
self.eps = eps
self.g = nn.Parameter(torch.ones(1))
def forward(self, x):
norm = torch.norm(x, dim = -1, keepdim = True) * self.scale
return x / norm.clamp(min = self.eps) * self.g
class RMSNorm(nn.Module):
def __init__(self, dim, eps = 1e-8):
super().__init__()
self.scale = dim ** -0.5
self.eps = eps
self.g = nn.Parameter(torch.ones(dim))
def forward(self, x):
norm = torch.norm(x, dim = -1, keepdim = True) * self.scale
return x / norm.clamp(min = self.eps) * self.g
class Residual(nn.Module):
def forward(self, x, residual):
return x + residual
class GRUGating(nn.Module):
def __init__(self, dim):
super().__init__()
self.gru = nn.GRUCell(dim, dim)
def forward(self, x, residual):
gated_output = self.gru(
rearrange(x, 'b n d -> (b n) d'),
rearrange(residual, 'b n d -> (b n) d')
)
return gated_output.reshape_as(x)
# feedforward
class GEGLU(nn.Module):
def __init__(self, dim_in, dim_out):
super().__init__()
self.proj = nn.Linear(dim_in, dim_out * 2)
def forward(self, x):
x, gate = self.proj(x).chunk(2, dim = -1)
return x * F.gelu(gate)
class FeedForward(nn.Module):
def __init__(self, dim, dim_out = None, mult = 4, glu = False, dropout = 0.):
super().__init__()
inner_dim = int(dim * mult)
dim_out = default(dim_out, dim)
project_in = nn.Sequential(
nn.Linear(dim, inner_dim),
nn.GELU()
) if not glu else GEGLU(dim, inner_dim)
self.net = nn.Sequential(
project_in,
nn.Dropout(dropout),
nn.Linear(inner_dim, dim_out)
)
def forward(self, x):
return self.net(x)
# attention.
class Attention(nn.Module):
def __init__(
self,
dim,
dim_head = 64,
heads = 8,
causal = False,
mask = None,
talking_heads = False,
sparse_topk = None,
use_entmax15 = False,
num_mem_kv = 0,
dropout = 0.,
on_attn = False
):
super().__init__()
self.scale = dim_head ** -0.5
self.heads = heads
self.causal = causal
self.mask = mask
inner_dim = dim_head * heads
self.to_q = nn.Linear(dim, inner_dim, bias = False)
self.to_k = nn.Linear(dim, inner_dim, bias = False)
self.to_v = nn.Linear(dim, inner_dim, bias = False)
self.dropout = nn.Dropout(dropout)
# talking heads
self.talking_heads = talking_heads
if talking_heads:
self.pre_softmax_proj = nn.Parameter(torch.randn(heads, heads))
self.post_softmax_proj = nn.Parameter(torch.randn(heads, heads))
# explicit topk sparse attention
self.sparse_topk = sparse_topk
# entmax
self.attn_fn = entmax15 if use_entmax15 else F.softmax
# add memory key / values
self.num_mem_kv = num_mem_kv
if num_mem_kv > 0:
self.mem_k = nn.Parameter(torch.randn(heads, num_mem_kv, dim_head))
self.mem_v = nn.Parameter(torch.randn(heads, num_mem_kv, dim_head))
# attention on attention
self.attn_on_attn = on_attn
self.to_out = nn.Sequential(nn.Linear(inner_dim, dim * 2), nn.GLU()) if on_attn else nn.Linear(inner_dim, dim)
def forward(
self,
x,
context = None,
mask = None,
context_mask = None,
rel_pos = None,
sinusoidal_emb = None,
prev_attn = None,
mem = None
):
b, n, _, h, talking_heads, device = *x.shape, self.heads, self.talking_heads, x.device
kv_input = default(context, x)
q_input = x
k_input = kv_input
v_input = kv_input
if exists(mem):
k_input = torch.cat((mem, k_input), dim = -2)
v_input = torch.cat((mem, v_input), dim = -2)
if exists(sinusoidal_emb):
# in shortformer, the query would start at a position offset depending on the past cached memory
offset = k_input.shape[-2] - q_input.shape[-2]
q_input = q_input + sinusoidal_emb(q_input, offset = offset)
k_input = k_input + sinusoidal_emb(k_input)
q = self.to_q(q_input)
k = self.to_k(k_input)
v = self.to_v(v_input)
q, k, v = map(lambda t: rearrange(t, 'b n (h d) -> b h n d', h = h), (q, k, v))
input_mask = None
if any(map(exists, (mask, context_mask))):
q_mask = default(mask, lambda: torch.ones((b, n), device = device).bool())
k_mask = q_mask if not exists(context) else context_mask
k_mask = default(k_mask, lambda: torch.ones((b, k.shape[-2]), device = device).bool())
q_mask = rearrange(q_mask, 'b i -> b () i ()')
k_mask = rearrange(k_mask, 'b j -> b () () j')
input_mask = q_mask * k_mask
if self.num_mem_kv > 0:
mem_k, mem_v = map(lambda t: repeat(t, 'h n d -> b h n d', b = b), (self.mem_k, self.mem_v))
k = torch.cat((mem_k, k), dim = -2)
v = torch.cat((mem_v, v), dim = -2)
if exists(input_mask):
input_mask = F.pad(input_mask, (self.num_mem_kv, 0), value = True)
dots = einsum('b h i d, b h j d -> b h i j', q, k) * self.scale
mask_value = max_neg_value(dots)
if exists(prev_attn):
dots = dots + prev_attn
pre_softmax_attn = dots
if talking_heads:
dots = einsum('b h i j, h k -> b k i j', dots, self.pre_softmax_proj).contiguous()
if exists(rel_pos):
dots = rel_pos(dots)
if exists(input_mask):
dots.masked_fill_(~input_mask, mask_value)
del input_mask
if self.causal:
i, j = dots.shape[-2:]
mask = torch.ones((i, j), device = device).triu_(j - i + 1).bool()
dots.masked_fill_(mask, mask_value)
del mask
if exists(self.sparse_topk) and self.sparse_topk < dots.shape[-1]:
top, _ = dots.topk(self.sparse_topk, dim = -1)
vk = top[..., -1].unsqueeze(-1).expand_as(dots)
mask = dots < vk
dots.masked_fill_(mask, mask_value)
del mask
attn = self.attn_fn(dots, dim = -1)
post_softmax_attn = attn
attn = self.dropout(attn)
if talking_heads:
attn = einsum('b h i j, h k -> b k i j', attn, self.post_softmax_proj).contiguous()
out = einsum('b h i j, b h j d -> b h i d', attn, v)
out = rearrange(out, 'b h n d -> b n (h d)')
intermediates = Intermediates(
pre_softmax_attn = pre_softmax_attn,
post_softmax_attn = post_softmax_attn
)
return self.to_out(out), intermediates
class AttentionLayers(nn.Module):
def __init__(
self,
dim,
depth,
heads = 8,
causal = False,
cross_attend = False,
only_cross = False,
use_scalenorm = False,
use_rmsnorm = False,
use_rezero = False,
rel_pos_bias = False,
rel_pos_num_buckets = 32,
rel_pos_max_distance = 128,
position_infused_attn = False,
custom_layers = None,
sandwich_coef = None,
par_ratio = None,
residual_attn = False,
cross_residual_attn = False,
macaron = False,
pre_norm = True,
gate_residual = False,
**kwargs
):
super().__init__()
self.dim = dim
self.depth = depth
self.layers = nn.ModuleList([])
self.has_pos_emb = position_infused_attn or rel_pos_bias
self.pia_pos_emb = FixedPositionalEmbedding(dim) if position_infused_attn else None
assert rel_pos_num_buckets <= rel_pos_max_distance, 'number of relative position buckets must be less than the relative position max distance'
self.rel_pos = RelativePositionBias(causal = causal, heads = heads, num_buckets = rel_pos_num_buckets, max_distance = rel_pos_max_distance) if rel_pos_bias else None
self.pre_norm = pre_norm and not residual_attn
self.residual_attn = residual_attn
self.cross_residual_attn = cross_residual_attn
norm_class = ScaleNorm if use_scalenorm else nn.LayerNorm
norm_class = RMSNorm if use_rmsnorm else norm_class
norm_fn = partial(norm_class, dim)
norm_fn = nn.Identity if use_rezero else norm_fn
branch_fn = Rezero if use_rezero else None
ff_kwargs, kwargs = groupby_prefix_and_trim('ff_', kwargs)
attn_kwargs, _ = groupby_prefix_and_trim('attn_', kwargs)
if cross_attend and not only_cross:
default_block = ('a', 'c', 'f')
elif cross_attend and only_cross:
default_block = ('c', 'f')
else:
default_block = ('a', 'f')
if macaron:
default_block = ('f',) + default_block
if exists(custom_layers):
layer_types = custom_layers
elif exists(par_ratio):
par_depth = depth * len(default_block)
assert 1 < par_ratio <= par_depth, 'par ratio out of range'
default_block = tuple(filter(not_equals('f'), default_block))
par_attn = par_depth // par_ratio
depth_cut = par_depth * 2 // 3 # 2 / 3 attention layer cutoff suggested by PAR paper
par_width = (depth_cut + depth_cut // par_attn) // par_attn
assert len(default_block) <= par_width, 'default block is too large for par_ratio'
par_block = default_block + ('f',) * (par_width - len(default_block))
par_head = par_block * par_attn
layer_types = par_head + ('f',) * (par_depth - len(par_head))
elif exists(sandwich_coef):
assert sandwich_coef > 0 and sandwich_coef <= depth, 'sandwich coefficient should be less than the depth'
layer_types = ('a',) * sandwich_coef + default_block * (depth - sandwich_coef) + ('f',) * sandwich_coef
else:
layer_types = default_block * depth
self.layer_types = layer_types
self.num_attn_layers = len(list(filter(equals('a'), layer_types)))
for layer_type in self.layer_types:
if layer_type == 'a':
layer = Attention(dim, heads = heads, causal = causal, **attn_kwargs)
elif layer_type == 'c':
layer = Attention(dim, heads = heads, **attn_kwargs)
elif layer_type == 'f':
layer = FeedForward(dim, **ff_kwargs)
layer = layer if not macaron else Scale(0.5, layer)
else:
raise Exception(f'invalid layer type {layer_type}')
if isinstance(layer, Attention) and exists(branch_fn):
layer = branch_fn(layer)
if gate_residual:
residual_fn = GRUGating(dim)
else:
residual_fn = Residual()
self.layers.append(nn.ModuleList([
norm_fn(),
layer,
residual_fn
]))
def forward(
self,
x,
context = None,
mask = None,
context_mask = None,
mems = None,
return_hiddens = False
):
hiddens = []
intermediates = []
prev_attn = None
prev_cross_attn = None
mems = mems.copy() if exists(mems) else [None] * self.num_attn_layers
for ind, (layer_type, (norm, block, residual_fn)) in enumerate(zip(self.layer_types, self.layers)):
is_last = ind == (len(self.layers) - 1)
if layer_type == 'a':
hiddens.append(x)
layer_mem = mems.pop(0)
residual = x
if self.pre_norm:
x = norm(x)
if layer_type == 'a':
out, inter = block(x, mask = mask, sinusoidal_emb = self.pia_pos_emb, rel_pos = self.rel_pos, prev_attn = prev_attn, mem = layer_mem)
elif layer_type == 'c':
out, inter = block(x, context = context, mask = mask, context_mask = context_mask, prev_attn = prev_cross_attn)
elif layer_type == 'f':
out = block(x)
x = residual_fn(out, residual)
if layer_type in ('a', 'c'):
intermediates.append(inter)
if layer_type == 'a' and self.residual_attn:
prev_attn = inter.pre_softmax_attn
elif layer_type == 'c' and self.cross_residual_attn:
prev_cross_attn = inter.pre_softmax_attn
if not self.pre_norm and not is_last:
x = norm(x)
if return_hiddens:
intermediates = LayerIntermediates(
hiddens = hiddens,
attn_intermediates = intermediates
)
return x, intermediates
return x
class Encoder(AttentionLayers):
def __init__(self, **kwargs):
assert 'causal' not in kwargs, 'cannot set causality on encoder'
super().__init__(causal = False, **kwargs)
class Decoder(AttentionLayers):
def __init__(self, **kwargs):
assert 'causal' not in kwargs, 'cannot set causality on decoder'
super().__init__(causal = True, **kwargs)
class CrossAttender(AttentionLayers):
def __init__(self, **kwargs):
super().__init__(cross_attend = True, only_cross = True, **kwargs)
class ViTransformerWrapper(nn.Module):
def __init__(
self,
*,
image_size,
patch_size,
attn_layers,
num_classes = None,
dropout = 0.,
emb_dropout = 0.
):
super().__init__()
assert isinstance(attn_layers, Encoder), 'attention layers must be an Encoder'
assert image_size % patch_size == 0, 'image dimensions must be divisible by the patch size'
dim = attn_layers.dim
num_patches = (image_size // patch_size) ** 2
patch_dim = 3 * patch_size ** 2
self.patch_size = patch_size
self.pos_embedding = nn.Parameter(torch.randn(1, num_patches + 1, dim))
self.patch_to_embedding = nn.Linear(patch_dim, dim)
self.cls_token = nn.Parameter(torch.randn(1, 1, dim))
self.dropout = nn.Dropout(emb_dropout)
self.attn_layers = attn_layers
self.norm = nn.LayerNorm(dim)
self.mlp_head = FeedForward(dim, dim_out = num_classes, dropout = dropout) if exists(num_classes) else None
def forward(
self,
img,
return_embeddings = False
):
p = self.patch_size
x = rearrange(img, 'b c (h p1) (w p2) -> b (h w) (p1 p2 c)', p1 = p, p2 = p)
x = self.patch_to_embedding(x)
b, n, _ = x.shape
cls_tokens = repeat(self.cls_token, '() n d -> b n d', b = b)
x = torch.cat((cls_tokens, x), dim=1)
x += self.pos_embedding[:, :(n + 1)]
x = self.dropout(x)
x = self.attn_layers(x)
x = self.norm(x)
if not exists(self.mlp_head) or return_embeddings:
return x
return self.mlp_head(x[:, 0])
class TransformerWrapper(nn.Module):
def __init__(
self,
*,
num_tokens,
max_seq_len,
attn_layers,
emb_dim = None,
max_mem_len = 0.,
emb_dropout = 0.,
num_memory_tokens = None,
tie_embedding = False,
use_pos_emb = True
):
super().__init__()
assert isinstance(attn_layers, AttentionLayers), 'attention layers must be one of Encoder or Decoder'
dim = attn_layers.dim
emb_dim = default(emb_dim, dim)
self.max_seq_len = max_seq_len
self.max_mem_len = max_mem_len
self.token_emb = nn.Embedding(num_tokens, emb_dim)
self.pos_emb = AbsolutePositionalEmbedding(emb_dim, max_seq_len) if (use_pos_emb and not attn_layers.has_pos_emb) else always(0)
self.emb_dropout = nn.Dropout(emb_dropout)
self.project_emb = nn.Linear(emb_dim, dim) if emb_dim != dim else nn.Identity()
self.attn_layers = attn_layers
self.norm = nn.LayerNorm(dim)
self.init_()
self.to_logits = nn.Linear(dim, num_tokens) if not tie_embedding else lambda t: t @ self.token_emb.weight.t()
# memory tokens (like [cls]) from Memory Transformers paper
num_memory_tokens = default(num_memory_tokens, 0)
self.num_memory_tokens = num_memory_tokens
if num_memory_tokens > 0:
self.memory_tokens = nn.Parameter(torch.randn(num_memory_tokens, dim))
# let funnel encoder know number of memory tokens, if specified
# TODO: think of a cleaner solution
if hasattr(attn_layers, 'num_memory_tokens'):
attn_layers.num_memory_tokens = num_memory_tokens
def init_(self):
nn.init.normal_(self.token_emb.weight, std = 0.02)
def forward(
self,
x,
return_embeddings = False,
mask = None,
return_mems = False,
return_attn = False,
mems = None,
**kwargs
):
b, n, device, num_mem = *x.shape, x.device, self.num_memory_tokens
x = self.token_emb(x)
x += self.pos_emb(x)
x = self.emb_dropout(x)
x = self.project_emb(x)
if num_mem > 0:
mem = repeat(self.memory_tokens, 'n d -> b n d', b = b)
x = torch.cat((mem, x), dim = 1)
# auto-handle masking after appending memory tokens
if exists(mask):
mask = F.pad(mask, (num_mem, 0), value = True)
x, intermediates = self.attn_layers(x, mask = mask, mems = mems, return_hiddens = True, **kwargs)
x = self.norm(x)
mem, x = x[:, :num_mem], x[:, num_mem:]
out = self.to_logits(x) if not return_embeddings else x
if return_mems:
hiddens = intermediates.hiddens
new_mems = list(map(lambda pair: torch.cat(pair, dim = -2), zip(mems, hiddens))) if exists(mems) else hiddens
new_mems = list(map(lambda t: t[..., -self.max_mem_len:, :].detach(), new_mems))
return out, new_mems
if return_attn:
attn_maps = list(map(lambda t: t.post_softmax_attn, intermediates.attn_intermediates))
return out, attn_maps
return out
class XTransformer(nn.Module):
def __init__(
self,
*,
dim,
tie_token_emb = False,
**kwargs
):
super().__init__()
enc_kwargs, kwargs = groupby_prefix_and_trim('enc_', kwargs)
dec_kwargs, kwargs = groupby_prefix_and_trim('dec_', kwargs)
assert 'dim' not in enc_kwargs and 'dim' not in dec_kwargs, 'dimension of either encoder or decoder must be set with `dim` keyword'
enc_transformer_kwargs = pick_and_pop(['num_tokens', 'max_seq_len'], enc_kwargs)
enc_transformer_kwargs['num_memory_tokens'] = enc_kwargs.pop('num_memory_tokens', None)
dec_transformer_kwargs = pick_and_pop(['num_tokens', 'max_seq_len'], dec_kwargs)
self.encoder = TransformerWrapper(
**enc_transformer_kwargs,
attn_layers = Encoder(dim = dim, **enc_kwargs)
)
self.decoder = TransformerWrapper(
**dec_transformer_kwargs,
attn_layers = Decoder(dim = dim, cross_attend = True, **dec_kwargs)
)
if tie_token_emb:
self.decoder.token_emb = self.encoder.token_emb
self.decoder = AutoregressiveWrapper(self.decoder)
@torch.no_grad()
def generate(self, seq_in, seq_out_start, seq_len, src_mask = None):
encodings = self.encoder(seq_in, return_embeddings = True, mask = src_mask)
return self.decoder.generate(seq_out_start, seq_len, context = encodings, context_mask = src_mask)
def forward(self, src, tgt, src_mask = None, tgt_mask = None):
enc = self.encoder(src, mask = src_mask, return_embeddings = True)
out = self.decoder(tgt, context = enc, mask = tgt_mask, context_mask = src_mask)
return out