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#===================================================================================================================
#
# X Trasformer Python Module
#
# Partial x-transformers code With useful modifications as a stand-alone Python module
#
# Version 1.0
#
# Original source code courtesy of lucidrains
# https://github.com/lucidrains/x-transformers
#
# Original source code retrieved on 04/30/2025
# Original version 2.3.1 / Commit 458bc12
#
# Project Los Angeles
# Tegridy Code 2025
#
#===================================================================================================================
#
# Critical dependencies
#
# !pip install torch
# !pip install einops
# !pip install einx
#
#===================================================================================================================
from __future__ import annotations
import os
os.environ['USE_FLASH_ATTENTION'] = '1'
import torch
from torch.nn.attention import SDPBackend, sdpa_kernel
torch.backends.cuda.enable_flash_sdp(True)
#==================================================================================================================================
# attend.py
#==================================================================================================================================
from functools import partial
from typing import Tuple, Callable
import torch
from torch.nn import Module
from torch import nn, einsum, Tensor
import torch.nn.functional as F
from collections import namedtuple
from functools import wraps
from packaging import version
from dataclasses import dataclass
from einops import rearrange, repeat, pack, unpack
#========================================================================================================================
# constants
@dataclass
class Intermediates:
qk_similarities: Tensor | None = None
pre_softmax_attn: Tensor | None = None
post_softmax_attn: Tensor | None = None
values: Tensor | None = None
cached_kv: Tuple[Tensor, Tensor] | None = None
layer_type: str | None = None
def to_tuple(self):
return (self.qk_similarities, self.pre_softmax_attn, self.post_softmax_attn)
# helpers
def exists(val):
return val is not None
def default(val, d):
return val if exists(val) else d
def at_most_one_of(*bools):
return sum([*map(int, bools)]) <= 1
def compact(arr):
return [*filter(exists, arr)]
@torch.jit.script
def softclamp(t: Tensor, value: float):
return (t / value).tanh() * value
def pack_one(t, pattern):
return pack([t], pattern)
def unpack_one(t, ps, pattern):
return unpack(t, ps, pattern)[0]
def once(fn):
called = False
@wraps(fn)
def inner(x):
nonlocal called
if called:
return
called = True
return fn(x)
return inner
print_once = once(print)
# selective attention
# https://arxiv.org/abs/2410.02703 - section 3.3
# it is a technique to allow each token to prevent itself from being attended to by future tokens
# if sim_head_gate not supplied, will use the first head of the attention logits (sim in this framework)
def selective_attn(
sim,
sim_head_gate = None,
no_mask_sos = True
):
i, j, device = *sim.shape[-2:], sim.device
sim_head_gate = default(sim_head_gate, sim[:, 0])
gate = F.relu(sim_head_gate) # only positive
if no_mask_sos:
gate = gate.clone()
gate[..., -i] = 0.
eye = torch.eye(i, device = device)
if j > i:
eye = F.pad(eye, (j - i, 0), value = 1.)
gate = (1. - eye) * gate
gate = F.pad(gate, (0, 0, 1, -1), value = 0.) # only allow for masking the future
gate = gate.cumsum(dim = -2)
return sim - rearrange(gate, 'b i j -> b 1 i j')
# alternative distance functions
def qk_l2_dist_squared(q, k):
if k.ndim == 3:
k = repeat(k, 'b j d -> b h j d', h = q.shape[1])
q, packed_shape = pack_one(q, '* i d')
k, _ = pack_one(k, '* j d')
l2_dist_squared = torch.cdist(q, k) ** 2
return unpack_one(l2_dist_squared, packed_shape, '* i j')
# one-hot straight through softmax
def one_hot_straight_through(logits, temperature = 1.):
one_hot_indices = logits.argmax(dim = -1, keepdim = True)
one_hot = torch.zeros_like(logits).scatter(-1, one_hot_indices, 1.)
soft_attn = (logits / temperature).softmax(dim = -1)
return one_hot + soft_attn - soft_attn.detach()
# sparse topk attention - only keep topk attn logits for softmax
# optional straight through with masked out logits by setting `attn_sparse_topk_straight_through = True`
def sparse_topk_attn(
logits,
sparse_topk,
temperature = 1.,
straight_through = False
):
orig_logits = logits
mask_value = -torch.finfo(logits.dtype).max
top_values, _ = logits.topk(sparse_topk, dim = -1)
sparse_topk_mask = (logits >= top_values[..., -1:]) & (logits > mask_value)
logits = logits.masked_fill(~sparse_topk_mask, mask_value)
topk_attn = logits.softmax(dim = -1)
if not straight_through:
return topk_attn
soft_attn = (orig_logits / temperature).softmax(dim = -1)
return topk_attn.detach() + soft_attn - soft_attn.detach()
# functions for creating causal mask
# need a special one for onnx cpu (no support for .triu)
def create_causal_mask(i, j, device):
return torch.ones((i, j), device = device, dtype = torch.bool).triu(j - i + 1)
def onnx_create_causal_mask(i, j, device):
r = torch.arange(i, device = device)
causal_mask = rearrange(r, 'i -> i 1') < rearrange(r, 'j -> 1 j')
causal_mask = F.pad(causal_mask, (j - i, 0), value = False)
return causal_mask
# main class
class Attend(Module):
def __init__(
self,
*,
dropout = 0.,
causal = False,
heads = None,
pre_talking_heads = False,
post_talking_heads = False,
pre_scale_post_talking_heads = False,
sparse_topk = None,
sparse_topk_straight_through = False,
scale = None,
qk_norm = False,
l2_distance = False,
sigmoid = False,
custom_attn_fn: Callable | None = None,
flash = False,
softclamp_logits = False,
logit_softclamp_value = 50.,
add_zero_kv = False,
selective = False,
hard = False,
cope = None,
onnxable = False,
sdp_kwargs: dict = dict(
enable_flash = True,
enable_math = True,
enable_mem_efficient = True
)
):
super().__init__()
self.scale = scale
# causal related
self.causal = causal
self.create_causal_mask = onnx_create_causal_mask if onnxable else create_causal_mask
# attention type
is_sparse_topk_attn = exists(sparse_topk)
assert not (flash and sigmoid), 'sigmoid attention not available for flash'
assert not (flash and hard), 'hard attention not available for flash'
assert not (flash and is_sparse_topk_attn), 'topk attention not available for flash'
assert at_most_one_of(sigmoid, hard, l2_distance, is_sparse_topk_attn)
if exists(custom_attn_fn):
self.attn_fn = custom_attn_fn
elif sigmoid:
self.attn_fn = F.sigmoid
elif hard:
self.attn_fn = one_hot_straight_through
elif is_sparse_topk_attn:
self.attn_fn = partial(sparse_topk_attn, sparse_topk = sparse_topk, straight_through = sparse_topk_straight_through)
else:
softmax_fn = partial(F.softmax, dim = -1)
self.attn_fn = partial(softmax_fn, dtype = torch.float32) if not qk_norm else softmax_fn
# dropouts
self.dropout = dropout
self.attn_dropout = nn.Dropout(dropout)
# talking heads
assert not (flash and (pre_talking_heads or post_talking_heads or pre_scale_post_talking_heads)), 'talking heads not compatible with flash attention'
self.pre_softmax_talking_heads = nn.Conv2d(heads, heads, 1, bias = False) if pre_talking_heads else None
self.post_softmax_talking_heads = nn.Conv2d(heads, heads, 1, bias = False) if post_talking_heads else None
self.pre_scale_post_talking_heads = nn.Conv2d(heads, heads, 1, bias = False) if pre_scale_post_talking_heads else None
if exists(self.pre_softmax_talking_heads):
nn.init.dirac_(self.pre_softmax_talking_heads.weight)
if exists(self.post_softmax_talking_heads):
nn.init.dirac_(self.post_softmax_talking_heads.weight)
if exists(self.pre_scale_post_talking_heads):
# an improvisation where heads are combined pre-softmax attention, then used to scale post-softmax attention
nn.init.dirac_(self.pre_scale_post_talking_heads.weight)
# selective attention
assert not (flash and selective), 'selective attention cannot work on flash attention'
assert not (selective and not causal), 'selective attention is designed for autoregressive'
self.selective = selective
# l2 distance attention
self.l2_distance = l2_distance
# add a key / value token composed of zeros
# in case this helps controlling outliers, proposed by https://www.evanmiller.org/attention-is-off-by-one.html
self.add_zero_kv = add_zero_kv
# soft clamp attention logit value
if softclamp_logits:
assert not flash, 'flash attention not compatible with logit softclamp value yet'
assert logit_softclamp_value > 0.
self.softclamp_logits = softclamp_logits
self.logit_softclamp_value = logit_softclamp_value
# contextual positional encoding
self.cope = cope
# flash attention
self.flash = flash
torch_version = version.parse(torch.__version__)
assert not (flash and torch_version < version.parse('2.0.0')), 'in order to use flash attention, you must be using pytorch 2.0 or above'
# torch 2.3 uses new backend and context manager
if torch_version >= version.parse('2.3'):
from torch.nn.attention import SDPBackend
str_to_backend = dict(
enable_flash = SDPBackend.FLASH_ATTENTION,
enable_mem_efficient = SDPBackend.EFFICIENT_ATTENTION,
enable_math = SDPBackend.MATH,
enable_cudnn = SDPBackend.CUDNN_ATTENTION
)
sdpa_backends = [str_to_backend[enable_str] for enable_str, enable in sdp_kwargs.items() if enable]
self.sdp_context_manager = partial(torch.nn.attention.sdpa_kernel, sdpa_backends)
else:
self.sdp_context_manager = partial(torch.backends.cuda.sdp_kernel, **sdp_kwargs)
def flash_attn(
self,
q, k, v,
mask = None,
attn_bias = None
):
batch, heads, q_len, _, k_len, is_cuda, device = *q.shape, k.shape[-2], q.is_cuda, q.device
# Recommended for multi-query single-key-value attention by Tri Dao
# kv shape torch.Size([1, 512, 64]) -> torch.Size([1, 8, 512, 64])
if k.ndim == 3:
k = repeat(k, 'b ... -> b h ...', h = q.shape[1])
if v.ndim == 3:
v = repeat(v, 'b ... -> b h ...', h = q.shape[1])
# handle maybe l2 distance
if self.l2_distance:
k_norm_sq = k.norm(dim = -1, keepdim = True) ** 2
k = F.pad(k, (0, 1), value = -1.)
k = torch.cat((k, k_norm_sq), dim = -1)
q_norm_sq = q.norm(dim = -1, keepdim = True) ** 2
q = torch.cat((2 * q, q_norm_sq), dim = -1)
q = F.pad(q, (0, 1), value = -1.)
# handle scale - by default they scale by dim_head ** -0.5, but need to take care if using cosine sim attention
if exists(self.scale):
default_scale = q.shape[-1] ** -0.5
q = q * (self.scale / default_scale)
# Check if mask exists and expand to compatible shape
# The mask is B L, so it would have to be expanded to B H N L
causal = self.causal
# in the case of kv caching with one token (q_len == 1), just turn off causal masking
# in speculative decoding, this may go up to 5-6, so right aligned causal mask will be needed there
if q_len == 1 and causal:
causal = False
# expand key padding mask
if exists(mask):
assert mask.ndim == 4
mask = mask.expand(batch, heads, q_len, k_len)
# handle kv cache - this should be bypassable in updated flash attention 2
if k_len > q_len and causal:
causal_mask = self.create_causal_mask(q_len, k_len, device = device)
if not exists(mask):
mask = ~causal_mask
else:
mask = mask & ~causal_mask
causal = False
# manually handle causal mask, if another mask was given
if exists(mask) and causal:
causal_mask = self.create_causal_mask(q_len, k_len, device = device)
mask = mask & ~causal_mask
causal = False
# protect against an entire row being masked out
row_is_entirely_masked = None
if exists(mask):
row_is_entirely_masked = ~mask.any(dim = -1)
# handle alibi positional bias
# convert from bool to float
if exists(attn_bias):
attn_bias = attn_bias.expand(batch, heads, -1, -1)
# if mask given, the mask would already contain the causal mask from above logic
# otherwise, if no mask given but still causal, mask out alibi positional bias to a large negative number
mask_value = -torch.finfo(q.dtype).max
if exists(mask):
attn_bias = attn_bias.masked_fill(~mask, mask_value // 2)
elif causal:
causal_mask = self.create_causal_mask(q_len, k_len, device = device)
attn_bias = attn_bias.masked_fill(causal_mask, mask_value // 2)
causal = False
# scaled_dot_product_attention handles attn_mask either as bool or additive bias
# make it an additive bias here
mask = attn_bias
# pytorch 2.0 flash attn: q, k, v, mask, dropout, causal, softmax_scale
with self.sdp_context_manager():
out = F.scaled_dot_product_attention(
q, k, v,
attn_mask = mask,
dropout_p = self.dropout if self.training else 0.,
is_causal = causal
)
# for a row that is entirely masked out, should zero out the output of that row token
if exists(row_is_entirely_masked) and row_is_entirely_masked.any():
out = out.masked_fill(row_is_entirely_masked[..., None], 0.)
return out, Intermediates()
def forward(
self,
q, k, v,
mask = None,
attn_bias = None,
prev_attn = None
):
"""
einstein notation
b - batch
h - heads
n, i, j - sequence length (base sequence length, source, target)
d - feature dimension
"""
n, heads, kv_heads, device = q.shape[-2], q.shape[1], k.shape[1], q.device
scale = default(self.scale, q.shape[-1] ** -0.5)
causal = self.causal
# handle key padding mask
if exists(mask) and mask.ndim == 2:
mask = rearrange(mask, 'b j -> b 1 1 j')
# handle kv cached decoding
if n == 1 and causal:
causal = False
# handle grouped multi-query attention
if kv_heads == 1:
k, v = tuple(rearrange(t, 'b 1 n d -> b n d') for t in (k, v))
elif kv_heads < heads:
k, v = tuple(repeat(t, 'b kvh n d -> b (r kvh) n d', r = heads // kv_heads) for t in (k, v))
# handle zero kv, as means for allowing network to attend to nothing
if self.add_zero_kv:
k, v = tuple(F.pad(t, (0, 0, 1, 0), value = 0.) for t in (k, v))
if exists(mask):
mask = F.pad(mask, (1, 0), value = True)
if exists(attn_bias):
attn_bias = F.pad(attn_bias, (1, 0), value = 0.)
if self.flash:
assert not exists(prev_attn), 'residual attention not compatible with flash attention'
return self.flash_attn(q, k, v, mask = mask, attn_bias = attn_bias)
kv_einsum_eq = 'b j d' if k.ndim == 3 else 'b h j d'
if not self.l2_distance:
sim = einsum(f'b h i d, {kv_einsum_eq} -> b h i j', q, k)
else:
sim = -qk_l2_dist_squared(q, k)
sim = sim * scale
if exists(prev_attn):
sim = sim + prev_attn
qk_similarities = sim.clone()
if exists(self.pre_scale_post_talking_heads):
pre_to_post_scale = self.pre_scale_post_talking_heads(sim)
if exists(self.pre_softmax_talking_heads):
sim = sim + self.pre_softmax_talking_heads(sim)
if exists(attn_bias):
sim = sim + attn_bias
if self.softclamp_logits:
sim = softclamp(sim, self.logit_softclamp_value)
i, j, dtype = *sim.shape[-2:], sim.dtype
mask_value = -torch.finfo(sim.dtype).max
if exists(mask):
sim = sim.masked_fill(~mask, mask_value)
if causal:
causal_mask = self.create_causal_mask(i, j, device = device)
sim = sim.masked_fill(causal_mask, mask_value)
row_is_entirely_masked = None
if exists(mask):
row_is_entirely_masked = ~mask.any(dim = -1)
if exists(self.cope):
sim = sim + self.cope(q, sim)
if self.selective:
sim = selective_attn(sim)
pre_softmax_attn = sim
attn = self.attn_fn(sim)
attn = attn.type(dtype)
post_softmax_attn = attn
attn = self.attn_dropout(attn)
if exists(self.post_softmax_talking_heads):
attn = self.post_softmax_talking_heads(attn)
if exists(self.pre_scale_post_talking_heads):
attn = attn * pre_to_post_scale
out = einsum(f'b h i j, {kv_einsum_eq} -> b h i d', attn, v)
intermediates = Intermediates(
qk_similarities = qk_similarities,
pre_softmax_attn = pre_softmax_attn,
post_softmax_attn = post_softmax_attn
)
if exists(row_is_entirely_masked) and row_is_entirely_masked.any():
out = out.masked_fill(row_is_entirely_masked[..., None], 0.)
return out, intermediates
#=================================================================================================================================
# x_transformers.py
#=================================================================================================================================
from typing import Callable
import math
from copy import deepcopy
from random import random, randrange
from packaging import version
import torch
from torch.amp import autocast
import torch.nn.functional as F
from torch import nn, einsum, tensor, Tensor, cat, stack, arange, is_tensor
from torch.utils._pytree import tree_flatten, tree_unflatten
from torch.nn import Module, ModuleList, ModuleDict
from functools import partial, wraps
from collections import namedtuple
from contextlib import nullcontext
from dataclasses import dataclass
import einx
from einops.layers.torch import Rearrange
from einops import rearrange, repeat, reduce, pack, unpack
# einstein notation
# b - batch
# n - sequence
# d - feature dimension
# h - attention heads
# i, j - sequence (source, target)
# constants
DEFAULT_DIM_HEAD = 64
@dataclass
class LayerIntermediates:
hiddens: list[Tensor] | None = None # all hiddens, before the final norm (in pre-norm architecture)
last_hidden: Tensor | None = None # very last hidden after all attention layers, after the final norm
attn_intermediates: list[Intermediates] | None = None
layer_hiddens: list[Tensor] | None = None
attn_z_loss: Tensor | None = None
mems: Tensor | None = None
memory_tokens: Tensor | None = None
logit_entropies: Tensor | None = None
LinearNoBias = partial(nn.Linear, bias = False)
# helpers
def exists(val):
return val is not None
def default(val, d):
if exists(val):
return val
return d() if callable(d) else d
def identity(t, *args, **kwargs):
return t
def first(it, default = None):
return it[0] if len(it) > 0 else default
def is_empty(x):
return len(x) == 0
def cast_tuple(val, depth = 1):
return val if isinstance(val, tuple) else (val,) * depth
def divisible_by(num, den):
return (num % den) == 0
def maybe(fn = None):
if not exists(fn):
fn = identity
@wraps(fn)
def inner(x, *args, **kwargs):
if not exists(x):
return x
return fn(x, *args, **kwargs)
return inner
def at_most_one_of(*bools):
return sum(map(int, bools)) <= 1
class always():
def __init__(self, val):
self.val = val
def __call__(self, *args, **kwargs):
return self.val
class not_equals():
def __init__(self, val):
self.val = val
def __call__(self, x, *args, **kwargs):
return x != self.val
class equals():
def __init__(self, val):
self.val = val
def __call__(self, x, *args, **kwargs):
return x == self.val
def Sequential(*modules):
return nn.Sequential(*filter(exists, modules))
# tensor helpers
def log(t, eps = 1e-20):
return t.clamp(min = eps).log()
def max_neg_value(tensor):
return -torch.finfo(tensor.dtype).max
def l2norm(t, groups = 1):
t = rearrange(t, '... (g d) -> ... g d', g = groups)
t = F.normalize(t, p = 2, dim = -1)
return rearrange(t, '... g d -> ... (g d)')
def softclamp(t, value):
return (t / value).tanh() * value
def masked_mean(t, mask = None, dim = 1):
if not exists(mask):
return t.mean(dim = dim)
dims_append = (1,) * (t.ndim - mask.ndim)
mask = mask.reshape(*mask.shape, *dims_append)
num = (t * mask).sum(dim = dim)
den = mask.sum(dim = dim).clamp(min = 1.)
return num / den
def pad_at_dim(t, pad: tuple[int, int], dim = -1, value = 0.):
if pad == (0, 0):
return t
dims_from_right = (- dim - 1) if dim < 0 else (t.ndim - dim - 1)
zeros = ((0, 0) * dims_from_right)
return F.pad(t, (*zeros, *pad), value = value)
def or_reduce(masks):
head, *body = masks
for rest in body:
head = head | rest
return head
# entropy
def calc_entropy(
t: Tensor,
is_prob = False
):
prob = t.softmax(dim = -1) if not is_prob else t
return -(prob * log(prob)).sum(dim = -1)
# auxiliary loss helpers
def calc_z_loss(
pre_softmax_attns: list[Tensor],
mask = None,
weight = 1.
):
# the same loss applied to the mixture of experts router logits in https://arxiv.org/abs/2202.08906
# in the paper, in a tiny footnote, they mention using it on attention logits with stabilizing effects
# also used in PaLM as one of the measures
lse = 0.
for attn in pre_softmax_attns:
lse = lse + attn.logsumexp(dim = -1)
loss = torch.square(lse)
loss = reduce(loss, 'b h n -> b n', 'sum')
if not exists(mask):
return loss.mean() * weight
loss = loss[mask].sum() / mask.sum().clamp(min = 1e-5)
return loss * weight
# init helpers
def init_zero_(layer):
nn.init.constant_(layer.weight, 0.)
if exists(layer.bias):
nn.init.constant_(layer.bias, 0.)
# keyword argument helpers
def pick_and_pop(keys, d):
values = tuple(d.pop(key) for key in 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 tuple(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)
prefix_len = len(prefix)
kwargs_without_prefix = {key[prefix_len:]: value for key, value in kwargs_with_prefix.items()}
return kwargs_without_prefix, kwargs
# structured dropout, more effective than traditional attention dropouts
def dropout_seq(seq, mask, dropout):
b, n, *_, device = *seq.shape, seq.device
logits = torch.randn(b, n, device = device)
if exists(mask):
mask_value = max_neg_value(logits)
logits = logits.masked_fill(~mask, mask_value)
keep_prob = 1. - dropout
num_keep = max(1, int(keep_prob * n))
keep_indices = logits.topk(num_keep, dim = 1).indices
batch_indices = arange(b, device = device)
batch_indices = rearrange(batch_indices, 'b -> b 1')
seq = seq[batch_indices, keep_indices]
if exists(mask):
seq_counts = mask.sum(dim = -1)
seq_keep_counts = torch.ceil(seq_counts * keep_prob).int()
keep_mask = arange(num_keep, device = device) < rearrange(seq_keep_counts, 'b -> b 1')
mask = mask[batch_indices, keep_indices] & keep_mask
return seq, mask
# activations
class ReluSquared(Module):
def forward(self, x):
return F.relu(x) ** 2
# embedding
class TokenEmbedding(Module):
def __init__(self, dim, num_tokens, l2norm_embed = False):
super().__init__()
self.l2norm_embed = l2norm_embed
self.emb = nn.Embedding(num_tokens, dim)
def forward(self, x):
token_emb = self.emb(x.long())
return l2norm(token_emb) if self.l2norm_embed else token_emb
def init_(self):
if self.l2norm_embed:
nn.init.normal_(self.emb.weight, std=1e-5)
return
nn.init.kaiming_normal_(self.emb.weight)
# positional embeddings
class AbsolutePositionalEmbedding(Module):
def __init__(self, dim, max_seq_len, l2norm_embed = False):
super().__init__()
self.scale = dim ** -0.5 if not l2norm_embed else 1.
self.max_seq_len = max_seq_len
self.l2norm_embed = l2norm_embed
self.emb = nn.Embedding(max_seq_len, dim)
def forward(self, x, pos = None, seq_start_pos = None):
seq_len, device = x.shape[1], x.device
assert seq_len <= self.max_seq_len, f'you are passing in a sequence length of {seq_len} but your absolute positional embedding has a max sequence length of {self.max_seq_len}'
if not exists(pos):
pos = arange(seq_len, device = device)
if exists(seq_start_pos):
pos = (pos - seq_start_pos[..., None]).clamp(min = 0)
pos_emb = self.emb(pos)
pos_emb = pos_emb * self.scale
return l2norm(pos_emb) if self.l2norm_embed else pos_emb
class ScaledSinusoidalEmbedding(Module):
def __init__(self, dim, theta = 10000):
super().__init__()
assert divisible_by(dim, 2)
self.scale = nn.Parameter(torch.ones(1) * dim ** -0.5)
half_dim = dim // 2
freq_seq = arange(half_dim).float() / half_dim
inv_freq = theta ** -freq_seq
self.register_buffer('inv_freq', inv_freq, persistent = False)
def forward(self, x, pos = None, seq_start_pos = None):
seq_len, device = x.shape[1], x.device
if not exists(pos):
pos = arange(seq_len, device = device)
if exists(seq_start_pos):
pos = pos - seq_start_pos[..., None]
emb = einsum('i, j -> i j', pos, self.inv_freq)
emb = cat((emb.sin(), emb.cos()), dim = -1)
return emb * self.scale
class RelativePositionBias(Module):
def __init__(self, scale, causal = False, num_buckets = 32, max_distance = 128, heads = 8):
super().__init__()
self.scale = scale
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
@property
def device(self):
return next(self.parameters()).device
def forward(self, i, j):
device = self.device
q_pos = arange(j - i, j, dtype = torch.long, device = device)
k_pos = arange(j, dtype = torch.long, device = device)
rel_pos = einx.subtract('j, i -> i j', k_pos, q_pos)
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 bias * self.scale
class CoPE(Module):
"""
Appendix B of https://arxiv.org/abs/2405.18719
"""
def __init__ (
self,
dim,
heads,
max_pos,
soft_onehot = False,
talking_heads = False,
soft_onehot_temp = 5e-2
):
super () . __init__ ()
self.max_pos = max_pos
self.pos_emb = nn.Parameter(torch.zeros(max_pos, dim))
self.talking_heads = nn.Conv2d(heads, heads, 1, bias = False) if talking_heads else None
self.soft_onehot = soft_onehot
self.soft_onehot_temp = soft_onehot_temp
if not soft_onehot:
return
self.register_buffer('positions', arange(max_pos))
def forward(self, query, attn_logits):
if exists(self.talking_heads):
i, j = attn_logits.shape[-2:]
causal_mask = attn_logits.new_ones(i, j).triu_(j - i + 1).bool()
attn_logits = self.talking_heads(attn_logits)
attn_logits = attn_logits.masked_fill(causal_mask, -torch.finfo(attn_logits.dtype).max)
# compute positions
gates = attn_logits.sigmoid()
pos = gates.flip(-1).cumsum(dim = -1).flip(-1)
pos = pos.clamp(max = self.max_pos - 1)
logits_int = einsum('b h n d, p d -> b h n p', query, self.pos_emb)
if self.soft_onehot:
diff_pos = einx.subtract('i, j -> i j', pos, self.positions).abs()
soft_onehot_pos = F.softmax(-diff_pos / self.soft_onehot_temp, dim = -1)
cope_pos_emb = einsum('b h i j p, b h i p -> b h i j', soft_onehot_pos, logits_int)
else:
# interpolate from integer positions
pos_ceil = pos.ceil().long()
pos_floor = pos.floor().long()
logits_ceil = logits_int.gather(-1, pos_ceil)
logits_floor = logits_int.gather(-1, pos_floor)
w = pos - pos_floor
cope_pos_emb = logits_ceil * w + logits_floor * (1 - w)
return cope_pos_emb
class DynamicPositionBias(Module):
def __init__(self, dim, *, heads, depth, log_distance = False, norm = False):
super().__init__()
assert depth >= 1, 'depth for dynamic position bias MLP must be greater or equal to 1'
self.log_distance = log_distance
self.mlp = ModuleList([])
self.mlp.append(Sequential(
nn.Linear(1, dim),
LayerNorm(dim) if norm else None,
nn.SiLU()
))
for _ in range(depth - 1):
self.mlp.append(Sequential(
nn.Linear(dim, dim),
nn.LayerNorm(dim) if norm else None,
nn.SiLU()
))
self.mlp.append(nn.Linear(dim, heads))
@property
def device(self):
return next(self.parameters()).device
def forward(self, i, j):
n, device = j, self.device
# get the (n x n) matrix of distances
seq_arange = arange(j - i, j, device = device)
context_arange = arange(j, device = device)
indices = einx.subtract('i, j -> i j', seq_arange, context_arange)
indices += (j - 1)
# input to continuous positions MLP
pos = arange(-j + 1, j, device = device).float()
pos = rearrange(pos, '... -> ... 1')
if self.log_distance:
pos = torch.sign(pos) * torch.log(pos.abs() + 1) # log of distance is sign(rel_pos) * log(abs(rel_pos) + 1)
for layer in self.mlp:
pos = layer(pos)
# get position biases
bias = pos[indices]
bias = rearrange(bias, 'i j h -> h i j')
return bias
class AlibiPositionalBias(Module):
def __init__(
self,
heads,
total_heads = None,
slopes: list[int] | None = None,
**kwargs
):
super().__init__()
self.heads = heads
self.total_heads = default(total_heads, heads)
slopes = Tensor(default(slopes, self._get_slopes(heads)))
slopes = rearrange(slopes, 'h -> h 1 1')
self.register_buffer('slopes', slopes, persistent = False)
self.register_buffer('bias', None, persistent = False)
@property
def device(self):
return next(self.buffers()).device
@staticmethod
def _get_slopes(heads):
def get_slopes_power_of_2(n):
start = (2**(-2**-(math.log2(n)-3)))
ratio = start
return [start*ratio**i for i in range(n)]
if math.log2(heads).is_integer():
return get_slopes_power_of_2(heads)
closest_power_of_2 = 2 ** math.floor(math.log2(heads))
return get_slopes_power_of_2(closest_power_of_2) + get_slopes_power_of_2(2 * closest_power_of_2)[0::2][:heads-closest_power_of_2]
def forward_custom_pos(
self,
pos_i: Tensor,
pos_j: Tensor | None = None
):
h, device = self.total_heads, self.device
pos_j = default(pos_j, pos_i)
bias = -einx.subtract('... j, ... i -> ... i j', pos_j, pos_i).abs()
if bias.ndim == 3:
bias = rearrange(bias, 'b i j -> b 1 i j')
bias = bias * self.slopes
num_heads_unalibied = h - bias.shape[-3]
bias = pad_at_dim(bias, (0, num_heads_unalibied), dim = -3)
return bias
def forward(self, i, j):
h, device = self.total_heads, self.device
if exists(self.bias) and self.bias.shape[-1] >= j and self.bias.shape[-2] >= i:
return self.bias[..., -i:, -j:]
seq_arange = arange(j - i, j, device = device)
context_arange = arange(j, device = device)
bias = -einx.subtract('j, i -> 1 i j', context_arange, seq_arange).abs()
bias = bias * self.slopes
num_heads_unalibied = h - bias.shape[-3]
bias = pad_at_dim(bias, (0, num_heads_unalibied), dim = -3)
self.register_buffer('bias', bias, persistent = False)
return self.bias
class DataDependentAlibi(Module):
""" https://openreview.net/forum?id=q2Lnyegkr8 """
def __init__(
self,
dim,
heads,
causal = True,
bias_init = 5.,
post_log_scale = 1.,
):
super().__init__()
self.causal = causal
linear = nn.Linear(dim, heads * (1 if causal else 2))
self.to_forget_gates = nn.Sequential(
linear,
Rearrange('b n h -> b h n'),
nn.LogSigmoid()
)
nn.init.constant_(linear.bias, bias_init)
self.post_log_scale = post_log_scale
def forward(self, x):
bidirectional = not self.causal
forget_gates = self.to_forget_gates(x) * self.post_log_scale
forget_gates = forget_gates.cumsum(dim = -1)
if bidirectional:
forget_gates, forget_gates_reversed = forget_gates.chunk(2, dim = 1)
forget_gates = einx.subtract('b h i, b h j -> b h i j', forget_gates, forget_gates)
if bidirectional:
forget_gates_reversed = einx.subtract('b h j, b h i -> b h i j', forget_gates_reversed, forget_gates_reversed)
forget_gates = forget_gates.tril() + forget_gates_reversed.triu()
return forget_gates
class PerRowDataDependentAlibi(Module):
""" same as data dependent alibi from forgetting transformer, but the forgetting gates are also derived by a queries and keys with a small head dimension """
def __init__(
self,
dim,
heads,
causal = True,
dim_head = 8,
post_log_scale = 1.
):
super().__init__()
assert causal, 'bidirectional not supported yet'
self.scale = dim_head ** -0.5
linear = nn.Linear(dim, heads * dim_head * 2, bias = False)
self.to_forget_gates = nn.Sequential(
linear,
Rearrange('b n (qk h d) -> qk b h n d', qk = 2, d = dim_head)
)
self.post_log_scale = post_log_scale
def forward(self, x):
q, k = self.to_forget_gates(x)
forget_gates = einsum('... i d, ... j d -> ... i j', q, k) * self.scale
forget_gates = F.logsigmoid(forget_gates) * self.post_log_scale
# mask out upper triangle + diagonal
n = x.shape[-2]
causal_mask = torch.ones((n, n), dtype = torch.bool, device = x.device).triu()
forget_gates = forget_gates.masked_fill(causal_mask, 0.)
# reverse cumsum
forget_gates = forget_gates.flip(dims = (-1,))
forget_gates = forget_gates.cumsum(dim = -1)
forget_gates = forget_gates.flip(dims = (-1,))
return forget_gates
class RotaryEmbedding(Module):
def __init__(
self,
dim,
use_xpos = False,
scale_base = 512,
interpolation_factor = 1.,
base = 10000,
base_rescale_factor = 1.
):
super().__init__()
# proposed by reddit user bloc97, to rescale rotary embeddings to longer sequence length without fine-tuning
# has some connection to NTK literature
# https://www.reddit.com/r/LocalLLaMA/comments/14lz7j5/ntkaware_scaled_rope_allows_llama_models_to_have/
base *= base_rescale_factor ** (dim / (dim - 2))
inv_freq = 1. / (base ** (arange(0, dim, 2).float() / dim))
self.register_buffer('inv_freq', inv_freq)
assert interpolation_factor >= 1.
self.interpolation_factor = interpolation_factor
if not use_xpos:
self.register_buffer('scale', None)
return
scale = (arange(0, dim, 2) + 0.4 * dim) / (1.4 * dim)
self.scale_base = scale_base
self.register_buffer('scale', scale)
def forward_from_seq_len(self, seq_len):
device = self.inv_freq.device
t = arange(seq_len, device = device)
return self.forward(t)
@autocast('cuda', enabled = False)
def forward(self, t):
max_pos = t.max() + 1
if t.ndim == 1:
t = rearrange(t, 'n -> 1 n')
freqs = torch.einsum('b i , j -> b i j', t.type_as(self.inv_freq), self.inv_freq) / self.interpolation_factor
freqs = stack((freqs, freqs), dim = -1)
freqs = rearrange(freqs, '... d r -> ... (d r)')
if not exists(self.scale):
return freqs, 1.
power = (t - (max_pos // 2)) / self.scale_base
scale = self.scale ** rearrange(power, '... n -> ... n 1')
scale = stack((scale, scale), dim = -1)
scale = rearrange(scale, '... d r -> ... (d r)')
return freqs, scale
def rotate_half(x):
x = rearrange(x, '... (d r) -> ... d r', r = 2)
x1, x2 = x.unbind(dim = -1)
x = stack((-x2, x1), dim = -1)
return rearrange(x, '... d r -> ... (d r)')
@autocast('cuda', enabled = False)
def apply_rotary_pos_emb(t, freqs, scale = 1):
rot_dim, seq_len, orig_dtype = freqs.shape[-1], t.shape[-2], t.dtype
freqs = freqs[:, -seq_len:, :]
scale = scale[:, -seq_len:, :] if isinstance(scale, torch.Tensor) else scale
if t.ndim == 4 and freqs.ndim == 3:
freqs = rearrange(freqs, 'b n d -> b 1 n d')
# partial rotary embeddings, Wang et al. GPT-J
t, t_unrotated = t[..., :rot_dim], t[..., rot_dim:]
t = (t * freqs.cos() * scale) + (rotate_half(t) * freqs.sin() * scale)
out = cat((t, t_unrotated), dim = -1)
return out.type(orig_dtype)
# norms
class Scale(Module):
def __init__(self, value, fn):
super().__init__()
self.value = value
self.fn = fn
def forward(self, x, **kwargs):
out = self.fn(x, **kwargs)
scale_fn = lambda t: t * self.value
if not isinstance(out, tuple):
return scale_fn(out)
return (scale_fn(out[0]), *out[1:])
class LayerNorm(Module):
def __init__(
self,
dim,
unit_offset = False
):
"""
bias-less layernorm has been shown to be more stable. most newer models have moved towards rmsnorm, also bias-less
"""
super().__init__()
self.unit_offset = unit_offset
self.ln = nn.LayerNorm(dim, elementwise_affine = False)
self.gamma = nn.Parameter(torch.ones(dim))
nn.init.constant_(self.gamma, 1. - float(unit_offset))
def forward(self, x):
normed = self.ln(x)
gamma = self.gamma + float(self.unit_offset)
return normed * gamma
class AdaptiveLayerNorm(Module):
def __init__(
self,
dim,
dim_condition = None
):
super().__init__()
dim_condition = default(dim_condition, dim)
self.ln = nn.LayerNorm(dim, elementwise_affine = False)
self.to_gamma = LinearNoBias(dim_condition, dim)
nn.init.zeros_(self.to_gamma.weight)
def forward(self, x, *, condition):
if condition.ndim == 2:
condition = rearrange(condition, 'b d -> b 1 d')
normed = self.ln(x)
gamma = self.to_gamma(condition)
return normed * (gamma + 1.)
class ScaleNorm(Module):
def __init__(
self,
dim,
unit_offset = False
):
super().__init__()
self.unit_offset = unit_offset
self.scale = dim ** 0.5
self.g = nn.Parameter(torch.zeros(1))
nn.init.constant_(self.g, 1. - float(unit_offset))
def forward(self, x):
gamma = self.g + float(self.unit_offset)
return F.normalize(x, dim = -1) * self.scale * gamma
class RMSNorm(Module):
def __init__(
self,
dim,
unit_offset = False
):
super().__init__()
self.unit_offset = unit_offset
self.scale = dim ** 0.5
self.g = nn.Parameter(torch.zeros(dim))
nn.init.constant_(self.g, 1. - float(unit_offset))
def forward(self, x):
gamma = self.g + float(self.unit_offset)
return F.normalize(x, dim = -1) * self.scale * gamma
class AdaptiveRMSNorm(Module):
def __init__(
self,
dim,
dim_condition = None
):
super().__init__()
self.scale = dim ** 0.5
dim_condition = default(dim_condition, dim)
self.to_gamma = LinearNoBias(dim_condition, dim)
nn.init.zeros_(self.to_gamma.weight)
def forward(self, x, *, condition):
if condition.ndim == 2:
condition = rearrange(condition, 'b d -> b 1 d')
normed = F.normalize(x, dim = -1)
gamma = self.to_gamma(condition)
return normed * self.scale * (gamma + 1.)
class SimpleRMSNorm(Module):
def __init__(
self,
dim,
**kwargs
):
super().__init__()
self.scale = dim ** 0.5
def forward(self, x):
return F.normalize(x, dim = -1) * self.scale
class MultiheadRMSNorm(Module):
def __init__(self, dim, heads):
super().__init__()
self.rmsnorm = SimpleRMSNorm(dim)
self.gamma = nn.Parameter(torch.zeros(heads, 1, dim))
def forward(self, x):
return self.rmsnorm(x) * (self.gamma + 1.)
class DynamicTanh(Module):
""" https://arxiv.org/abs/2503.10622 """
def __init__(
self,
dim,
init_alpha = 1.,
gamma = 1.,
beta = 0.,
unit_offset = False
):
super().__init__()
self.pre_tanh_scale = nn.Parameter(tensor(init_alpha))
self.gamma = nn.Parameter(torch.ones(dim))
self.beta = nn.Parameter(torch.zeros(dim))
self.pre_tanh_scale_offset = init_alpha if unit_offset else 0.
self.gamma_offset = float(unit_offset)
nn.init.constant_(self.pre_tanh_scale, 0 if unit_offset else init_alpha)
nn.init.constant_(self.gamma, 1. - float(unit_offset))
def forward(self, x):
pre_tanh_scale = self.pre_tanh_scale + self.pre_tanh_scale_offset
gamma = self.gamma + self.gamma_offset
return (x * pre_tanh_scale).tanh() * gamma + self.beta
# residual and residual gates
class Residual(Module):
def __init__(self, dim, scale_residual = False, scale_residual_constant = 1., **kwargs):
super().__init__()
self.residual_scale = nn.Parameter(torch.ones(dim)) if scale_residual else None
self.scale_residual_constant = scale_residual_constant
def prepare(self, residual):
return residual, residual, dict()
def forward(self, x, residual, **kwargs):
if exists(self.residual_scale):
residual = residual * self.residual_scale
if self.scale_residual_constant != 1:
residual = residual * self.scale_residual_constant
return x + residual
class GRUGating(Module):
def __init__(self, dim, scale_residual = False, **kwargs):
super().__init__()
self.gru = nn.GRUCell(dim, dim)
self.residual_scale = nn.Parameter(torch.ones(dim)) if scale_residual else None
def prepare(self, residual):
return residual, residual, dict()
def forward(self, x, residual, **kwargs):
if exists(self.residual_scale):
residual = residual * self.residual_scale
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)
# hyper connections
class HyperConnection(Module):
def __init__(
self,
dim,
*,
layer_index,
num_residual_streams,
num_input_views = 1,
tanh = True,
**kwargs
):
"""
https://arxiv.org/abs/2409.19606
Appendix J - Algorithm 2, Dynamic only
"""
super().__init__()
self.act = nn.Tanh() if tanh else nn.Identity()
self.norm = nn.LayerNorm(dim, bias = False)
self.num_residual_streams = num_residual_streams
self.layer_index = layer_index
self.static_beta = nn.Parameter(torch.ones(num_residual_streams))
init_alpha0 = torch.zeros((num_residual_streams, num_input_views))
init_alpha0[layer_index % num_residual_streams, :] = 1.
self.static_alpha = nn.Parameter(cat([init_alpha0, torch.eye(num_residual_streams)], dim = 1))
self.dynamic_alpha_fn = nn.Parameter(torch.zeros(dim, num_residual_streams + num_input_views))
self.dynamic_alpha_scale = nn.Parameter(torch.ones(()) * 1e-2)
self.num_input_views = num_input_views
self.dynamic_beta_fn = nn.Parameter(torch.zeros(dim))
self.dynamic_beta_scale = nn.Parameter(torch.ones(()) * 1e-2)
def prepare(self, residuals):
residuals = rearrange(residuals, '(b s) n d -> b n s d', s = self.num_residual_streams)
normed = self.norm(residuals)
wc_weight = self.act(normed @ self.dynamic_alpha_fn)
dynamic_alpha = wc_weight * self.dynamic_alpha_scale
alpha = dynamic_alpha + self.static_alpha
dc_weight = self.act(normed @ self.dynamic_beta_fn)
dynamic_beta = dc_weight * self.dynamic_beta_scale
beta = dynamic_beta + self.static_beta
# width connection
mix_h = einsum('... s t, ... s d -> ... t d', alpha, residuals)
views = self.num_input_views
if views == 1:
branch_input, residuals = mix_h[..., 0, :], mix_h[..., 1:, :]
else:
branch_input, residuals = mix_h[..., :views, :], mix_h[..., views:, :]
branch_input = rearrange(branch_input, '... v d -> v ... d')
return branch_input, residuals, dict(beta = beta)
def forward(self, x, residuals, *, beta):
residuals = einsum('b n d, b n s -> b n s d', x, beta) + residuals
return rearrange(residuals, 'b n s d -> (b s) n d')
# LIMe - layer integrated memory (dynamic version)
class DynamicLIMe(Module):
def __init__(
self,
dim,
num_layers,
num_views = 1,
norm = True,
use_softmax = True
):
super().__init__()
self.num_layers = num_layers
self.multiple_views = num_views > 1
self.to_weights = Sequential(
RMSNorm(dim) if norm else None,
nn.Linear(dim, num_views * num_layers),
Rearrange('... (views layers) -> views ... layers', views = num_views),
nn.Softmax(dim = -1) if use_softmax else nn.ReLU()
)
def forward(
self,
x,
hiddens
):
if not is_tensor(hiddens):
hiddens = stack(hiddens)
assert hiddens.shape[0] == self.num_layers, f'expected hiddens to have {self.num_layers} layers but received {tuple(hiddens.shape)} instead (first dimension must be layers)'
weights = self.to_weights(x)
out = einsum('l b n d, v b n l -> v b n d', hiddens, weights)
if self.multiple_views:
return out
return rearrange(out, '1 ... -> ...')
# token shifting
def shift(t, amount, mask = None):
if amount == 0:
return t
amount = min(amount, t.shape[1])
if exists(mask):
t = t.masked_fill(~mask[..., None], 0.)
return pad_at_dim(t, (amount, -amount), dim = - 2, value = 0.)
class ShiftTokens(Module):
def __init__(self, shifts, fn):
super().__init__()
self.fn = fn
self.shifts = tuple(shifts)
def forward(self, x, **kwargs):
mask = kwargs.get('mask', None)
shifts = self.shifts
segments = len(shifts)
feats_per_shift = x.shape[-1] // segments
splitted = x.split(feats_per_shift, dim = -1)
segments_to_shift, rest = splitted[:segments], splitted[segments:]
segments_to_shift = [shift(*args, mask = mask) for args in zip(segments_to_shift, shifts)]
x = cat((*segments_to_shift, *rest), dim = -1)
return self.fn(x, **kwargs)
class FoldAxially(Module):
def __init__(
self,
axial_dim,
fn: Module
):
super().__init__()
self.fn = fn
self.axial_dim = axial_dim # will fold the sequence as rearrange("b (n axial_dim) ... -> (b axial_dim) n ...")
def forward(
self,
x,
**kwargs
):
if self.axial_dim == 1:
return self.fn(x, **kwargs)
seq_len, axial_dim = x.shape[1], self.axial_dim
next_multiple = math.ceil(seq_len / axial_dim) * axial_dim
x = pad_at_dim(x, (0, next_multiple - seq_len), dim = 1)
x = rearrange(x, 'b (n axial_dim) ... -> (b axial_dim) n ...', axial_dim = axial_dim)
out = self.fn(x, **kwargs)
(out, *rest_out), tree_spec = tree_flatten(out)
out = rearrange(out, '(b axial_dim) n ... -> b (n axial_dim) ...', axial_dim = axial_dim)
out = out[:, :seq_len]
out = tree_unflatten((out, *rest_out), tree_spec)
return out
# post branch operator
class LayerScale(Module):
def __init__(
self,
fn: Module,
dim,
init_value = 0.,
unit_offset = False
):
super().__init__()
self.unit_offset = unit_offset
self.fn = fn
self.gamma = nn.Parameter(torch.zeros(dim))
nn.init.constant_(self.gamma, init_value - float(unit_offset))
def forward(self, x, **kwargs):
out = self.fn(x, **kwargs)
gamma = self.gamma + float(self.unit_offset)
if isinstance(out, Tensor):
return out * gamma
out, *rest = out
return out * gamma, *rest
class AdaptiveLayerScale(Module):
def __init__(
self,
fn: Module,
dim,
dim_condition = None,
init_bias_value = -2.
):
super().__init__()
self.fn = fn
dim_condition = default(dim_condition, dim)
self.to_gamma = nn.Linear(dim_condition, dim)
nn.init.zeros_(self.to_gamma.weight)
nn.init.constant_(self.to_gamma.bias, init_bias_value)
def forward(self, x, *, condition, **kwargs):
if condition.ndim == 2:
condition = rearrange(condition, 'b d -> b 1 d')
out = self.fn(x, **kwargs)
gamma = self.to_gamma(condition).sigmoid()
if isinstance(out, Tensor):
return out * gamma
out, *rest = out
return out * gamma, *rest
# skip connection combining
class ConcatCombine(Module):
def __init__(self, dim, prev_layer_ind):
super().__init__()
self.prev_layer_ind = prev_layer_ind
self.combine = LinearNoBias(dim * 2, dim)
def forward(self, x, prev_layers: list[Tensor]):
skip = prev_layers[self.prev_layer_ind]
concatted_skip = cat((skip, x), dim = -1)
return self.combine(concatted_skip)
# feedforward
class GLU(Module):
def __init__(
self,
dim_in,
dim_out,
activation: Callable,
mult_bias = False
):
super().__init__()
self.act = activation
self.proj = nn.Linear(dim_in, dim_out * 2)
self.mult_bias = nn.Parameter(torch.ones(dim_out)) if mult_bias else 1.
def forward(self, x):
x, gate = self.proj(x).chunk(2, dim = -1)
return x * self.act(gate) * self.mult_bias
class FeedForward(Module):
def __init__(
self,
dim,
dim_out = None,
mult = 4,
glu = False,
glu_mult_bias = False,
swish = False,
relu_squared = False,
custom_activation = None,
post_act_ln = False,
dropout = 0.,
sublayer_dropout = 0.,
no_bias = False,
zero_init_output = False
):
super().__init__()
inner_dim = int(dim * mult)
dim_out = default(dim_out, dim)
if exists(custom_activation):
activation = deepcopy(custom_activation)
elif relu_squared:
activation = ReluSquared()
elif swish:
activation = nn.SiLU()
else:
activation = nn.GELU()
if glu:
project_in = GLU(dim, inner_dim, activation, mult_bias = glu_mult_bias)
else:
project_in = nn.Sequential(
nn.Linear(dim, inner_dim, bias = not no_bias),
activation
)
self.ff = Sequential(
project_in,
LayerNorm(inner_dim) if post_act_ln else None,
nn.Dropout(dropout),
nn.Linear(inner_dim, dim_out, bias = not no_bias),
nn.Dropout(sublayer_dropout) if sublayer_dropout > 0. else None
)
# init last linear layer to 0
if zero_init_output:
init_zero_(self.ff[-1])
def forward(self, x):
return self.ff(x)
# attention. it is all we need
class Attention(Module):
def __init__(
self,
dim,
dim_head = DEFAULT_DIM_HEAD,
dim_context = None,
heads = 8,
causal = False,
flash = False,
pre_talking_heads = False,
post_talking_heads = False,
pre_scale_post_talking_heads = False,
head_scale = False,
sparse_topk = None,
sparse_topk_straight_through = False,
num_mem_kv = 0,
dropout = 0.,
sublayer_dropout = 0.,
on_attn = False,
gate_value_heads = False,
swiglu_values = False,
gate_values = False,
zero_init_output = False,
hard = False,
max_attend_past = None,
qk_norm = False,
qk_norm_groups = 1,
qk_norm_scale = 10,
qk_norm_dim_scale = False,
l2_distance = False,
sigmoid = False,
selective = False,
custom_attn_fn: Callable | None = None,
hybrid_module: Module | None = None,
hybrid_mask_kwarg: str | None = None,
hybrid_fold_axial_dim: int | None = None,
hybrid_learned_mix = False,
one_kv_head = False,
kv_heads = None,
value_dim_head = None,
dim_out = None,
add_zero_kv = False, # same as add_zero_attn in pytorch
rotate_num_heads = None,
data_dependent_alibi = False,
data_dependent_alibi_per_row = False,
data_dependent_alibi_per_row_dim_head = 8,
data_dependent_alibi_kwargs: dict = dict(),
use_cope = False,
cope_max_pos = 16,
cope_soft_onehot_pos = False,
cope_talking_heads = False,
softclamp_logits = False,
logit_softclamp_value = 50.,
learned_value_residual_mix = False,
laser = False, # https://arxiv.org/abs/2411.03493v1
laser_softclamp_value = 15.,
qkv_receive_diff_residuals = False,
use_latent_q = False,
dim_latent_q = None,
use_latent_kv = False,
dim_latent_kv = None,
latent_rope_subheads = None,
onnxable = False,
attend_sdp_kwargs: dict = dict(
enable_flash = True,
enable_math = True,
enable_mem_efficient = True
)
):
super().__init__()
dim_kv = default(dim_context, dim)
self.scale = dim_head ** -0.5
self.heads = heads
self.causal = causal
self.max_attend_past = max_attend_past
assert not (exists(kv_heads) and one_kv_head), 'either attn_one_kv_head is set to True (in which case kv_heads is set to 1), or attn_kv_heads is set, but not both'
value_dim_head = default(value_dim_head, dim_head)
kv_heads = default(kv_heads, heads)
kv_heads = 1 if one_kv_head else kv_heads
assert divisible_by(heads, kv_heads)
self.kv_heads = kv_heads
q_dim = dim_head * heads
k_dim = dim_head * kv_heads
v_dim = value_dim_head * kv_heads
out_dim = value_dim_head * heads
# determine input dimensions to qkv based on whether intermediate latent q and kv are being used
# for eventually supporting multi-latent attention (MLA)
self.to_latent_q = None
self.to_latent_kv = None
self.to_rotateable_k = None # for their "decoupled rope", subheads of keys that comes directly from base sequence (does not go through latents)
dim_q_input = dim
dim_kv_input = dim_kv
if use_latent_q:
assert exists(dim_latent_q)
self.to_latent_q = LinearNoBias(dim, dim_latent_q)
dim_q_input = dim_latent_q
if use_latent_kv:
assert exists(dim_latent_kv)
self.to_latent_kv = LinearNoBias(dim, dim_latent_kv)
dim_kv_input = dim_latent_kv
if exists(latent_rope_subheads):
assert not exists(rotate_num_heads), '`rotate_num_heads` cannot be set when multi-latent attention is being used'
rotate_num_heads = latent_rope_subheads
k_dim = dim_head * (kv_heads - latent_rope_subheads)
self.to_rotateable_k = LinearNoBias(dim, dim_head * latent_rope_subheads)
self.split_rotateable_k_heads = Rearrange('b n (h d) -> b h n d', h = latent_rope_subheads)
self.use_latent_q = use_latent_q
self.use_latent_kv = use_latent_kv
# query key projection
self.to_q = LinearNoBias(dim_q_input, q_dim)
self.to_k = LinearNoBias(dim_kv_input, k_dim)
self.to_v = LinearNoBias(dim_kv_input, v_dim)
# split and merge of attention heads
self.split_q_heads = Rearrange('b n (h d) -> b h n d', h = heads)
self.split_k_heads = Rearrange('b n (h d) -> b h n d', d = dim_head)
self.split_v_heads = Rearrange('b n (h d) -> b h n d', d = value_dim_head)
self.merge_heads = Rearrange('b h n d -> b n (h d)')
# whether qkv receives different residual stream combinations from hyper connections or lime
self.qkv_receive_diff_residuals = qkv_receive_diff_residuals
# enhancing gradients to attention through exponentiated values
self.laser = laser
self.laser_softclamp_value = laser_softclamp_value
# add GLU gating for aggregated values, from alphafold2
self.to_v_gate = None
if gate_values:
self.to_v_gate = nn.Linear(dim, out_dim)
self.to_v_gate_activation = F.silu if swiglu_values else F.sigmoid
nn.init.constant_(self.to_v_gate.weight, 0)
nn.init.constant_(self.to_v_gate.bias, 10)
# add per head gating of the output values, from 'Attend to nothing' paper
self.to_v_head_gate = None
if gate_value_heads:
self.to_v_head_gate = nn.Linear(dim, heads)
nn.init.constant_(self.to_v_head_gate.weight, 0)
nn.init.constant_(self.to_v_head_gate.bias, 10)
# cosine sim attention
self.qk_norm = qk_norm
self.qk_norm_groups = qk_norm_groups
self.qk_norm_scale = qk_norm_scale
# whether to use the rmsnorm (equivalent to cosine sim attention when scale is equal to 1) - https://arxiv.org/abs/2302.05442
self.qk_norm_dim_scale = qk_norm_dim_scale
self.qk_norm_q_scale = self.qk_norm_k_scale = 1
if qk_norm and qk_norm_dim_scale:
self.qk_norm_q_scale = nn.Parameter(torch.ones(heads, 1, dim_head))
self.qk_norm_k_scale = nn.Parameter(torch.ones(kv_heads, 1, dim_head))
assert (not qk_norm) or divisible_by(dim_head, qk_norm_groups), 'dimension per attention head must be divisible by the qk norm groups'
assert not (qk_norm and (dim_head // qk_norm_groups) <= 2), 'the group dimension may be too small (2 was too small in my tests, but 4 still works, surprisingly)'
# contextual positional encoding
# https://arxiv.org/html/2405.18719v2
cope = None
if use_cope:
assert causal, 'CoPE was designed for causal attention'
assert not flash, 'CoPE is not flash attention compatible'
cope = CoPE(
dim = dim_head,
heads = heads,
max_pos = cope_max_pos,
talking_heads = cope_talking_heads,
soft_onehot = cope_soft_onehot_pos
)
# data dependent alibi
# https://openreview.net/forum?id=q2Lnyegkr8
self.data_dependent_alibi = None
if data_dependent_alibi:
dda_klass = DataDependentAlibi if not data_dependent_alibi_per_row else PerRowDataDependentAlibi
dda_kwargs = dict(dim = dim, heads = heads, causal = causal)
if data_dependent_alibi_per_row:
dda_kwargs.update(dim_head = data_dependent_alibi_per_row_dim_head)
self.data_dependent_alibi = dda_klass(**dda_kwargs, **data_dependent_alibi_kwargs)
# attend class - includes core attention algorithm + talking heads
self.attend = Attend(
heads = heads,
causal = causal,
pre_talking_heads = pre_talking_heads,
post_talking_heads = post_talking_heads,
pre_scale_post_talking_heads = pre_scale_post_talking_heads,
dropout = dropout,
sparse_topk = sparse_topk,
sparse_topk_straight_through = sparse_topk_straight_through,
hard = hard,
qk_norm = qk_norm,
scale = qk_norm_scale if qk_norm else self.scale,
l2_distance = l2_distance,
sigmoid = sigmoid,
selective = selective,
custom_attn_fn = custom_attn_fn,
add_zero_kv = add_zero_kv,
flash = flash,
softclamp_logits = softclamp_logits,
logit_softclamp_value = logit_softclamp_value,
cope = cope,
onnxable = onnxable,
sdp_kwargs = attend_sdp_kwargs
)
# head scaling
self.head_scale = head_scale
if head_scale:
self.head_scale_params = nn.Parameter(torch.ones(1, heads, 1, 1))
# explicit topk sparse attention
self.sparse_topk = sparse_topk
# add memory key / values
self.num_mem_kv = num_mem_kv
if num_mem_kv > 0:
self.mem_k = nn.Parameter(torch.randn(kv_heads, num_mem_kv, dim_head))
self.mem_v = nn.Parameter(torch.randn(kv_heads, num_mem_kv, dim_head))
# maybe learned value residual mixer per token
self.to_value_residual_mix = nn.Sequential(
nn.Linear(dim, heads),
nn.Sigmoid(),
Rearrange('b n h -> b h n 1')
) if learned_value_residual_mix else always(0.5)
# attention on attention
self.attn_on_attn = on_attn
# hybrid module, in same vein as hymba https://www.arxiv.org/abs/2411.13676
hybrid_mix = None
hybrid_norms = None
hybrid_module = maybe(deepcopy)(hybrid_module)
if exists(hybrid_module) and exists(hybrid_fold_axial_dim):
hybrid_module = FoldAxially(axial_dim = hybrid_fold_axial_dim, fn = hybrid_module)
hybrid_mix = LinearNoBias(dim, heads) if hybrid_learned_mix else None
hybrid_norms = ModuleList([
MultiheadRMSNorm(dim_head, heads = heads),
MultiheadRMSNorm(dim_head, heads = heads)
])
self.hybrid_module = hybrid_module
self.hybrid_norms = hybrid_norms
self.hybrid_mix = hybrid_mix
self.hybrid_mask_kwarg = hybrid_mask_kwarg # for bidirectional, can forward `mask` into the hybrid module and let it handle variable lengths
# output dimension by default same as input, but can be overridden
dim_out = default(dim_out, dim)
self.to_out = nn.Sequential(LinearNoBias(out_dim, dim_out * 2), nn.GLU()) if on_attn else LinearNoBias(out_dim, dim_out)
# sublayer dropout
self.sublayer_dropout = nn.Dropout(sublayer_dropout) if sublayer_dropout > 0. else None
# the number of attention heads to rotate, for decoupled rope in multi-latent attention
rotate_num_heads = default(rotate_num_heads, heads)
assert 0 < rotate_num_heads <= heads
is_partial_rotate_heads = rotate_num_heads < heads
assert not (is_partial_rotate_heads and kv_heads < heads), 'grouped query attention not compatible with partial rotate heads (decoupled rope for multi-latent attention), yet'
self.rotate_num_heads = rotate_num_heads
# whether parent can kv cache
self.can_cache_kv = not selective
# init output projection 0
if zero_init_output:
init_zero_(self.to_out)
def forward(
self,
x,
context = None,
mask = None,
context_mask = None,
attn_mask = None,
rel_pos = None,
attn_bias = None,
rotary_pos_emb = None,
context_rotary_pos_emb = None,
pos = None, # for custom alibi positions
prev_attn = None,
mem = None,
mem_mask = None,
return_intermediates = False,
cache: Intermediates | None = None,
value_residual = None
):
b, n, h, kv_h, head_scale, num_mem_kv, device, has_context, qkv_receive_diff_residuals, is_multi_latent_attn = x.shape[0], x.shape[1], self.heads, self.kv_heads, self.head_scale, self.num_mem_kv, x.device, exists(context), self.qkv_receive_diff_residuals, self.use_latent_kv
# an interesting possibility with hyper connections
# having queries, keys, values be routed from different layers
assert not (qkv_receive_diff_residuals and has_context), 'qkv receiving different sequences can only be used for self attention'
if qkv_receive_diff_residuals:
assert x.ndim == 4 and x.shape[0] == 3
q_input, k_input, v_input = x
else:
kv_input = default(context, x)
q_input, k_input, v_input = x, kv_input, kv_input
if exists(mem):
k_input, mem_packed_shape = pack([mem, k_input], 'b * d')
v_input, _ = pack([mem, v_input], 'b * d')
# multi-latent attention logic
# https://arxiv.org/abs/2405.04434 - Deepseek-AI team
k_sub_heads = None # the rotateable subheads of keys derived from base sequence
if self.use_latent_q:
q_input = self.to_latent_q(q_input)
if is_multi_latent_attn:
assert not qkv_receive_diff_residuals
needs_k_sub_heads = exists(self.to_rotateable_k)
latent_kv_input = self.to_latent_kv(k_input)
if needs_k_sub_heads:
rotateable_k = self.to_rotateable_k(k_input)
k_sub_heads = self.split_rotateable_k_heads(rotateable_k)
if exists(cache):
cached_latent_kv, maybe_cached_k_sub_heads = cache.cached_kv
latent_kv_input = cat((cached_latent_kv, latent_kv_input), dim = -2)
if exists(maybe_cached_k_sub_heads):
k_sub_heads = cat((maybe_cached_k_sub_heads, k_sub_heads), dim = -2)
if return_intermediates:
cached_kv = (latent_kv_input, k_sub_heads)
k_input = v_input = latent_kv_input
# query, key, value projection
q = self.to_q(q_input)
k = self.to_k(k_input)
v = self.to_v(v_input)
q = self.split_q_heads(q)
k = self.split_k_heads(k)
v = self.split_v_heads(v)
# take care of decoupled rope from multi-latent attention
if exists(k_sub_heads):
k = cat((k, k_sub_heads), dim = 1)
# if previous values passed in for residual, either invoke resformer
orig_values = v
# https://arxiv.org/abs/2410.17897v1
if exists(value_residual):
value_residual_mix = self.to_value_residual_mix(q_input)
v = value_residual.lerp(v, value_residual_mix)
# qk normalization
if self.qk_norm:
qk_l2norm = partial(l2norm, groups = self.qk_norm_groups)
q, k = map(qk_l2norm, (q, k))
scale = self.qk_norm_scale
q = q * self.qk_norm_q_scale
k = k * self.qk_norm_k_scale
# take care of caching
if not is_multi_latent_attn:
if exists(cache):
ck, cv = cache.cached_kv
if exists(mem):
mk, k = unpack(k, mem_packed_shape, 'b h * d')
mv, v = unpack(v, mem_packed_shape, 'b h * d')
k = cat((ck, k), dim = -2)
v = cat((cv, v), dim = -2)
if exists(mem):
k = cat((mk, k), dim = -2)
v = cat((mv, v), dim = -2)
if return_intermediates:
mem_len = mem.shape[-2] if exists(mem) else 0
cached_kv = (k[..., mem_len:, :], v[..., mem_len:, :])
if exists(rotary_pos_emb):
rotate_num_heads = self.rotate_num_heads
partial_rotate_heads = rotate_num_heads < h
freqs, xpos_scale = rotary_pos_emb
q_xpos_scale, k_xpos_scale = (xpos_scale, xpos_scale ** -1.) if exists(xpos_scale) else (1., 1.)
if partial_rotate_heads:
q_rest, q = q[:, :-rotate_num_heads], q[:, -rotate_num_heads:]
k_rest, k = k[:, :-rotate_num_heads], k[:, -rotate_num_heads:]
q = apply_rotary_pos_emb(q, freqs, q_xpos_scale)
if has_context:
# override with `context_rotary_pos_emb` if provided
freqs, xpos_scale = context_rotary_pos_emb
_, k_xpos_scale = (xpos_scale, xpos_scale ** -1.) if exists(xpos_scale) else (1., 1.)
k = apply_rotary_pos_emb(k, freqs, k_xpos_scale)
if partial_rotate_heads:
q = cat((q_rest, q), dim = 1)
k = cat((k_rest, k), dim = 1)
input_mask = context_mask
if not exists(input_mask) and not has_context:
input_mask = mask
if (exists(input_mask) or exists(mem_mask)) and exists(mem):
seq_len, mem_len = n, mem.shape[-2]
if not exists(mem_mask):
input_mask = pad_at_dim(input_mask, (mem_len, 0), dim = -1, value = True)
elif not exists(input_mask):
input_mask = pad_at_dim(mem_mask, (0, seq_len), dim = -1, value = True)
else:
input_mask = cat((mem_mask, input_mask), dim = -1)
# i, j determined for relative positional bias, excluding memory key / values
i, j = tuple(t.shape[-2] for t in (q, k))
# maybe append memory key / values
if num_mem_kv > 0:
mem_k, mem_v = tuple(repeat(t, 'h n d -> b h n d', b = b) for t in (self.mem_k, self.mem_v))
if self.qk_norm:
mem_k = l2norm(mem_k)
mem_k = mem_k * self.qk_norm_k_scale
k = cat((mem_k, k), dim = -2)
v = cat((mem_v, v), dim = -2)
if exists(input_mask):
input_mask = pad_at_dim(input_mask, (self.num_mem_kv, 0), dim = -1, value = True)
# determine masking
mask_value = max_neg_value(q)
masks = []
final_attn_mask = None
if exists(input_mask):
input_mask = rearrange(input_mask, 'b j -> b 1 1 j')
masks.append(~input_mask)
if exists(attn_mask):
assert 2 <= attn_mask.ndim <= 4, 'attention mask must have greater than 2 dimensions but less than or equal to 4'
if attn_mask.ndim == 2:
attn_mask = rearrange(attn_mask, 'i j -> 1 1 i j')
elif attn_mask.ndim == 3:
attn_mask = rearrange(attn_mask, 'h i j -> 1 h i j')
masks.append(~attn_mask)
if exists(self.max_attend_past):
range_q = arange(j - i, j, device = device)
range_k = arange(j, device = device)
dist = einx.subtract('i, j -> 1 1 i j', range_q, range_k)
max_attend_past_mask = dist > self.max_attend_past
max_attend_past_mask = pad_at_dim(max_attend_past_mask, (num_mem_kv, 0), value = False, dim = -1) # handle memory key / values
masks.append(max_attend_past_mask)
if len(masks) > 0:
final_attn_mask = ~or_reduce(masks)
# prepare relative positional bias, if needed
if exists(rel_pos):
assert not exists(attn_bias)
if exists(pos):
assert isinstance(rel_pos, AlibiPositionalBias), 'only alibi allowed for custom positions at the moment'
# allow for custom positions to be passed in
attn_bias = rel_pos.forward_custom_pos(pos)
else:
attn_bias = rel_pos(i, j)
attn_bias = pad_at_dim(attn_bias, (num_mem_kv, 0)) # handle memory key / values
# prepare data dependent alibi from forgetting transformers paper, if needed
if exists(self.data_dependent_alibi):
attn_bias = self.data_dependent_alibi(x)
attn_bias = pad_at_dim(attn_bias, (num_mem_kv, 0))
if self.laser:
v = softclamp(v, self.laser_softclamp_value)
v = v.exp()
# attention is all we need
out, intermediates = self.attend(
q, k, v,
mask = final_attn_mask,
attn_bias = attn_bias,
prev_attn = prev_attn
)
# laser
if self.laser:
out = log(out)
# store the values for resformer
intermediates.values = orig_values
# normformer scaling of heads
if head_scale:
out = out * self.head_scale_params
# per head gating, from https://arxiv.org/abs/2306.12929
if exists(self.to_v_head_gate):
head_gate = self.to_v_head_gate(x)
out = einx.multiply('b n h, b h n d ->b h n d', head_gate.sigmoid(), out)
# if exists hybrid module, must do a normalization
# hybrid module
if exists(self.hybrid_module):
# hybrid input
hybrid_forward_kwargs = dict()
if not self.causal and exists(self.hybrid_mask_kwarg):
hybrid_forward_kwargs = {self.hybrid_mask_kwarg: mask}
# hybrid forward
hybrid_outputs = self.hybrid_module(x, **hybrid_forward_kwargs)
# handle hybrid out
(hybrid_out, *rest_hybrid_outs), _ = tree_flatten(hybrid_outputs)
# handle variable hybrid output and multi rmsnorm before summing to main attention output (also normed)
if hybrid_out.ndim == 3:
hybrid_out = rearrange(hybrid_out, 'b n (h d) -> b h n d', h = h)
out_norm, hybrid_out_norm = self.hybrid_norms
out = out_norm(out)
hybrid_out = hybrid_out_norm(hybrid_out)
if exists(self.hybrid_mix):
mix = self.hybrid_mix(x)
mix = rearrange(mix, 'b n h -> b h n 1')
out = out.lerp(hybrid_out, mix.sigmoid())
else:
out = 0.5 * (out + hybrid_out)
# merge heads
out = self.merge_heads(out)
# alphafold2 styled gating of the values
if exists(self.to_v_gate):
gates = self.to_v_gate(x)
out = out * self.to_v_gate_activation(gates)
# combine the heads
out = self.to_out(out)
# maybe sublayer dropout
out = maybe(self.sublayer_dropout)(out)
if exists(mask):
out = einx.where('b n, b n d, -> b n d', mask, out, 0.)
if not return_intermediates:
return out
intermediates.cached_kv = cached_kv
return out, intermediates
class AttentionLayers(Module):
def __init__(
self,
dim,
depth = None,
heads = 8,
causal = False,
cross_attend = False,
only_cross = False,
use_scalenorm = False,
use_rmsnorm = False,
use_dynamic_tanh = False,
dynamic_tanh_init_alpha = 1.,
use_simple_rmsnorm = False,
use_adaptive_layernorm = False,
use_adaptive_rmsnorm = False,
use_adaptive_layerscale = False, # paired with use_adaptive_layernorm for ada-ln-zero from DiT paper
norm_add_unit_offset = True,
dim_condition = None,
adaptive_condition_mlp = False,
adaptive_condition_mlp_expansion = 4,
alibi_pos_bias = False,
alibi_num_heads = None,
rel_pos_bias = False,
rel_pos_num_buckets = 32,
rel_pos_max_distance = 128,
dynamic_pos_bias = False,
dynamic_pos_bias_log_distance = False,
dynamic_pos_bias_mlp_depth = 2,
dynamic_pos_bias_norm = False,
rotary_pos_emb = False,
rotary_emb_dim = None,
rotary_xpos = False,
rotary_interpolation_factor = 1.,
rotary_xpos_scale_base = 512,
rotary_base_rescale_factor = 1.,
rotate_num_heads = None,
weight_tie_layers = False,
custom_layers: tuple[str, ...] | None = None,
layers_execute_order: tuple[int, ...] | None = None,
sandwich_coef = None,
par_ratio = None,
residual_attn = False,
cross_residual_attn = False,
macaron = False,
pre_norm = True,
pre_norm_has_final_norm = True,
gate_residual = False,
scale_residual = False,
scale_residual_constant = 1.,
shift_tokens = 0,
sandwich_norm = False,
softclamp_output = False,
softclamp_output_value = 30.,
zero_init_branch_output = False,
layer_dropout = 0.,
cross_attn_tokens_dropout = 0.,
disable_abs_pos_emb = None,
use_layerscale = False,
layerscale_init_value = 0.,
unet_skips = False,
integrate_layers = False,
layer_integrate_use_softmax = True,
num_residual_streams = 1,
qkv_receive_diff_residuals = False,
reinject_input = False, # seen first in DEQ paper https://arxiv.org/abs/1909.01377, but later used in a number of papers trying to achieve depthwise generalization https://arxiv.org/abs/2410.03020v1
learned_reinject_input_gate = False,
add_value_residual = False, # resformer from Zhou et al - https://arxiv.org/abs/2410.17897v1 - further corroboration by https://arxiv.org/abs/2412.15113 (faster emergence of ICL) - looks like this setting may becoming a necessity for every transformer soon
learned_value_residual_mix = True, # seeing big improvements when the value residual mix value is learned per token - credit goes to @faresobeid for taking the first step with learned scalar mix, then @Blinkdl for taking it a step further with data dependent. here we will use per token learned
rel_pos_kwargs: dict = dict(),
residual_fn_kwargs: dict = dict(),
**kwargs
):
super().__init__()
rotary_pos_emb = rotary_pos_emb or rotary_xpos
ff_kwargs, kwargs = groupby_prefix_and_trim('ff_', kwargs)
attn_kwargs, kwargs = groupby_prefix_and_trim('attn_', kwargs)
cross_attn_kwargs, kwargs = groupby_prefix_and_trim('cross_attn_', kwargs)
dim_head = attn_kwargs.get('dim_head', DEFAULT_DIM_HEAD)
data_dependent_alibi = attn_kwargs.get('data_dependent_alibi', False)
assert len(kwargs) == 0, f'unrecognized kwargs passed in {kwargs.keys()}'
self.dim = dim
self.causal = causal
self.layers = ModuleList([])
# routing related
# 1. greater than one residual stream, proposed in Hyper-Connections paper https://arxiv.org/abs/2409.19606
# 2. integrating more than one past layer, from LIMe paper https://arxiv.org/abs/2502.09245
qkv_receive_diff_residuals |= integrate_layers # qkv always receives different views if integrating layers
# hyper connections
assert num_residual_streams > 0
has_hyper_connections = num_residual_streams > 1
self.num_residual_streams = num_residual_streams
self.stream_emb = nn.Parameter(torch.zeros(num_residual_streams, dim)) if num_residual_streams > 1 else None
assert not (has_hyper_connections and gate_residual)
hyper_conn_produce_diff_views = qkv_receive_diff_residuals and not integrate_layers
# LIMe
hiddens_counter = 0
self.layer_integrators = ModuleList([])
assert not (qkv_receive_diff_residuals and not (hyper_conn_produce_diff_views or integrate_layers))
# positions related
self.disable_abs_pos_emb = default(disable_abs_pos_emb, (rel_pos_bias or rotary_pos_emb))
rotary_emb_dim = default(rotary_emb_dim, dim_head // 2)
assert rotary_emb_dim <= dim_head, f'rotary emb dim {rotary_emb_dim} must be less than or equal to attention head dimension {dim_head}'
if rotary_emb_dim < 32:
print('when training language model, rotary embedding dimension should be at least 32')
assert not (rotary_xpos and not causal), 'rotary xpos is not compatible with bidirectional attention'
self.rotary_pos_emb = RotaryEmbedding(rotary_emb_dim, use_xpos = rotary_xpos, scale_base = rotary_xpos_scale_base, interpolation_factor = rotary_interpolation_factor, base_rescale_factor = rotary_base_rescale_factor) if rotary_pos_emb else None
assert at_most_one_of(alibi_pos_bias, rel_pos_bias, data_dependent_alibi), 'you can only choose one of Alibi positional bias, data dependent Alibi (forgetting transformers), dynamic tanh, or T5 relative positional bias'
assert rel_pos_num_buckets <= rel_pos_max_distance, 'number of relative position buckets must be less than the relative position max distance'
# relative positional bias
flash_attn = attn_kwargs.get('flash', False)
assert at_most_one_of(rel_pos_bias, dynamic_pos_bias, alibi_pos_bias), 'you can only choose up to one of t5, alibi, or dynamic positional bias'
self.rel_pos = None
if rel_pos_bias:
assert not flash_attn, 'flash attention not compatible with t5 relative positional bias'
self.rel_pos = RelativePositionBias(scale = dim_head ** 0.5, causal = causal, heads = heads, num_buckets = rel_pos_num_buckets, max_distance = rel_pos_max_distance, **rel_pos_kwargs)
elif dynamic_pos_bias:
assert not flash_attn, 'flash attention not compatible with dynamic positional bias'
self.rel_pos = DynamicPositionBias(dim = dim // 4, heads = heads, log_distance = dynamic_pos_bias_log_distance, depth = dynamic_pos_bias_mlp_depth, norm = dynamic_pos_bias_norm, **rel_pos_kwargs)
elif alibi_pos_bias:
alibi_num_heads = default(alibi_num_heads, heads)
assert alibi_num_heads <= heads, 'number of ALiBi heads must be less than the total number of heads'
self.rel_pos = AlibiPositionalBias(heads = alibi_num_heads, total_heads = heads, **rel_pos_kwargs)
assert not (not pre_norm and sandwich_norm), 'sandwich norm cannot be used when not using prenorm'
self.pre_norm = pre_norm
self.sandwich_norm = sandwich_norm
self.residual_attn = residual_attn
self.cross_residual_attn = cross_residual_attn
assert not (flash_attn and (residual_attn or cross_residual_attn)), 'flash attention is not compatible with residual attention'
self.cross_attend = cross_attend
# determine norm
assert at_most_one_of(use_scalenorm, use_rmsnorm, use_dynamic_tanh, use_simple_rmsnorm, use_adaptive_layernorm, use_adaptive_rmsnorm), 'you can only use either scalenorm, rmsnorm, adaptive layernorm, adaptive rmsnorm, or simple rmsnorm'
norm_need_condition = False
dim_condition = default(dim_condition, dim)
dim_condition_mult = 1
if adaptive_condition_mlp:
dim_condition_mult = adaptive_condition_mlp_expansion
if use_scalenorm:
norm_class = ScaleNorm
elif use_rmsnorm:
norm_class = RMSNorm
elif use_simple_rmsnorm:
norm_class = SimpleRMSNorm
elif use_dynamic_tanh:
assert pre_norm, 'dynamic tanh norm only tested for pre-norm'
norm_class = partial(DynamicTanh, init_alpha = dynamic_tanh_init_alpha)
elif use_adaptive_layernorm:
norm_need_condition = True
norm_class = partial(AdaptiveLayerNorm, dim_condition = dim_condition * dim_condition_mult)
elif use_adaptive_rmsnorm:
norm_need_condition = True
norm_class = partial(AdaptiveRMSNorm, dim_condition = dim_condition * dim_condition_mult)
else:
norm_class = LayerNorm
norm_fn = partial(norm_class, dim)
if not norm_need_condition and norm_add_unit_offset:
# researcher Ohad Rubin shares in a blog post by adding an offset to gammas, they can be subjected to weight decay safely
norm_fn = partial(norm_fn, unit_offset = True)
self.norm_need_condition = norm_need_condition
self.dim_condition = dim_condition
# determine default block layer type order
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
# determine post branch wrapper
assert at_most_one_of(use_layerscale, use_adaptive_layerscale)
post_branch_fn = None
post_branch_fn_needs_condition = False
if use_layerscale:
post_branch_fn = partial(LayerScale, dim = dim, init_value = layerscale_init_value)
elif use_adaptive_layerscale:
post_branch_fn = partial(AdaptiveLayerScale, dim = dim, dim_condition = dim_condition * dim_condition_mult)
post_branch_fn_needs_condition = True
self.post_branch_fn_needs_condition = post_branch_fn_needs_condition
if exists(post_branch_fn) and not post_branch_fn_needs_condition and norm_add_unit_offset:
post_branch_fn = partial(post_branch_fn, unit_offset = True)
# setup mlp for conditioning
self.need_condition = norm_need_condition or post_branch_fn_needs_condition
self.adaptive_mlp = nn.Identity()
if self.need_condition and adaptive_condition_mlp:
self.adaptive_mlp = nn.Sequential(
LinearNoBias(dim_condition, dim_condition * dim_condition_mult),
nn.SiLU()
)
# zero init
if zero_init_branch_output:
attn_kwargs = {**attn_kwargs, 'zero_init_output': True}
ff_kwargs = {**ff_kwargs, 'zero_init_output': True}
# setup weight tying, which is a special case of `layer_execute_order`
assert not (exists(layers_execute_order) and exists(custom_layers) and exists(depth)), 'depth should not be passed in if using custom layers and custom layer execution order'
assert not (weight_tie_layers and any([*map(exists, (custom_layers, par_ratio, sandwich_coef))]))
if weight_tie_layers:
assert exists(depth), 'depth must be passed in with `weight_tie_layers` = True'
assert not exists(layers_execute_order)
layers_execute_order = tuple(range(len(default_block))) * depth
depth = 1
# calculate layer block order
len_default_block = 1
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:
assert exists(depth), '`depth` must be passed in for `Decoder` or `Encoder`'
layer_types = default_block * depth
len_default_block = len(default_block)
self.layer_types = layer_types
self.layers_execute_order = default(layers_execute_order, tuple(range(len(layer_types))))
assert all([i < len(self.layer_types) for i in self.layers_execute_order])
self.num_attn_layers = len(list(filter(equals('a'), layer_types)))
# set the depth
depth = default(depth, len(self.layers_execute_order))
self.depth = depth
# stochastic depth
self.layer_dropouts = cast_tuple(layer_dropout, len(layer_types))
# structured dropout for cross attending
self.cross_attn_tokens_dropout = cross_attn_tokens_dropout
# calculate token shifting
shift_tokens = cast_tuple(shift_tokens, len(layer_types))
# optional soft clamping just before the final norm
# used in gemma 2
self.softclamp_output = softclamp_output
self.softclamp_output_value = softclamp_output_value
# whether it has post norm
self.final_norm = norm_fn() if pre_norm else nn.Identity()
# whether unet or not
self.unet_skips = unet_skips
num_skips = self.depth // len_default_block
assert not (unet_skips and num_skips == 0), 'must have depth of at least 2 for unet skip connections'
skip_indices = [i * len_default_block for i in range(num_skips)]
self.skip_combines = ModuleList([])
# whether there is reinjection of input at every layer
self.reinject_input = reinject_input
self.reinject_input_proj = nn.Linear(dim, dim, bias = False) if reinject_input else None
self.learned_reinject_input_gate = nn.Linear(dim, 1, bias = False) if learned_reinject_input_gate else None
# add the value from the first self attention block to all latter projected self attention values as a residual
self.add_value_residual = add_value_residual
is_first_self_attn = True
is_first_cross_attn = True
learned_value_residual_mix &= add_value_residual
# iterate and construct layers
for ind, (layer_type, layer_shift_tokens) in enumerate(zip(self.layer_types, shift_tokens)):
# `ind` is the index of each module - attention, feedforward, cross attention
# but `block_ind` refers to the typical enumeration of a transformer block (attn + ff + [optional] cross attn)
block_begin = divisible_by(ind, len_default_block)
block_ind = ind // len_default_block
is_last_layer = ind == (len(self.layer_types) - 1)
# attention, cross attention, feedforward
layer_qkv_receives_diff_view = layer_type == 'a' and qkv_receive_diff_residuals and not (is_first_self_attn and integrate_layers)
if layer_type == 'a':
self_attn_learned_value_residual = learned_value_residual_mix and not is_first_self_attn
layer = Attention(dim, heads = heads, causal = causal, qkv_receive_diff_residuals = layer_qkv_receives_diff_view, learned_value_residual_mix = self_attn_learned_value_residual, rotate_num_heads = rotate_num_heads, **attn_kwargs)
is_first_self_attn = False
elif layer_type == 'c':
layer = Attention(dim, heads = heads, **{**attn_kwargs, **cross_attn_kwargs})
is_first_cross_attn = False
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 layer_shift_tokens > 0:
shift_range_upper = layer_shift_tokens + 1
shift_range_lower = -layer_shift_tokens if not causal else 0
layer = ShiftTokens(range(shift_range_lower, shift_range_upper), layer)
if exists(post_branch_fn):
layer = post_branch_fn(layer)
layer_integrate = None
if integrate_layers:
num_layer_hiddens = ind + 1
layer_integrate_num_view = 3 if layer_qkv_receives_diff_view else 1
layer_integrate = DynamicLIMe(dim, num_layer_hiddens, num_views = layer_integrate_num_view, use_softmax = layer_integrate_use_softmax)
if has_hyper_connections:
residual_fn = partial(HyperConnection, num_residual_streams = num_residual_streams)
if layer_type == 'a' and hyper_conn_produce_diff_views:
residual_fn = partial(residual_fn, num_input_views = 3)
elif gate_residual:
residual_fn = GRUGating
else:
residual_fn = Residual
residual = residual_fn(dim, layer_index = ind, scale_residual = scale_residual, scale_residual_constant = scale_residual_constant, **residual_fn_kwargs)
# handle unet skip connection
skip_combine = None
is_latter_half = block_begin and block_ind >= (self.depth / 2)
if self.unet_skips and is_latter_half:
skip_combine = ConcatCombine(dim, skip_indices.pop())
# all normalizations of the layer
pre_branch_norm = norm_fn() if pre_norm else None
post_branch_norm = norm_fn() if sandwich_norm else None
post_main_norm = norm_fn() if not pre_norm else None
norms = ModuleList([
pre_branch_norm,
post_branch_norm,
post_main_norm
])
self.skip_combines.append(skip_combine)
self.layer_integrators.append(layer_integrate)
self.layers.append(ModuleList([
norms,
layer,
residual
]))
# determine whether can cache kv
self.can_cache_kv = all([module.can_cache_kv for module in self.modules() if isinstance(module, Attention)])
def forward(
self,
x,
context = None,
mask = None,
context_mask = None,
attn_mask = None,
self_attn_kv_mask = None,
mems = None,
mem_masks = None,
seq_start_pos: Tensor | None = None,
cache: LayerIntermediates | None = None,
cache_age = 1,
return_hiddens = False,
rotary_pos_emb = None,
pos = None,
context_pos = None,
attn_bias = None,
condition = None,
in_attn_cond = None, # https://arxiv.org/abs/2105.04090
layers_execute_order: tuple[int, ...] | None = None
):
assert not (self.cross_attend ^ exists(context)), 'context must be passed in if cross_attend is set to True'
assert not (exists(condition) ^ self.need_condition), 'condition needs to be passed in if using adaptive layernorm or vice versa'
# handle condition
if exists(condition):
assert condition.shape[-1] == self.dim_condition, f'expected condition dimension of {self.dim_condition} but received {condition.shape[-1]}'
assert condition.ndim in {2, 3}
if condition.ndim == 2:
condition = rearrange(condition, 'b d -> b 1 d')
condition = self.adaptive_mlp(condition)
# setup maybe layernorm kwarg
norm_kwargs = dict()
if self.norm_need_condition:
norm_kwargs.update(condition = condition)
# maybe post branch fn conditioning (DiT paper's ada-ln-zero)
block_forward_kwargs = dict()
if self.post_branch_fn_needs_condition:
block_forward_kwargs.update(condition = condition)
# initialize accums
hiddens = []
layer_hiddens = []
intermediates = []
prev_attn = None
prev_cross_attn = None
mems = mems.copy() if exists(mems) else [None] * self.num_attn_layers
mem_masks = mem_masks.copy() if exists(mem_masks) else [None] * self.num_attn_layers
# handle left padded sequences
if exists(seq_start_pos):
seq_arange = arange(x.shape[-2], device = x.device, dtype = torch.long)
left_pad_mask = seq_arange >= seq_start_pos[..., None]
if exists(self_attn_kv_mask):
self_attn_kv_mask = self_attn_kv_mask & left_pad_mask
else:
self_attn_kv_mask = left_pad_mask
# rotary positions
cross_attn_rotary_pos_emb = dict()
if exists(self.rotary_pos_emb):
if not exists(rotary_pos_emb):
maybe_mem = first(mems, None) # todo - handle edge case where different layers get different memory lengths. don't think this will ever come up but who knows
mem_len = maybe_mem.shape[1] if exists(maybe_mem) else 0
if not exists(pos):
pos = arange(x.shape[1] + mem_len, device = x.device) - mem_len
rotary_pos_emb = self.rotary_pos_emb(pos)
# allow for rotary positions for context if provided
if exists(context_pos):
assert self.cross_attend
context_rotary_pos_emb = self.rotary_pos_emb(context_pos)
cross_attn_rotary_pos_emb.update(
rotary_pos_emb = rotary_pos_emb,
context_rotary_pos_emb = context_rotary_pos_emb
)
# assume cached key / values
attn_cache = []
if exists(cache):
assert self.causal and not any([*map(exists, (mask, attn_mask))])
if exists(context):
context = context[:, :0]
if cache_age > 0:
x = x[:, -cache_age:] # for spec decoding, may be greater than 1
attn_cache = cache.attn_intermediates
iter_attn_cache = iter(attn_cache)
# setup multistreams if needed
streams = self.num_residual_streams
is_multistream = streams > 1
if is_multistream:
x = einx.add('b n d, s d -> (b s) n d', x, self.stream_emb)
# get layers to be executed
layer_variables = (
self.layer_types,
self.skip_combines,
self.layers,
self.layer_dropouts,
self.layer_integrators
)
# able to override the layers execution order on forward, for trying to depth extrapolate
layers_execute_order = default(layers_execute_order, self.layers_execute_order)
layer_variables = tuple(tuple(layer_variable[i] for i in layers_execute_order) for layer_variable in layer_variables)
# derived input for reinjection if needed
inp_inject = None
if self.reinject_input:
assert not exists(in_attn_cond)
inp_inject = self.reinject_input_proj(x)
elif exists(in_attn_cond):
# handle in-attention conditioning, which serves the same purpose of having the network learn the residual
inp_inject = in_attn_cond if in_attn_cond.ndim == 3 else rearrange(in_attn_cond, 'b d -> b 1 d')
if exists(inp_inject) and exists(self.learned_reinject_input_gate):
inp_inject_gate = self.learned_reinject_input_gate(x).sigmoid()
inp_inject = inp_inject * inp_inject_gate
# store all hiddens for skips
skip_hiddens = []
# for value residuals
first_self_attn_inter = None
first_cross_attn_inter = None
# go through the attention and feedforward layers
for ind, (layer_type, skip_combine, (norm, block, residual_fn), layer_dropout, layer_integrator) in enumerate(zip(*layer_variables)):
is_last = ind == (len(self.layers) - 1)
# handle skip connections
skip_hiddens.append(x)
if exists(skip_combine):
x = skip_combine(x, skip_hiddens)
# layer dropout
if self.training and layer_dropout > 0. and random() < layer_dropout:
continue
if layer_type == 'a':
if return_hiddens:
hiddens.append(x)
layer_mem = mems.pop(0) if mems else None
layer_mem_mask = mem_masks.pop(0) if mem_masks else None
if layer_type == 'c':
if self.training and self.cross_attn_tokens_dropout > 0.:
context, context_mask = dropout_seq(context, context_mask, self.cross_attn_tokens_dropout)
x, inner_residual, residual_kwargs = residual_fn.prepare(x)
layer_hiddens.append(x)
if exists(layer_integrator):
x = layer_integrator(x, layer_hiddens)
pre_norm, post_branch_norm, post_main_norm = norm
if self.need_condition:
pre_norm = maybe(partial)(pre_norm, **norm_kwargs)
post_branch_norm = maybe(partial)(post_branch_norm, **norm_kwargs)
post_main_norm = maybe(partial)(post_main_norm, **norm_kwargs)
if exists(inp_inject):
x = x + inp_inject
if exists(pre_norm):
x = pre_norm(x)
if layer_type == 'a' and exists(layer_mem):
layer_mem = pre_norm(layer_mem)
block = partial(block, **block_forward_kwargs)
# handle maybe value residuals
maybe_self_attn_value_residual = None
maybe_cross_attn_value_residual = None
if self.add_value_residual:
if exists(first_self_attn_inter):
maybe_self_attn_value_residual = first_self_attn_inter.values
if exists(first_cross_attn_inter):
maybe_cross_attn_value_residual = first_cross_attn_inter.values
# forward depending on layer type
if layer_type == 'a':
out, inter = block(x, mask = mask, context_mask = self_attn_kv_mask, attn_mask = attn_mask, rel_pos = self.rel_pos, pos = pos, rotary_pos_emb = rotary_pos_emb, prev_attn = prev_attn, cache = next(iter_attn_cache, None), mem = layer_mem, mem_mask = layer_mem_mask, attn_bias = attn_bias, value_residual = maybe_self_attn_value_residual, return_intermediates = True)
elif layer_type == 'c':
out, inter = block(x, context = context, mask = mask, context_mask = context_mask, prev_attn = prev_cross_attn, cache = next(iter_attn_cache, None), value_residual = maybe_cross_attn_value_residual, **cross_attn_rotary_pos_emb, return_intermediates = True)
elif layer_type == 'f':
out = block(x)
# store first self or cross attention intermediate for value residual
if not exists(first_self_attn_inter) and layer_type == 'a':
first_self_attn_inter = inter
if not exists(first_cross_attn_inter) and layer_type == 'c':
first_cross_attn_inter = inter
if exists(post_branch_norm):
out = post_branch_norm(out)
x = residual_fn(out, inner_residual, **residual_kwargs)
if layer_type in ('a', 'c') and return_hiddens:
inter.layer_type = layer_type
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 exists(post_main_norm):
x = post_main_norm(x)
if return_hiddens:
layer_hiddens.append(x)
if self.softclamp_output:
x = softclamp(x, self.softclamp_output_value)
final_norm = self.final_norm
if self.need_condition:
final_norm = maybe(partial)(final_norm, **norm_kwargs)
# take care of multistreams if needed, use sum for now
if is_multistream:
x = reduce(x, '(b s) n d -> b n d', 'sum', s = streams)
x = final_norm(x)
if not return_hiddens:
return x
intermediates = LayerIntermediates(
hiddens = hiddens,
last_hidden = x,
attn_intermediates = intermediates,
layer_hiddens = layer_hiddens,
)
return x, intermediates
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 PrefixDecoder(AttentionLayers):
def __init__(self, **kwargs):
assert 'causal' not in kwargs, 'cannot set causality on decoder'
super().__init__(causal = False, **kwargs)
def forward(
self,
x,
*args,
attn_mask = None,
prefix_attn_len = None,
**kwargs
):
b, n, device = x.shape[0], x.shape[1], x.device
causal_mask = torch.ones((n, n), device = device, dtype = torch.bool).triu(1)
forwarded_mask = ~causal_mask
if exists(prefix_attn_len):
if isinstance(prefix_attn_len, int):
prefix_attn_len = torch.full((b,), prefix_attn_len, device = device)
prefix_mask = arange(n, device = device) < rearrange(prefix_attn_len, 'b -> b 1 1 1')
forwarded_mask = forwarded_mask | prefix_mask
if exists(attn_mask):
forwarded_mask = forwarded_mask & attn_mask
return super().forward(x, *args, attn_mask = forwarded_mask, **kwargs)
class CrossAttender(AttentionLayers):
def __init__(self, **kwargs):
super().__init__(cross_attend = True, only_cross = True, **kwargs)
class ViTransformerWrapper(Module):
def __init__(
self,
*,
image_size,
patch_size,
attn_layers: Encoder,
channels = 3,
num_classes = None,
post_emb_norm = False,
num_register_tokens = 0,
emb_dropout = 0.
):
super().__init__()
assert divisible_by(image_size, patch_size), 'image dimensions must be divisible by the patch size'
dim = attn_layers.dim
num_patches = (image_size // patch_size) ** 2
patch_dim = channels * patch_size ** 2
self.patch_size = patch_size
self.pos_embedding = nn.Parameter(torch.randn(1, num_patches, dim))
has_register_tokens = num_register_tokens > 0
self.has_register_tokens = has_register_tokens
if has_register_tokens:
self.register_tokens = nn.Parameter(torch.randn(num_register_tokens, dim))
self.patch_to_embedding = nn.Sequential(
LayerNorm(patch_dim),
nn.Linear(patch_dim, dim),
LayerNorm(dim)
)
self.post_emb_norm = LayerNorm(dim) if post_emb_norm else nn.Identity()
self.dropout = nn.Dropout(emb_dropout)
self.attn_layers = attn_layers
self.mlp_head = nn.Linear(dim, num_classes) if exists(num_classes) else nn.Identity()
def forward(
self,
img,
return_embeddings = False,
return_logits_and_embeddings = False
):
b, p = img.shape[0], 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)
n = x.shape[1]
x = x + self.pos_embedding[:, :n]
x = self.post_emb_norm(x)
x = self.dropout(x)
if self.has_register_tokens:
r = repeat(self.register_tokens, 'n d -> b n d', b = b)
x, ps = pack((x, r), 'b * d')
embed = self.attn_layers(x)
if self.has_register_tokens:
embed, _ = unpack(embed, ps, 'b * d')
assert at_most_one_of(return_embeddings, return_logits_and_embeddings)
if not exists(self.mlp_head) or return_embeddings:
return embed
pooled = embed.mean(dim = -2)
logits = self.mlp_head(pooled)
if not return_logits_and_embeddings:
return logits
return logits, embed
class TransformerWrapper(Module):
def __init__(
self,
*,
num_tokens,
max_seq_len,
attn_layers: AttentionLayers,
embed_num_tokens: dict[str, int] = dict(),
emb_dim = None,
max_mem_len = 0,
shift_mem_down = 0,
emb_dropout = 0.,
post_emb_norm = False,
num_memory_tokens = None,
memory_tokens_interspersed_every = None,
tie_embedding = False,
logits_dim = None,
return_only_embed = False,
num_output_heads = 1,
use_abs_pos_emb = True,
scaled_sinu_pos_emb = False,
l2norm_embed = False,
recycling = False, # from Jumper et al. - Alphafold2
train_max_recycle_steps = 4, # saw a benefit for language modeling up to 3 recycling steps, so let's default this to 4
emb_frac_gradient = 1., # GLM-130B and Cogview successfully used this, set at 0.1
attn_z_loss_weight = 1e-4,
average_pool_embed = False,
use_cls_token = False,
num_cls_tokens = 1,
squeeze_out_last_dim = False,
token_emb: TokenEmbedding | None = None,
mixture_of_softmax = False,
mixture_of_softmax_k = 4,
sigsoftmax_logits = False,
to_logits: Module | None = None,
):
super().__init__()
dim = attn_layers.dim
emb_dim = default(emb_dim, dim)
self.emb_dim = emb_dim
self.num_tokens = num_tokens
self.num_cls_tokens = num_cls_tokens
self.max_seq_len = max_seq_len
self.max_mem_len = max_mem_len
self.shift_mem_down = shift_mem_down
self.l2norm_embed = l2norm_embed
if not exists(token_emb):
token_emb = TokenEmbedding(emb_dim, num_tokens, l2norm_embed = l2norm_embed)
self.token_emb = token_emb
no_abs_pos_emb = max_seq_len == 0 or not (use_abs_pos_emb and not attn_layers.disable_abs_pos_emb)
if no_abs_pos_emb:
self.pos_emb = always(0)
elif scaled_sinu_pos_emb:
self.pos_emb = ScaledSinusoidalEmbedding(emb_dim)
else:
self.pos_emb = AbsolutePositionalEmbedding(emb_dim, max_seq_len, l2norm_embed = l2norm_embed)
# additional embeddings - say type embedding from BERT
self.embeds = None
if len(embed_num_tokens) > 0:
self.embeds = ModuleDict({f'{name}_embed': nn.Embedding(num_tokens, emb_dim) for name, num_tokens in embed_num_tokens.items()})
# fraction of the gradient that should go to the embedding, https://arxiv.org/abs/2105.13290
self.emb_frac_gradient = emb_frac_gradient
self.post_emb_norm = LayerNorm(emb_dim) if post_emb_norm else nn.Identity()
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.init_()
assert num_output_heads > 0
assert at_most_one_of(average_pool_embed, use_cls_token)
# maybe recycling
self.recycling = recycling
self.recycled_proj = LinearNoBias(dim, dim) if recycling else None
self.train_max_recycle_steps = train_max_recycle_steps
# classic cls token from the bert days
self.cls_token = None
if use_cls_token:
self.cls_token = nn.Parameter(torch.zeros(num_cls_tokens, dim))
nn.init.normal_(self.cls_token, std = 0.02)
# whether to average pool the embed (`global average pool`)
self.average_pool_embed = average_pool_embed
# output type
self.output_is_log_prob = mixture_of_softmax
self.to_mixture = None
self.combine_mixture = None
if mixture_of_softmax:
assert num_output_heads == 1
self.to_mixture = Sequential(
LinearNoBias(dim, dim * mixture_of_softmax_k),
Rearrange('... (k d) -> ... k d', k = mixture_of_softmax_k)
)
self.combine_mixture = LinearNoBias(dim, mixture_of_softmax_k)
# sig softmax
self.sigsoftmax_logits = sigsoftmax_logits
# output head, usually to logits of num_tokens
logits_dim = default(logits_dim, num_tokens)
self.has_multiple_heads = num_output_heads > 1
if return_only_embed:
self.to_logits = None
elif tie_embedding:
assert isinstance(token_emb, TokenEmbedding), 'can only tie embedding if using `TokenEmbedding`'
self.to_logits = lambda t: t @ self.token_emb.emb.weight.t()
elif num_output_heads > 1:
self.to_logits = ModuleList([LinearNoBias(dim, logits_dim) for _ in range(num_output_heads)])
else:
self.to_logits = LinearNoBias(dim, logits_dim) if not exists(to_logits) else to_logits
# 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))
self.memory_tokens_interspersed_every = memory_tokens_interspersed_every
# squeeze out last dimension if possible
self.squeeze_out_last_dim = squeeze_out_last_dim
# whether can do cached kv decoding
self.can_cache_kv = self.num_memory_tokens == 0 and not recycling and self.attn_layers.can_cache_kv
self.can_cache_kv_outside_max_seq_len = no_abs_pos_emb
def init_(self):
if hasattr(self.token_emb, 'init_'):
self.token_emb.init_()
if self.l2norm_embed:
if not isinstance(self.pos_emb, always):
nn.init.normal_(self.pos_emb.emb.weight, std = 1e-5)
def forward(
self,
x,
return_embeddings = False,
return_logits_and_embeddings = False,
return_intermediates = False,
return_embeddings_and_intermediates = False,
return_logit_entropies = False,
mask = None,
return_mems = False,
return_attn = False,
mems = None,
mem_masks = None,
recycle_steps = None,
pos = None,
prepend_embeds = None,
prepend_mask = None,
embed_ids: dict[str, Tensor] = dict(),
sum_embeds = None,
return_attn_z_loss = False,
attn_z_loss_weight = 1e-4,
seq_start_pos = None,
cache: LayerIntermediates | None = None,
token_emb_kwargs = dict(),
to_logits_kwargs = dict(),
**kwargs,
):
# if sequence is None, auto create an empty one if `prepend_embeds` was supplied
if not exists(x):
assert exists(prepend_embeds)
x = prepend_embeds.new_empty((prepend_embeds.shape[0], 0), dtype = torch.long)
# shapes and variables
b, n, device, num_mems, has_memory_tokens, emb_frac_gradient, orig_mask = x.shape[0], x.shape[1], x.device, self.num_memory_tokens, self.num_memory_tokens > 0, self.emb_frac_gradient, mask
return_hiddens = return_mems | return_attn | return_intermediates | return_attn_z_loss | return_embeddings_and_intermediates
return_embeddings = return_embeddings | (not exists(self.to_logits)) | return_embeddings_and_intermediates
# absolute positional embedding
external_pos_emb = exists(pos) and pos.dtype != torch.long
pos_emb = self.pos_emb(x, pos = pos, seq_start_pos = seq_start_pos) if not external_pos_emb else pos
x = self.token_emb(x, **token_emb_kwargs) + pos_emb
# add additional embeddings
assert not (exists(self.embeds) ^ (len(embed_ids) > 0)), '`embed_num_tokens` must be defined on `TransformerWrapper`'
if exists(self.embeds):
assert len(embed_ids) == len(self.embeds)
for name, embed_id in embed_ids.items():
embed_key = f'{name}_embed'
assert embed_key in self.embeds
embed = self.embeds[embed_key](embed_id)
x = x + embed
# for summing embeddings passed externally - needs this for self-conditioning in non-autoregressive training
if exists(sum_embeds):
x = x + sum_embeds
# post embedding norm, purportedly leads to greater stabilization
x = self.post_emb_norm(x)
# whether to append embeds, as in PaLI, for image embeddings
if exists(prepend_embeds):
prepend_seq, prepend_dim = prepend_embeds.shape[1:]
assert prepend_dim == x.shape[-1], 'prepended embeddings need to have same dimensions as text model dimensions'
x = cat((prepend_embeds, x), dim = -2)
if exists(prepend_mask) or exists(mask):
mask = default(mask, lambda: torch.ones((b, n), device = device, dtype = torch.bool))
prepend_mask = default(prepend_mask, lambda: torch.ones((b, prepend_seq), device = device, dtype = torch.bool))
mask = cat((prepend_mask, mask), dim = -1)
# whether to reduce the gradient going to the embedding, from cogview paper, corroborated by GLM-130B model
if emb_frac_gradient < 1:
assert emb_frac_gradient > 0
x = x * emb_frac_gradient + x.detach() * (1 - emb_frac_gradient)
# embedding dropout
x = self.emb_dropout(x)
x = self.project_emb(x)
# maybe cls token
if exists(self.cls_token):
cls_tokens = repeat(self.cls_token, '... -> b ...', b = b)
x, cls_packed_shape = pack([cls_tokens, x], 'b * d')
if exists(mask):
mask = F.pad(mask, (self.num_cls_tokens, 0), value = True)
# maybe memory / register tokens
if has_memory_tokens:
mem_seq = x.shape[-2]
mem_every = self.memory_tokens_interspersed_every
if exists(mem_every):
assert mem_every > 0
assert isinstance(self.attn_layers, Decoder), 'only for decoder'
next_seq_len = math.ceil(n / mem_every) * mem_every
x = pad_at_dim(x, (0, next_seq_len - n), dim = -2, value = 0.)
x = rearrange(x, 'b (n m) d -> (b n) m d', m = mem_every)
mem = repeat(self.memory_tokens, 'n d -> b n d', b = x.shape[0])
x, mem_packed_shape = pack((mem, x), 'b * d')
# auto-handle masking after appending memory tokens
if not exists(mem_every) and exists(mask):
mask = pad_at_dim(mask, (num_mems, 0), dim = -1, value = True)
if exists(mem_every):
x = rearrange(x, '(b n) m d -> b (n m) d', b = b)
# handle maybe shifting of memories
if self.shift_mem_down and exists(mems):
mems_l, mems_r = mems[:self.shift_mem_down], mems[self.shift_mem_down:]
mems = [*mems_r, *mems_l]
# attention layers
if not self.recycling:
assert not exists(recycle_steps) or recycle_steps == 1, 'you did not train with recycling'
# regular
attended, intermediates = self.attn_layers(x, mask = mask, mems = mems, mem_masks = mem_masks, cache = cache, return_hiddens = True, seq_start_pos = seq_start_pos, **kwargs)
else:
# recycling
recycle_steps = default(recycle_steps, (randrange(self.train_max_recycle_steps) + 1) if self.training else None)
assert exists(recycle_steps) and recycle_steps > 0, '`recycle_steps` must be provided on forward if recycling is turned on and not training'
for i in range(recycle_steps):
first_step = i == 0
last_step = i == (recycle_steps - 1)
context = nullcontext if last_step else torch.no_grad
with context():
maybe_recycled = self.recycled_proj(attended.detach()) if not first_step else 0.
attended, intermediates = self.attn_layers(x + maybe_recycled, mask = mask, mems = mems, mem_masks = mem_masks, cache = cache, return_hiddens = True, seq_start_pos = seq_start_pos, **kwargs)
x = attended
# handle memories post-attention
if has_memory_tokens:
if exists(mem_every):
x = rearrange(x, 'b (n m) d -> (b n) m d', m = (mem_every + num_mems))
mem, x = unpack(x, mem_packed_shape, 'b * d')
intermediates.memory_tokens = mem
if exists(mem_every):
x = rearrange(x, '(b n) m d -> b (n m) d', b = b)
x = x[:, :mem_seq]
# global average pool
if self.average_pool_embed:
x = masked_mean(x, mask = orig_mask, dim = 1)
if exists(self.cls_token):
x, _ = unpack(x, cls_packed_shape, 'b * d')
x = x.squeeze(1) # Remove sequence dimension if num_cls_tokens=1 to keep previous behavior
# handle expansion to mixture if needed (for mixture of softmax)
combine_mixture = None
if exists(self.to_mixture):
combine_mixture = self.combine_mixture(x).softmax(dim = -1)
x = self.to_mixture(x)
# projecting to logits
if not return_embeddings:
if self.has_multiple_heads:
logits = tuple(fn(x, **to_logits_kwargs) for fn in self.to_logits)
else:
logits = self.to_logits(x, **to_logits_kwargs)
# maybe sig softmax
if self.sigsoftmax_logits:
logits = logits + logits.sigmoid().log()
# handle maybe combine mixture
if exists(combine_mixture):
with autocast('cuda', enabled = False):
prob = logits.softmax(dim = -1)
mos = einsum('... k d, ... k -> ... d', prob, combine_mixture)
logits = log(mos)
# maybe squeeze out last dimension of logits
if self.squeeze_out_last_dim:
logits = tuple((rearrange(t, '... 1 -> ...') if t.shape[-1] == 1 else t) for t in cast_tuple(logits))
if not self.has_multiple_heads:
logits = first(logits)
# different returns
if return_logits_and_embeddings:
out = (logits, x)
elif return_embeddings_and_intermediates:
out = (x, intermediates)
elif return_embeddings:
out = x
else:
out = logits
# logit entropies
if return_logit_entropies:
intermediates.logit_entropies = calc_entropy(logits)
return_intermediates = True
# aux loss
if return_attn_z_loss:
pre_softmax_attns = [t.pre_softmax_attn for t in intermediates.attn_intermediates]
intermediates.attn_z_loss = calc_z_loss(pre_softmax_attns, weight = attn_z_loss_weight)
return_intermediates = True
if return_mems:
hiddens = intermediates.hiddens
new_mems = [cat(pair, dim = -2) for pair in zip(mems, hiddens)] if exists(mems) else hiddens
new_mems = [t[..., -self.max_mem_len:, :].detach() for t in new_mems]
if not return_intermediates:
return out, new_mems
intermediates.mems = new_mems
if return_intermediates:
return out, intermediates
if return_attn:
attn_maps = [t.post_softmax_attn for t in intermediates.attn_intermediates]
return out, attn_maps
return out
class XTransformer(Module):
def __init__(
self,
*,
dim,
tie_token_emb = False,
ignore_index = -100,
pad_value = 0,
cross_attn_tokens_dropout = 0.,
**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['emb_dropout'] = enc_kwargs.pop('emb_dropout', 0)
enc_transformer_kwargs['num_memory_tokens'] = enc_kwargs.pop('num_memory_tokens', None)
enc_transformer_kwargs['scaled_sinu_pos_emb'] = enc_kwargs.pop('scaled_sinu_pos_emb', False)
enc_transformer_kwargs['use_abs_pos_emb'] = enc_kwargs.pop('use_abs_pos_emb', True)
dec_transformer_kwargs = pick_and_pop(['num_tokens', 'max_seq_len'], dec_kwargs)
dec_transformer_kwargs['emb_dropout'] = dec_kwargs.pop('emb_dropout', 0)
dec_transformer_kwargs['scaled_sinu_pos_emb'] = dec_kwargs.pop('scaled_sinu_pos_emb', False)
dec_transformer_kwargs['use_abs_pos_emb'] = dec_kwargs.pop('use_abs_pos_emb', True)
self.cross_attn_tokens_dropout = cross_attn_tokens_dropout # how many tokens from the encoder to dropout when cross attending from decoder - seen in a couple papers, including Perceiver AR - this will also be very effective regularization when cross attending to very long memories
self.encoder = TransformerWrapper(
**enc_transformer_kwargs,
return_only_embed = True,
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, ignore_index=ignore_index, pad_value=pad_value)
@torch.no_grad()
def generate(self, seq_in, seq_out_start, seq_len, mask = None, attn_mask = None, **kwargs):
encodings = self.encoder(seq_in, mask = mask, attn_mask = attn_mask, return_embeddings = True)
return self.decoder.generate(seq_out_start, seq_len, context = encodings, context_mask = mask, **kwargs)
def forward(self, src, tgt, mask = None, attn_mask = None, src_prepend_embeds = None):
enc = self.encoder(src, mask = mask, attn_mask = attn_mask, prepend_embeds = src_prepend_embeds, return_embeddings = True)
if exists(src_prepend_embeds) and exists(mask):
mask = pad_at_dim(mask, (src_prepend_embeds.shape[-2], 0), dim = -1, value = True)
if self.training and self.cross_attn_tokens_dropout > 0:
enc, mask = dropout_seq(enc, mask, self.cross_attn_tokens_dropout)
out = self.decoder(tgt, context = enc, context_mask = mask)
return out
#=================================================================================================================================
# autoregressive_wrapper.py
#=================================================================================================================================
from math import ceil, log
from typing import Tuple, Callable
import torch
from torch import nn, Tensor
from torch.nn import Module
import torch.nn.functional as F
from einops import rearrange, pack, unpack
def exists(val):
return val is not None
def default(val, d):
return val if exists(val) else d
def identity(t, *args, **kwargs):
return t
def join(arr, delimiter = ', '):
return delimiter.join(arr)
def cast_tuple(t, length = 1):
return t if isinstance(t, tuple) else (t,) * length
def eval_decorator(fn):
def inner(self, *args, **kwargs):
was_training = self.training
self.eval()
out = fn(self, *args, **kwargs)
self.train(was_training)
return out
return inner
# for variable lengthed prefixes
def align_right(t, lens, pad_id = 0):
batch, seq_len, device, dtype = *t.shape, t.device, t.dtype
assert lens.ndim == 1 and lens.shape[0] == batch
assert lens.amax() <= seq_len
pad_lens = seq_len - lens
max_pad_len = pad_lens.amax()
batch_arange = torch.arange(batch, device = device, dtype = torch.long)[..., None]
prompt_len_arange = torch.arange(seq_len, device = device, dtype = torch.long)
t = F.pad(t, (max_pad_len, 0), value = pad_id)
offset = max_pad_len - pad_lens
aligned = t[batch_arange, prompt_len_arange + offset[..., None]]
return aligned
# nucleus
def top_p(logits, thres = 0.9):
sorted_logits, sorted_indices = torch.sort(logits, descending = True)
cum_probs = torch.cumsum(F.softmax(sorted_logits, dim = -1), dim = -1)
sorted_indices_to_remove = cum_probs > thres
sorted_indices_to_remove = F.pad(sorted_indices_to_remove, (1, -1), value = False)
sorted_logits[sorted_indices_to_remove] = float('-inf')
return sorted_logits.scatter(1, sorted_indices, sorted_logits)
# topk
def top_k(logits, frac_num_tokens = 0.1, k = None):
num_tokens = logits.shape[-1]
k = default(k, ceil(frac_num_tokens * num_tokens))
k = min(k, num_tokens)
val, ind = torch.topk(logits, k)
probs = torch.full_like(logits, float('-inf'))
probs.scatter_(1, ind, val)
return probs
# top_a
def top_a(logits, min_p_pow = 2.0, min_p_ratio = 0.02):
probs = logits.softmax(dim = -1)
max_probs = probs.amax(dim = -1, keepdim = True)
limit = torch.pow(max_probs, min_p_pow) * min_p_ratio
return torch.where(probs < limit, float('-inf'), logits)
# min_p
# https://arxiv.org/abs/2407.01082
def min_p(logits, min_p = 0.1):
probs = logits.softmax(dim = -1)
max_probs = probs.amax(dim = -1, keepdim = True)
limit = min_p * max_probs
return torch.where(probs < limit, float('-inf'), logits)
# filter logits functions dict[str -> Callable]
FILTER_LOGITS_FN = dict(
top_p = top_p,
top_k = top_k,
top_a = top_a,
min_p = min_p
)
# contrastive decoding function
def contrastive_decode_fn(
expert_logits,
amateur_logits,
alpha = 0.1,
beta = 0.5
):
"""
Appendix A Algorithm 2
https://arxiv.org/abs/2309.09117
"""
cutoff = log(alpha) + expert_logits.amax(dim = -1, keepdim = True)
diffs = (1 + beta) * expert_logits - beta * amateur_logits
contrastive_decode_logits = diffs.masked_fill(expert_logits < cutoff, -torch.finfo(expert_logits.dtype).max)
return contrastive_decode_logits
# autoregressive wrapper class
class AutoregressiveWrapper(Module):
def __init__(
self,
net,
ignore_index = -100,
pad_value = 0,
mask_prob = 0.,
add_attn_z_loss = False
):
super().__init__()
self.pad_value = pad_value
self.ignore_index = ignore_index
self.net = net
self.max_seq_len = net.max_seq_len
# paper shows masking (MLM) in conjunction with autoregressive decoder-only training leads to big improvements https://arxiv.org/abs/2210.13432
assert mask_prob < 1.
self.mask_prob = mask_prob
# whether to add router z-loss
self.add_attn_z_loss = add_attn_z_loss
@torch.no_grad()
@eval_decorator
def generate(
self,
prompts,
seq_len,
eos_token = None,
temperature = 1.,
prompt_lens: Tensor | None = None,
filter_logits_fn: str | Callable = top_k,
restrict_to_max_seq_len = True,
amateur_model: Module | Tuple[Module] | None = None,
filter_kwargs: dict = dict(),
contrastive_decode_kwargs: dict | Tuple[dict] = dict(
beta = 0.5,
alpha = 0.1
),
cache_kv = True,
return_prime=False,
verbose=True,
**kwargs
):
max_seq_len, greedy, device = self.max_seq_len, temperature == 0., prompts.device
prompts, ps = pack([prompts], '* n')
b, t = prompts.shape
# handle filter logits fn given as string
if isinstance(filter_logits_fn, str):
assert filter_logits_fn in FILTER_LOGITS_FN, f"only {join(FILTER_LOGITS_FN.keys())} are available"
filter_logits_fn = FILTER_LOGITS_FN[filter_logits_fn]
# handle variable lengthed prompts (prefixes)
seq_start_pos = None
if exists(prompt_lens):
prompts = align_right(prompts, prompt_lens, pad_id = self.pad_value)
seq_start_pos = t - prompt_lens
# output from which sampled tokens appended to
out = prompts
if verbose:
print("Generating sequence of max length:", seq_len)
# kv caches
cache = None
# if doing contrastive decoding, turn off filter automatically
if exists(amateur_model):
amateur_model = cast_tuple(amateur_model)
contrastive_decode_kwargs = cast_tuple(contrastive_decode_kwargs)
assert len(amateur_model) == len(contrastive_decode_kwargs)
amateur_caches = [None] * len(amateur_model)
filter_logits_fn = identity
for i, module in enumerate(amateur_model):
if isinstance(module, AutoregressiveWrapper):
amateur_model[i] = module.net
module.eval()
# sampling up to seq_len
for sl in range(seq_len):
if restrict_to_max_seq_len:
max_len_exceeded = out.shape[-1] > max_seq_len
assert not (cache_kv and max_len_exceeded and not self.net.can_cache_kv_outside_max_seq_len), 'the network cannot use cached key values when decoding outside the max sequence length. most likely because you are using absolute positional embedding. you can switch to rotary embeddings to resolve this issue'
x = out[:, -max_seq_len:]
if exists(cache):
for inter in cache.attn_intermediates:
if inter.layer_type == 'a':
inter.cached_kv = [t[..., -(max_seq_len - 1):, :] for t in inter.cached_kv]
logits, new_cache = self.net(
x,
return_intermediates = True,
cache = cache,
seq_start_pos = seq_start_pos,
**kwargs
)
if cache_kv and self.net.can_cache_kv:
cache = new_cache
logits = logits[:, -1]
# handle contrastive decoding, Li et al.
# https://arxiv.org/abs/2210.15097
if exists(amateur_model):
for i, (amateur, amateur_cache, amateur_contrastive_decode_kwargs) in enumerate(zip(amateur_model, amateur_caches, contrastive_decode_kwargs)):
amateur_logits, next_amateur_cache = amateur(
x,
return_intermediates = True,
cache = amateur_cache,
seq_start_pos = seq_start_pos,
**kwargs
)
amateur_logits = amateur_logits[:, -1]
assert amateur_logits.shape == logits.shape, 'logits dimension are not the same between amateur and expert model'
logits = contrastive_decode_fn(logits, amateur_logits, **amateur_contrastive_decode_kwargs)
if cache_kv and amateur.can_cache_kv:
amateur_caches[i] = next_amateur_cache
# filter by top_k, top_p (nucleus), top_a, or custom
if greedy:
sample = logits.argmax(dim = -1, keepdim = True)
else:
filtered_logits = filter_logits_fn(logits, **filter_kwargs)
probs = F.softmax(filtered_logits / temperature, dim=-1)
sample = torch.multinomial(probs, 1)
# concat sample
out = torch.cat((out, sample), dim=-1)
if verbose:
if sl % 32 == 0:
print(sl, '/', seq_len)
if not exists(eos_token):
continue
is_eos_tokens = (out == eos_token)
if is_eos_tokens.any(dim = -1).all():
if verbose:
print('Model called the end of sequence at:', sl, '/', seq_len)
break
if exists(eos_token):
# mask out everything after the eos tokens
shifted_is_eos_tokens = F.pad(is_eos_tokens, (1, -1))
mask = shifted_is_eos_tokens.float().cumsum(dim = -1) >= 1
out = out.masked_fill(mask, self.pad_value)
if return_prime:
out = out[:, :]
else:
out = out[:, t:]
out, = unpack(out, ps, '* n')
return out
def compute_accuracy(self, logits, labels):
out = torch.argmax(logits, dim=-1)
out = out.flatten()
labels = labels.flatten()
mask = (labels != self.ignore_index) # can also be self.pad_value (your choice)
out = out[mask]
labels = labels[mask]
num_right = (out == labels)
num_right = torch.sum(num_right).type(torch.float32)
acc = num_right / len(labels)
return acc
def forward(self, x, return_outputs = False, **kwargs):
seq, ignore_index, add_attn_z_loss = x.shape[1], self.ignore_index, self.add_attn_z_loss
inp, target = x[:, :-1], x[:, 1:]
inp = torch.where(inp == ignore_index, self.pad_value, inp)
if self.mask_prob > 0.:
rand = torch.randn(inp.shape, device = x.device)
rand[:, 0] = -torch.finfo(rand.dtype).max # first token should not be masked out
num_mask = min(int(seq * self.mask_prob), seq - 1)
indices = rand.topk(num_mask, dim = -1).indices
mask = ~torch.zeros_like(inp).scatter(1, indices, 1.).bool()
kwargs.update(self_attn_kv_mask = mask)
logits, cache = self.net(
inp,
return_intermediates = True,
return_attn_z_loss = add_attn_z_loss,
**kwargs
)
acc = self.compute_accuracy(logits, target)
loss_fn = F.cross_entropy if not self.net.output_is_log_prob else F.nll_loss
loss = loss_fn(
rearrange(logits, 'b n c -> b c n'),
target,
ignore_index = ignore_index
)
if add_attn_z_loss:
loss = loss + cache.attn_z_loss
if not return_outputs:
return loss, acc
return loss, acc, logits, cache
#=================================================================================================================================
# This is the end of x_transformer_2_3_1 Python module
#================================================================================================================================= |