# with a caching mechanism for keys and values to avoid a O(N^3) cost
# for auto-regression.
+# This implementation is equipped with RNN layers to replace the MHA
+
import math, warnings
import torch, einops
# 1 for the successive tokens.
#
# Modules able to process brackets may implement a cache that is
-# resetted when the input bracket starts at t=0
+# resetted when init_cache is True
class BracketedSequence:
##############################
+# Returns a tensor with an additional index at rank win_dim, that move
+# along the same dimension as dim, on a domain {0...win_size-1}, and
+# dim is restricted on a domain reduced by win_size-1 values.
+
+
def moving_window(x, dim, win_dim, win_size):
size, stride = x.size(), x.stride()
size = size[:dim] + (size[dim] - win_size + 1,) + size[dim + 1 :]
warnings.warn("Caterpillar", RuntimeWarning)
- def randw(*d):
- return nn.Parameter(torch.randn(*d) / math.sqrt(d[-1]))
+ def randw(*d, amplitude=None):
+ if amplitude is None:
+ amplitude = 1 / math.sqrt(d[-1])
+ return nn.Parameter(amplitude * torch.randn(*d))
self.caterpillar_length = caterpillar_length
self.caterpillar_height = caterpillar_height
self.attention_dropout = attention_dropout
- self.w_G = randw(nb_heads, caterpillar_height, dim_model)
+ self.proba_gate_dropout = 0.0
+
+ self.w_G = randw(nb_heads, caterpillar_height, dim_model, amplitude=1e-5)
self.b_G = nn.Parameter(
torch.full(
(nb_heads, caterpillar_height), -math.log(caterpillar_height - 1)
self.w_Q = randw(nb_heads, dim_qk, dim_model)
self.w_O = randw(dim_v * nb_heads, dim_model)
- self.init_K_rec = randw(caterpillar_height, caterpillar_length, dim_qk)
- self.init_V_rec = randw(caterpillar_height, caterpillar_length, dim_v)
+ self.init_K_rec = randw(
+ caterpillar_height, caterpillar_length, dim_qk, amplitude=1e-5
+ )
+ self.init_V_rec = randw(
+ caterpillar_height, caterpillar_length, dim_v, amplitude=1e-5
+ )
def reset_inner_loss(self):
self.acc_attention = 0
N = bs.x.size(0)
T = bs.x.size(1)
+ H = self.w_V.size(0)
DV = self.w_V.size(1)
DK = self.w_K.size(1)
- Dout = self.w_O.size(1)
+ DM = self.w_O.size(1)
CH = self.caterpillar_height
CL = self.caterpillar_length
t0 >= CL and (t1 - t0) % CL == 0
), f"bs.first should be greater than caterpillar_length, and bs.nb should be a multiple of caterpillar_length"
+ # We cache values to deal efficiently with auto-regression
+
if bs.init_cache:
self.rec_V = X.new_zeros(N, CH, T, DV)
self.rec_K = X.new_zeros(N, CH, T, DK)
self.rec_V[:, :, t0 - CL : t0] = self.init_V_rec[None, :, :, :]
self.rec_K[:, :, t0 - CL : t0] = self.init_K_rec[None, :, :, :]
- self.cache_Y = X.new_zeros(N, T, Dout)
+ self.cache_Y = X.new_zeros(N, T, DM)
+
+ V = torch.einsum("ntc,hdc->nhtd", X, self.w_V)
+ K = torch.einsum("ntc,hdc->nhtd", X, self.w_K)
######################################################################
# Compute the recurrent state
- # This is the Gating sequence that modulates if they key and
- # values should be stored in one of the CH pairs of the
- # current stack. The CH gating values are independent, which
- # means that the same thing could be stored up to CH times or
- # not at all
+ # This is the Gating sequence that modulates the storing of
+ # the new key and value in the CH pairs of the current
+ # stack. There are CH independent gating values, which means
+ # that the current K/V may be stored in multiple pairs of the
+ # recurrent state, or not at all.
G = (
- torch.einsum("ntc,hec->nhet", X, self.w_G) + self.b_G[None, :, :, None]
+ torch.einsum("ntc,hrc->nhrt", X, self.w_G) + self.b_G[None, :, :, None]
).sigmoid()
- V = torch.einsum("ntc,hdc->nhtd", X, self.w_V)
- K = torch.einsum("ntc,hdc->nhtd", X, self.w_K)
+ ######################################################################
+ # The "flashbacks"
+
+ if self.training and self.proba_gate_dropout > 0.0:
+ # This is a better implementation of "flashbacks".
+
+ # G is NxHxExT where e is the caterpillar's row.
+
+ warnings.warn("gate dropout", RuntimeWarning)
+ epsilon = 0.5
+
+ dropout_start = (
+ (
+ torch.rand(G.size(), device=G.device)
+ .flatten(2, 3)
+ .sort(dim=2)
+ .indices
+ == 0
+ )
+ .unflatten(2, (CH, t1 - t0))
+ .float()
+ )
+
+ dropout_tail = dropout_start.cumsum(dim=3) - dropout_start
+
+ dropout_active = (
+ torch.rand(N, 1, 1, 1, device=G.device) < self.proba_gate_dropout
+ ).long()
+
+ dropout_start *= dropout_active
+ dropout_tail *= dropout_active
+
+ G = (
+ G
+ + dropout_start * (1 - epsilon - G.detach())
+ - dropout_tail * G.detach()
+ )
+
+ ######################################################################
# We prepare the arguments for the parallel scan
+ # Clip the gating to avoid values greater than 1 when several
+ # heads hit the same row
+
+ G = G / G.sum(1, keepdim=True).clamp(min=1)
+
A = 1 - G.sum(1)
- gated_V = torch.einsum("nhet,nhtd->netd", G, V)
- gated_K = torch.einsum("nhet,nhtd->netd", G, K)
+ gated_V = torch.einsum("nhrt,nhtd->nrtd", G, V)
+ gated_K = torch.einsum("nhrt,nhtd->nrtd", G, K)
+
+ # We start from cached values, which matters in inference
init_rec_V = self.rec_V[:, :, t0 - CL : t0]
init_rec_K = self.rec_K[:, :, t0 - CL : t0]
- # Here there is a trick: The parallel scan operates with a
- # period of L, so we split the sequence indexing in two axes,
- # the second of size CL, and run the parallel scan using the
- # other alone as the sequence index.
+ #################################################################
+ # Associative scan
+
+ # Here there is a trick: Since the stack at position t is
+ # computed by updating that at position t-CL, the parallel
+ # scan operates with a period of CL. To do so we split the
+ # sequence indexing in two axes, the second of size CL, and
+ # run the parallel scan using the first as the sequence index.
A = A.unflatten(2, (-1, CL))
gated_V = gated_V.unflatten(2, (-1, CL))
next_V = pscan_dim(A, gated_V, init_rec_V, dim=2)
next_K = pscan_dim(A, gated_K, init_rec_K, dim=2)
- # Put back the sequence index
-
self.rec_V[:, :, t0:t1] = next_V.flatten(2, 3)
self.rec_K[:, :, t0:t1] = next_K.flatten(2, 3)
nb_blocks,
nb_lines=None,
caterpillar_height=None,
- dim_rec_v=-1,
causal=False,
dropout=0.0,
len_max=1e5,
):
super().__init__()
- assert attention_layer in {"mha", "dumbrec", "kvrec", "caterpillar"}
+ assert attention_layer in {
+ "mha",
+ "dumbrec",
+ "kvrec",
+ "caterpillar",
+ }, f"Unknown attention operator {attention_layer}."
if attention_layer == "caterpillar":
assert nb_lines % caterpillar_height == 0
return DumbRec(
dim_model=dim_model,
dim_qk=dim_keys,
- dim_v=dim_rec_v,
+ dim_v=dim_model // nb_heads,
nb_heads=nb_heads,
nb_lines=nb_lines,
attention_dropout=dropout,
return KVRec(
dim_model=dim_model,
dim_qk=dim_keys,
- dim_v=dim_rec_v,
+ dim_v=dim_model // nb_heads,
nb_heads=nb_heads,
nb_lines=nb_lines,
attention_dropout=dropout,
return Caterpillar(
dim_model=dim_model,
dim_qk=dim_keys,
- dim_v=dim_rec_v,
+ dim_v=dim_model // nb_heads,
nb_heads=nb_heads,
caterpillar_length=self.caterpillar_length,
caterpillar_height=self.caterpillar_height,
projects / mygptrnn.git / blobdiff