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import torch | ||
from typing import Tuple, Callable | ||
import math | ||
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def do_nothing(x: torch.Tensor, mode:str=None): | ||
return x | ||
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def bipartite_soft_matching_random2d(metric: torch.Tensor, | ||
w: int, h: int, sx: int, sy: int, r: int, | ||
no_rand: bool = False) -> Tuple[Callable, Callable]: | ||
""" | ||
Partitions the tokens into src and dst and merges r tokens from src to dst. | ||
Dst tokens are partitioned by choosing one randomy in each (sx, sy) region. | ||
Args: | ||
- metric [B, N, C]: metric to use for similarity | ||
- w: image width in tokens | ||
- h: image height in tokens | ||
- sx: stride in the x dimension for dst, must divide w | ||
- sy: stride in the y dimension for dst, must divide h | ||
- r: number of tokens to remove (by merging) | ||
- no_rand: if true, disable randomness (use top left corner only) | ||
""" | ||
B, N, _ = metric.shape | ||
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if r <= 0: | ||
return do_nothing, do_nothing | ||
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with torch.no_grad(): | ||
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hsy, wsx = h // sy, w // sx | ||
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# For each sy by sx kernel, randomly assign one token to be dst and the rest src | ||
idx_buffer = torch.zeros(1, hsy, wsx, sy*sx, 1, device=metric.device) | ||
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if no_rand: | ||
rand_idx = torch.zeros(1, hsy, wsx, 1, 1, device=metric.device, dtype=torch.int64) | ||
else: | ||
rand_idx = torch.randint(sy*sx, size=(1, hsy, wsx, 1, 1), device=metric.device) | ||
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idx_buffer.scatter_(dim=3, index=rand_idx, src=-torch.ones_like(rand_idx, dtype=idx_buffer.dtype)) | ||
idx_buffer = idx_buffer.view(1, hsy, wsx, sy, sx, 1).transpose(2, 3).reshape(1, N, 1) | ||
rand_idx = idx_buffer.argsort(dim=1) | ||
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num_dst = int((1 / (sx*sy)) * N) | ||
a_idx = rand_idx[:, num_dst:, :] # src | ||
b_idx = rand_idx[:, :num_dst, :] # dst | ||
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def split(x): | ||
C = x.shape[-1] | ||
src = x.gather(dim=1, index=a_idx.expand(B, N - num_dst, C)) | ||
dst = x.gather(dim=1, index=b_idx.expand(B, num_dst, C)) | ||
return src, dst | ||
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metric = metric / metric.norm(dim=-1, keepdim=True) | ||
a, b = split(metric) | ||
scores = a @ b.transpose(-1, -2) | ||
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# Can't reduce more than the # tokens in src | ||
r = min(a.shape[1], r) | ||
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node_max, node_idx = scores.max(dim=-1) | ||
edge_idx = node_max.argsort(dim=-1, descending=True)[..., None] | ||
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unm_idx = edge_idx[..., r:, :] # Unmerged Tokens | ||
src_idx = edge_idx[..., :r, :] # Merged Tokens | ||
dst_idx = node_idx[..., None].gather(dim=-2, index=src_idx) | ||
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def merge(x: torch.Tensor, mode="mean") -> torch.Tensor: | ||
src, dst = split(x) | ||
n, t1, c = src.shape | ||
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unm = src.gather(dim=-2, index=unm_idx.expand(n, t1 - r, c)) | ||
src = src.gather(dim=-2, index=src_idx.expand(n, r, c)) | ||
dst = dst.scatter_reduce(-2, dst_idx.expand(n, r, c), src, reduce=mode) | ||
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return torch.cat([unm, dst], dim=1) | ||
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def unmerge(x: torch.Tensor) -> torch.Tensor: | ||
unm_len = unm_idx.shape[1] | ||
unm, dst = x[..., :unm_len, :], x[..., unm_len:, :] | ||
_, _, c = unm.shape | ||
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src = dst.gather(dim=-2, index=dst_idx.expand(B, r, c)) | ||
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# Combine back to the original shape | ||
out = torch.zeros(B, N, c, device=x.device, dtype=x.dtype) | ||
out.scatter_(dim=-2, index=b_idx.expand(B, num_dst, c), src=dst) | ||
out.scatter_(dim=-2, index=a_idx.expand(B, a_idx.shape[1], 1).gather(dim=1, index=unm_idx).expand(B, unm_len, c), src=unm) | ||
out.scatter_(dim=-2, index=a_idx.expand(B, a_idx.shape[1], 1).gather(dim=1, index=src_idx).expand(B, r, c), src=src) | ||
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return out | ||
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return merge, unmerge | ||
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def get_functions(x, ratio, original_shape): | ||
b, c, original_h, original_w = original_shape | ||
original_tokens = original_h * original_w | ||
downsample = int(math.sqrt(original_tokens // x.shape[1])) | ||
stride_x = 2 | ||
stride_y = 2 | ||
max_downsample = 1 | ||
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if downsample <= max_downsample: | ||
w = original_w // downsample | ||
h = original_h // downsample | ||
r = int(x.shape[1] * ratio) | ||
no_rand = False | ||
m, u = bipartite_soft_matching_random2d(x, w, h, stride_x, stride_y, r, no_rand) | ||
return m, u | ||
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nothing = lambda y: y | ||
return nothing, nothing |
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