121 lines
3.5 KiB
Python
121 lines
3.5 KiB
Python
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# modified from https://github.com/mlfoundations/open_flamingo/blob/main/open_flamingo/src/helpers.py
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import math
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import torch
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import torch.nn as nn
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# FFN
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def FeedForward(dim, mult=4):
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inner_dim = int(dim * mult)
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return nn.Sequential(
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nn.LayerNorm(dim),
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nn.Linear(dim, inner_dim, bias=False),
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nn.GELU(),
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nn.Linear(inner_dim, dim, bias=False),
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)
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def reshape_tensor(x, heads):
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bs, length, width = x.shape
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#(bs, length, width) --> (bs, length, n_heads, dim_per_head)
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x = x.view(bs, length, heads, -1)
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# (bs, length, n_heads, dim_per_head) --> (bs, n_heads, length, dim_per_head)
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x = x.transpose(1, 2)
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# (bs, n_heads, length, dim_per_head) --> (bs*n_heads, length, dim_per_head)
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x = x.reshape(bs, heads, length, -1)
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return x
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class PerceiverAttention(nn.Module):
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def __init__(self, *, dim, dim_head=64, heads=8):
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super().__init__()
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self.scale = dim_head**-0.5
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self.dim_head = dim_head
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self.heads = heads
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inner_dim = dim_head * heads
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self.norm1 = nn.LayerNorm(dim)
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self.norm2 = nn.LayerNorm(dim)
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self.to_q = nn.Linear(dim, inner_dim, bias=False)
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self.to_kv = nn.Linear(dim, inner_dim * 2, bias=False)
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self.to_out = nn.Linear(inner_dim, dim, bias=False)
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def forward(self, x, latents):
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"""
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Args:
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x (torch.Tensor): image features
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shape (b, n1, D)
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latent (torch.Tensor): latent features
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shape (b, n2, D)
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"""
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x = self.norm1(x)
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latents = self.norm2(latents)
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b, l, _ = latents.shape
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q = self.to_q(latents)
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kv_input = torch.cat((x, latents), dim=-2)
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k, v = self.to_kv(kv_input).chunk(2, dim=-1)
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q = reshape_tensor(q, self.heads)
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k = reshape_tensor(k, self.heads)
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v = reshape_tensor(v, self.heads)
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# attention
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scale = 1 / math.sqrt(math.sqrt(self.dim_head))
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weight = (q * scale) @ (k * scale).transpose(-2, -1) # More stable with f16 than dividing afterwards
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weight = torch.softmax(weight.float(), dim=-1).type(weight.dtype)
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out = weight @ v
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out = out.permute(0, 2, 1, 3).reshape(b, l, -1)
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return self.to_out(out)
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class Resampler(nn.Module):
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def __init__(
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self,
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dim=1024,
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depth=8,
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dim_head=64,
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heads=16,
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num_queries=8,
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embedding_dim=768,
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output_dim=1024,
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ff_mult=4,
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):
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super().__init__()
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self.latents = nn.Parameter(torch.randn(1, num_queries, dim) / dim**0.5)
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self.proj_in = nn.Linear(embedding_dim, dim)
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self.proj_out = nn.Linear(dim, output_dim)
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self.norm_out = nn.LayerNorm(output_dim)
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self.layers = nn.ModuleList([])
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for _ in range(depth):
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self.layers.append(
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nn.ModuleList(
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[
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PerceiverAttention(dim=dim, dim_head=dim_head, heads=heads),
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FeedForward(dim=dim, mult=ff_mult),
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]
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)
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)
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def forward(self, x):
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latents = self.latents.repeat(x.size(0), 1, 1)
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x = self.proj_in(x)
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for attn, ff in self.layers:
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latents = attn(x, latents) + latents
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latents = ff(latents) + latents
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latents = self.proj_out(latents)
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return self.norm_out(latents)
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