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Remove einsum in forward pass in AbstractAttention #783

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Remove einsum in forward pass in AbstractAttention #783

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18 changes: 10 additions & 8 deletions transformer_lens/components/abstract_attention.py
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Original file line number Diff line number Diff line change
Expand Up @@ -297,17 +297,19 @@ def forward(
)
)
else:
# Add singleton dimensions to make shapes compatible for broadcasting:
w = einops.rearrange(
self.W_O,
"head_index d_head d_model -> d_model head_index d_head",
"head_index d_head d_model -> 1 1 head_index d_head d_model",
)
result = self.hook_result(
einops.einsum(
z,
w,
"... head_index d_head, d_model head_index d_head -> ... head_index d_model",
)
) # [batch, pos, head_index, d_model]
z = einops.rearrange(
z, "batch pos head_index d_head -> batch pos head_index d_head 1"
)

# Multiply the z tensor by the W_O tensor, summing over the d_head dimension
unhooked_result = (z * w).sum(-2)

result = self.hook_result(unhooked_result) # [batch, pos, head_index, d_model]
out = (
einops.reduce(result, "batch position index model->batch position model", "sum")
+ self.b_O
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