cls_attn = attn[:, :, 0, 1:]

[Bugs-Bunny01]

hi，thank you for your contributions to open source.
but i have a problem.
cls_attn = attn[:, :, 0, 1:]
What does this code mean？

[Bugs-Bunny01]

What do the four dimensions represent?

[youweiliang]

Hi,
Thanks for your interest.
The attn has 4 dimensions representing [batch size, number of heads, number of tokens, number of tokens]. The last two dimensions represent the attention maps on the images.
The line cls_attn = attn[:, :, 0, 1:] is to extract the class attention (the attention values of the class token to the image tokens). As the class token is the first token, that leads to the slice [0, 1:] in the attention maps.

[Bugs-Bunny01]

感谢您的回复，也就是说，attn的第三个维度的0代表着cls-token，第四个维度1：代表着除了cls，其他的token吗

[youweiliang]

Yes!