flip function assumes the input sequence is a Vector or List, it can be Matrix as well.

[sambitdash]

The flip

Flux.jl/src/layers/recurrent.jl

Line 57 in 88b0c65

flip(f, xs) = reverse(f.(reverse(xs)))

function assumes the input sequences are a list but mostly the data can be in matrix form. Multiplying with a cross-diagonal identity matrix can achieve this effectively. Moreover, Zygote does not support reverse of matrices.

[bhvieira]

Surely, but I don't see the point. Can you provide an example where flipping a matrix is necessary/useful?

[sambitdash]

In the recurrent network the xs can be a matrix and flip may be needed for all column elements.

[bhvieira]

In Flux it can't. Flux expects an array of arrays.

[sambitdash]

It's better to have matrices than vector of vectors.

[bhvieira]

I mean, that can make sense (specially if the 'timelike' dimension is the first index, due to memory addressing), but it's not the way Flux operates right now.

[sambitdash]

Anyway, writing a flip for matrices is just multiplying with cross-diagonal matrix so the workaround is not so hard. But, use of matrices makes the library much better usability is what I felt. Personally, I prefer using matrices for all recurrent operations.

[bhvieira]

@sambitdash which dimension of the matrix would you flip though? It makes sense only to flip the time-like dimension. Which one is it? What if you have a batch dimension?

[sambitdash]

My problem needed the time dimension flip. But guess dimension as a parameter can be useful.

[CarloLucibello]

flip doesn't exist anymore