ScaledPlan: region subfield missing (needed for AD)

[maximilian-gelbrecht]

The ScaledPlan like e.g. the result of plan_fft has no field region, leading to an error when attempting to AD it via Zygote. Zygote (which depends on AbstractFFT) is requiring a region subfield.

Example

begin
    using Flux
    using Zygote
    using LinearAlgebra
    using FFTW
end

N = 15
data = rand(Float64, N)

FT = plan_fft(data) # e.g. plan_dct / plan_idct would work 
iFT= plan_ifft(data)

m = Chain(x->FT*x, Dense(N,N), x->iFT*x)
loss(x,y) = sum(abs2,m(x) .- y)
loss(data,data) # precompile

grads = gradient(() -> loss(data, data), params(m))

[stevengj]

Seems like this could be added (to AbstractFFTs.jl, not here).

[devmotion]

This was fixed in JuliaMath/AbstractFFTs.jl#65 which is about to be released in AbstractFFTs 1.2.0 (JuliaRegistries/General#63431). There is a function fftdims now that can be used to access the transformed region. It defaults to plan.region for plans that are subtypes of Plan, and does the right thing for ScaledPlans.