why mkl can not get fft(x,1)?

[liushang0322]

please first create a random matrix x = rand(100,100,100) and then call the FFTW library. If you use FFTW.set_provider!("mkl") and then fft(x,1), it will report an error. What is the reason?

i always get ERROR: FFTW could not create plan

[tkuraku]

It looks like it cannot do fft along a given axis for arrays with more than two dimensions. Seems like either a major regression or some missing functionality.

import FFTW

# %% Works perfectly
a = ones(Float64, 64, 64);
iffta = FFTW.fft(a, 1)

# %% ERROR: FFTW could not create plan 
b = ones(Float64, 64, 64, 64);
iffta = FFTW.fft(b, 1)

[stevengj]

This is a documented and longstanding limitation of MKL, which does not support the full functionality of FFTW. See the fourth bullet point in Intel's list of unsupported features:

That is, it can't handle multiple nested loops of FFTs, only a single loop of FFTs. A workaround for the first or last dimensions would be to reshape the array to group the other dimensions together, in which case it can handle it, but it still won't be able to transform the middle dimension.

Or you could just use FFTW.