what should be the reference NFFT backend

[paquiteau]

Currently we are using pyNFFT as the reference backend to check the fidely of the other supported backend.
This result from a speed/precision compromise, because comparing all backends to the NDFT would be expensive

However this causes some troubles:

• as the method are not strictly NDFT, the triangle of comparison NDFT/NFFT/another_backend introduce more imprecision.
• PyNFFT does not seem to be actively maintained, and the installion is broken with new version of cython (see BUG: PyNFFT installation fails with Cython 3.0.0 pyNFFT/pyNFFT#75)

An alternative would be to use finufft as the reference implementation, as they have prime support for python bindings.

[ghisvail]

👋 PyNFFT author here

Indeed, I wrote the package a while back but the engagement around it has faded.

Feel free to submit a patch for Cython 3.0 if you succeed in making it work with it.

It's okay if you find an alternative implementation which performs better and is actively maintained.

Best regards from a fellow Inria engineer.