FFTOptimize
FFTOptimize
Section Mesh::FFTs
Type logical
Default yes
Should octopus optimize the FFT dimensions?
This means that the mesh to which FFTs are applied is not taken to be as small
as possible: some points may be added to each direction in order to get a "good number"
for the performance of the FFT algorithm.
The best FFT grid dimensions are given by $2^a 3^b 5^c 7^d 11^e 13^f$
where $a,b,c,d$ are arbitrary and $e,f$ are 0 or 1.
(ref).
In some cases, namely when using
the split-operator, or Suzuki-Trotter propagators, this option should be turned off.
For spatial FFTs in periodic directions, the grid is never optimized, but a warning will
be written if the number is not good, with a suggestion of a better one to use, so you
can try a different spacing if you want to get a good number.