I want to vary the number of threads active in fft/fftn. I test on R2011b:
A = randn([2048 2048]); maxNumCompThreads(N) for a=1:100 A = fftn(A); end
with different N. However, when varying N, nothing change in the core CPU monitoring: all the cores stay active.
It seems that the fftw library does not take into account the number of cores. Is there a way to specify this parameter in fftw ? Is there another way to define the number of active cores ?
Don't know if this is any help, but:
maxNumCompThreads will be removed in a future release. Please remove any instances of this function from your code.
Function was removed in 2012a:
It's possible that it was being systematically removed from functions such as fftn() prior to that release (?)
I just tried it out on my Windows install (R2011b). No matter what you set maxNumCompThreads to, fftn only ever uses one thread. It's simply not multithreaded.
edit: Something funky was happening with my system when I tested this -- it is multithreaded.