How can I make expm running on many cores?

I need to compute the exponential of large matrices. I am using the instruction expm and I would like to make it running on a parallel manner.

How can I make this function running on many cores? For instance the example below is still running on one core.

delete (gcp('nocreate'))

parpool(4);

ntot=2^12

Atot=rand(ntot,ntot);

expm(Atot);

Answer 1

[Raymond Norris]

Starting a parallel pool doesn't run subsequent MATLAB code in parallel, it simple starts a colletion of headless MATLAB processes. You need to use a parallel construct (e.g., parfor, gpuArray, etc.) to explicitly parallelize the code.

Regarding your code, expm is already using multi-core. You can test this via the following example. For this I'm running MATLAB R2022a on a 12-core VM.

maxNumCompThreads(1);
ntot=2^12;
Atot=rand(ntot,ntot);
tic, expm(Atot); toc
Elapsed time is 27.851388 seconds.

maxNumCompThreads(4);
ntot=2^12;
Atot=rand(ntot,ntot);
tic, expm(Atot); toc
Elapsed time is 7.882113 seconds.

maxNumCompThreads(12);
ntot=2^12;
Atot=rand(ntot,ntot);
tic, expm(Atot); toc
Elapsed time is 3.815132 seconds.

MATLAB is already implicitly parallelizing expm.