UseParallel + mexcuda: how to obtain CPU thread number?

I am using fsolve to solve a root-finding problem. The function evaluation component is expensive so I have written a mexcuda program to make use of GPUs. I have multiple GPUs on my system.

I would like to enable the "UseParallel" feature to compute Jacobians in parallel, with each instance of the evaluation calling a separate GPU. So my final program will look something like this:

root = fsolve(@objfun, "UseParallel", true);

function z = objfun(x)
    z = GPUfunction(x, GPUdeviceToUse)
end

I would like to set the GPUdeviceToUse variable to depend on the CPU thread ID used within the "UseParallel" feature.

How can I obtain the CPU thread ID?

Answer 1

[Walter Roberson]

See https://www.mathworks.com/matlabcentral/answers/568620-is-it-possible-to-identify-workers-when-using-parallel-computing-in-optimization-routines#comment_1025185

I would expect that fsolve() has the same kind of initialization to verify that the function basically works, so there might be one invocation for which there is no thread . Maybe even one round to estimate the jacobian.