Kron error when dealing with sparse gpuarrays

When I attempt to use kron with a sparse gpu array as an input on R2019a, I get the following error:

"Error using matlab.internal.sparse.kronSparse

Input must be a sparse matrix."

This indicates to me that MATLAB is having issues either making or recognizing when gpuarrays are made sparse, since I've done the simple test case:

a = gpuarray([1 2]);
b = gpuarray([1 2]);
test1 = kron(a,b)

a = sparse(a)
test2 = kron(a,b)

and only the assignment of test2 gives the error. Does anyone know if there's a workaround for this, or am I stuck with using my cpu for these calculations?

[Walter Roberson]

b is not sparse in your test2 call.

[Matt J]

Also, what operations will be done subsequently with kron(a,b) once it is computed? Knowing that, one can often find workarounds that avoid computing the Kronecker product altogether.

[Henry Abrahamson]

I know that b isn't sparse, there's a line in the kron function (like 37 or something) that's supposed to make b sparse and then pass it to that internal function, but the fact that it doesn't work for me is my whole issue.

The Kronecker is just being used to simplify a bit of matrix multiplication I'd have to do. But now that you mention it, I think I see a way to do it the long way (in terms of some extra lines of code) that should get the same results without a terrible performance hit. Thanks for the tip!

Answer 1

[Matt J]

You may want to look at,

https://www.mathworks.com/matlabcentral/fileexchange/25969-efficient-object-oriented-kronecker-product-manipulation

which allows you to do many kinds of manipulations with Kronecker products without computing them in explicit matrix form. It should work with gpuArray operands.