I have used something like this in similar situation

auto MatMult = [this](…args…)
{
   this->MyMatMult(…args…);
};


Then pass MatMult to petsc.

this refers to the class Global_Assem and we are assuming you are inside this class when doing the above.

best
praveen

On 30-Sep-2021, at 3:25 PM, Michael Wick <michael.wick.1980@gmail.com> wrote:

Hi:

I want to have the shell matrix-vector multiplication written as a class member function and pass it to the shell matrix via MatShellSetOperation. 

MatShellSetOperation(A, MATOP_MULT, (void (*)(void))(&Global_Assem::MyMatMult));

Perhaps I have a wrong understanding of function pointers, and I am constantly getting warnings that say I cannot convert a member function to a void type. The warning indeed makes sense to me, as the function pointer passed in the above manner is independent of an instance. Perhaps there are other ways of passing a member function that I don't know of. If you know how to address this, I would appreciate it a lot!

Thanks,

Mike