[petsc-dev] What should MatDuplicate_SeqAIJMKL() do?

[Barry Smith]

> On Jul 19, 2017, at 10:55 AM, Richard Tran Mills <rtmills at anl.gov> wrote:
> 
> Fellow PETSc developers,
> 
> I'm trying to figure out what my MatDuplicate() implementation for AIJMKL should do when the sparse inspector-executor model is being used. I think that the behavior should be
> 
> * If MAT_COPY_VALUES has been specified, then mkl_sparse_optimize() should be executed for the new matrix inside MatDuplicate_SeqAIJMKL().
> * If MAT_COPY_VALUES has not been specified, then don't do the mkl_sparse_optimize(), as the user is going to have to specify the nonzero entries at some point, and then do MatAssemblyBegin/End (which calls mkl_sparse_optimize).

   Richard,

    I don't think it matters. MatDuplicate() is always called after the matrix has been assembled so you do have the nonzero structure so presumably the mkl_sparse_optimize() can be called at the time of MatDuplicate(). Or you can wait until the next MatAssemblyEnd().

   Note that when this value is changed between MatAssemblys

 PetscObjectState       nonzerostate;     /* each time new nonzeros locations are introduced into the matrix this is updated */

 the nonzero structure has changed so you likely need to free the MKL optimize information and rebuild it with mkl_sparse_optimize.

  When state is changed the nonzero values have changed between MatAssembly 

  PetscObjectState     state;

 but not the nonzero structure. I don't know if the MKL optimized sparse matrices have optimizations for changing just the nonzeros vs changing the nonzero structure.

   Barry



> 
> I'm a little unclear on all of the situations in which MatDuplicate gets used, however, so let me know if I'm misunderstanding something.
> 
> Thanks,
> Richard