On Mon, 29 May 2017 04:38:39 -0600, Jed Brown wrote:

Pierre Jolivet <[email protected]> writes:

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On 29 May 2017, at 06:49, Jed Brown <[email protected]> wrote:

You can't get a callback from this "external Krylov solver"?

You mean, a callback to let the external solver use the memory allocated by PETSc for the Mats? Unfortunately, I need the underlying memory to be contiguous between all Mats, and I don't think it is possible with the current PETSc operators for matrix creation.

You can allocate the full block, then pass portions of the (column-aligned) array in MatCreateDense().

So I was doing: MatCreate(); MatSetSizes(); MatSetType(); MatMPIDenseSetPreallocation(); MatAssemblyBegin(); MatAssemblyEnd(); MatMatMult(); and what you are suggesting is: MatCreateDense(); // data != nullptr as provided by the external solver so that there is no need for MatAssemblyBegin/MatAssemblyEnd http://www.mcs.anl.gov/petsc/petsc-current/src/mat/impls/dense/mpi/mpidense.... ? MatMatMult(); That makes perfect sense (assuming I'm not wrong about the MatAssemblyBegin/MatAssemblyEnd). MatSetUpMultiply_MPIDense would still be called at each iteration but I doubt this is too costly. Thanks for the help.