[petsc-dev] Branches with additional features

[Pierre Jolivet]

On Mon, 29 May 2017 04:38:39 -0600, Jed Brown wrote:
> Pierre Jolivet <pierre.jolivet at enseeiht.fr> writes:
>
>>> On 29 May 2017, at 06:49, Jed Brown <jed at jedbrown.org> 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.c.html#line1473 
?
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.