[petsc-users] Exploiting symmetry with direct solvers

[David Knezevic]

On Wed, Apr 8, 2015 at 11:06 PM, Hong <hzhang at mcs.anl.gov> wrote:

> David:
>
>>
>>>> Mumps supports Cholesky factorization for symmetric, and symmetric+spd
>>> matrices.  You may consult mumps user manual.
>>>
>>
>>
>> OK, thanks. But I was also wondering about the PETSc interface to MUMPS.
>>
>> I consulted the MUMPS manual, but it just says that you need to specify
>> "SYM=1" in order to get an LDL^T factorization. I gather that if we set
>> MatSetOption(A,MAT_SPD,PETSC_TRUE); in PETSc then that will tell MUMPS to
>> use SYM=1, right?
>>
>
> When user requests Cholesky factorization, PETSc sets  "SYM=2" as default;
> If user sets flag of spd, then the interface uses "SYM=1" in order to get
> an LDL^T factorization. See MatGetFactor_xxx_mumps() in
> petsc/src/mat/impls/aij/mpi/mumps/mumps.c:
>
> ...
>  B->factortype = MAT_FACTOR_CHOLESKY;
>   if (A->spd_set && A->spd) mumps->sym = 1;
>   else                      mumps->sym = 2;
> ...
>


OK, got it, thanks!

David
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