[petsc-users] Exploiting symmetry with direct solvers

[Hong]

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;
...

Hong
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