[petsc-dev] DMGetMatrix --> DMGetMatrices?

[Dmitry Karpeev]

On Fri, Feb 10, 2012 at 7:57 PM, Jed Brown <jedbrown at mcs.anl.gov> wrote:

> On Fri, Feb 10, 2012 at 19:51, Dmitry Karpeev <karpeev at mcs.anl.gov> wrote:
>
>> How does this explanation square with the following code from KSPSetUp?
>>
>>  if (ksp->dmActive && !ksp->setupstage) {
>>     /* first time in so build matrix and vector data structures using DM
>> */
>>     if (!ksp->vec_rhs) {ierr =
>> DMCreateGlobalVector(ksp->dm,&ksp->vec_rhs);CHKERRQ(ierr);}
>>     if (!ksp->vec_sol) {ierr =
>> DMCreateGlobalVector(ksp->dm,&ksp->vec_sol);CHKERRQ(ierr);}
>>     ierr = DMCreateMatrix(ksp->dm,MATAIJ,&A);CHKERRQ(ierr);
>>     ierr = KSPSetOperators(ksp,A,A,stflg);CHKERRQ(ierr);
>>     ierr = PetscObjectDereference((PetscObject)A);CHKERRQ(ierr);
>>  }
>>
>
> Look down the page a little, DMComputeJacobian() is what actually
> assembles.
>
>     if (ksp->setupstage != KSP_SETUP_NEWRHS) {
>       ierr = KSPGetOperators(ksp,&A,&A,PETSC_NULL);CHKERRQ(ierr);
>       ierr =
> DMComputeJacobian(ksp->dm,PETSC_NULL,A,A,&stflg);CHKERRQ(ierr);
>       ierr = KSPSetOperators(ksp,A,A,stflg);CHKERRQ(ierr);
>     }
>
> Okay.  Then what's the need for DMSetPreallocateOnly()?

Dmitry.
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