[petsc-dev] DMGetMatrix --> DMGetMatrices?

[Dmitry Karpeev]

On Fri, Feb 10, 2012 at 8:11 PM, Dmitry Karpeev <karpeev at mcs.anl.gov> wrote:

>
>
> 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()?
>
Oh, I see: preallocate the space, but don't set the exact sparsity pattern.
Dmitry.

>
> Dmitry.
>
>
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