[petsc-users] Using same DMPlex for solving two different problems

[Matthew Knepley]

On Fri, Apr 7, 2017 at 6:32 AM, Abhyankar, Shrirang G. <abhyshr at anl.gov>
wrote:

>
> On Apr 7, 2017, at 6:25 AM, Matthew Knepley <knepley at gmail.com> wrote:
>
> On Thu, Apr 6, 2017 at 1:04 PM, Abhyankar, Shrirang G. <abhyshr at anl.gov>
> wrote:
>
>> I am solving a time-dependent problem using DMNetwork (uses DMPlex
>> internally) to manage the network. To find the initial conditions, I need
>> to solve a nonlinear problem on the same network but with different number
>> of dofs on the nodes and edges.
>>
>> Question: Can I reuse the same DMNetwork (DMPlex) for solving the two
>> problems. The way I am trying to approach this currently is by creating
>> two PetscSections to be used with Plex. The first one is used for the
>> initial conditions and the second one is for the time-stepping. Here¹s the
>> code I have
>>
>
> This is the right way to do it, but its easier if you call DMClone() first
> to get a new
> DM with the same Plex, and then change its default Section and solve your
> problem
> with it.
>
>
> Thanks Matt. Doesn't DMClone() make a shallow copy for Plex? So any
> section set for the cloned Plex will also be set for the original one?
>

The Plex is just a reference, but its the implementation. The DM itself is
copied, so the Section is independent. That is the point.

  Thanks,

    Matt

>   Matt
>
>
>>
>>   for(i=vStart; i < vEnd; i++) {
>>     /* Two variables at each vertex for the initial condition problem */
>>     ierr = PetscSectionSetDof(dyn->initpflowpsection,i,2);CHKERRQ(ierr);
>>   }
>>   ierr = PetscSectionSetUp(dyn->initpflowpsection);CHKERRQ(ierr);
>>
>>   /* Get the plex dm */
>>   ierr = DMNetworkGetPlex(networkdm,&plexdm);CHKERRQ(ierr);
>>
>>   /* Get default sections associated with this plex set for time-stepping
>> */
>>   ierr = DMGetDefaultSection(plexdm,&dyn->defaultsection);CHKERRQ(ierr);
>> ierr =
>> DMGetDefaultGlobalSection(plexdm,&dyn->defaultglobalsection)
>> ;CHKERRQ(ierr);
>>
>> /* Increase the reference count so that the section does not get destroyed
>> when a new one is set with DMSetDefaultSection */
>> ierr =
>> PetscObjectReference((PetscObject)dyn->defaultsection);CHKERRQ(ierr);
>> ierr =
>> PetscObjectReference((PetscObject)dyn->defaultglobalsection)
>> ;CHKERRQ(ierr);
>>
>>
>>   /* Set the new section created for initial conditions */
>>   ierr = DMSetDefaultSection(plexdm,dyn->initpflowpsection);CHKERRQ(
>> ierr);
>>   ierr =
>> DMGetDefaultGlobalSection(plexdm,&dyn->initpflowpglobsection
>> );CHKERRQ(ierr)
>> ;
>>
>>
>>
>> Would this work or should I rather use DMPlexCreateSection to create the
>> PetscSection used for initial conditions (dyn->initpflowpsection)? Any
>> other problems that I should be aware of? Has anyone else attempted using
>> the same plex for solving two different problems?
>>
>> Thanks,
>> Shri
>>
>>
>>
>
>
> --
> What most experimenters take for granted before they begin their
> experiments is infinitely more interesting than any results to which their
> experiments lead.
> -- Norbert Wiener
>
>


-- 
What most experimenters take for granted before they begin their
experiments is infinitely more interesting than any results to which their
experiments lead.
-- Norbert Wiener
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