[petsc-users] DMPlex and Tao

[Matthew Knepley]

On Wed, Jul 30, 2014 at 5:01 PM, Justin Chang <jychang48 at gmail.com> wrote:

> That's good to know thanks. I have another question somewhat related.
>
> In that quadratic programming problem I have shown earlier, my K matrix is
> of global size *Ndof* by *Ndof* where *Ndof* is number of free dofs (for
> instance, if I have a 2x2 quadrilateral mesh and want to evaluate
> concentration at all the verticies, I will have nine total dofs but if I
> have Dirichlet constraints all along the boundary, only my center vertex is
> free so *Ndof* = 1. Thus when I simply call DMCreateMatrix(...) it would
> give me a 1x1 matrix.)
>
> However, I want my M constraint matrix to be of size *Nele* by *Ndof*
> where *Nele* is the total number of elements. How would I create this
> matrix? Because ultimately, I am subjecting all of my free u's to *Nele*
> number of equality constraints, and if possible I want this M matrix to be
> compatible with the layout from Vec u.
>

This is not hard in principle. I used to have code that did this, but I
took it out during the rewrite because no one
was using it and it was complicated. It just generalizes the code in
DMPlexPreallocateOperator() to take two
PetscSections instead of one.

Are you sure that this does not belong inside a large square matrix for the
entire problem?

  Thanks,

     Matt


>
> On Wed, Jul 30, 2014 at 2:03 PM, Matthew Knepley <knepley at gmail.com>
> wrote:
>
>> On Wed, Jul 30, 2014 at 2:53 PM, Justin Chang <jychang48 at gmail.com>
>> wrote:
>>
>>> Hi,
>>>
>>> This might be a silly question, but I am developing a finite element
>>> code to solve the non-negative diffusion equation. I am using the DMPlex
>>> structure and plan on subjecting the problem to a bounded constraint
>>> optimization to ensure non-negative concentrations. Say for instance, I
>>> want to solve:
>>>
>>> min || K*u - F ||^2
>>> subject to u >= 0
>>>              M*u = 0
>>>
>>> Where K is the Jacobian, F the residual, u the concentration, and M some
>>> equality constraint matrix. I know how to do this via Tao, but my question
>>> is can Tao handle Mats and Vecs created via DMPlex? Because from the SNES
>>> and TS examples I have seen in ex12, ex62, and ex11, it seems there are
>>> solvers tailored to handle DMPlex created data structures.
>>>
>>
>> Yes, TAO can handle objects created by DMPlex since they are just Vec and
>> Mat structures. The additions
>> to ex12, ex62, and ex11 concern the callbacks from the solver to the
>> constructions routines for residual and
>> Jacobian. Right now, none of the callbacks are automatic for TAO so you
>> would have to code them yourself,
>> probably by just calling the routines from SNES or TS so it should not be
>> that hard. We are working to get
>> everything integrated as it is in the other solvers.
>>
>>   Thanks,
>>
>>      Matt
>>
>>
>>> Thanks,
>>> Justin
>>>
>>
>>
>>
>> --
>> 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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