[petsc-users] DMPlex and Tao

[Justin Chang]

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.


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
>
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