[petsc-users] Example for solving system of pde with snes

[Matthew Knepley]

On Sun, Sep 10, 2017 at 2:39 AM, Praveen C <cpraveen at gmail.com> wrote:

> Dear all
>
> I am solving 3 coupled first order PDE in 2-D with SNES. The stencil is
> (3+1+3) in both directions due to weno scheme. I want to use matrix-free
> gmres. For preconditioner, I will use first order scheme with stencil
> (1+1+1) in both directions. I am using DMDA.
>
> Two things that I am looking for are:
>
> How to setup the matrix ?
>
> Since I have 3 variables at each grid point, how to fill the jacobian
> matrix.
>
> Is there an existing example that comes close to this situation. My search
> was not fruitful.
>

No. You want 2 DAs, 1 for evaluating residuals with s = 3, and one for
making a Jacobian with s = 1. You give these
two DAs to

http://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/SNES/DMDASNESSetFunctionLocal.html
http://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/SNES/DMDASNESSetJacobianLocal.html

and I think it should work as you want. Its too bad we cannot handle this
case with SNESSetDM() since it only takes
a single DM and there is no way to specialize the Jacobian.

  Thanks,

    Matt

Thank you
> praveen
>



-- 
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

http://www.caam.rice.edu/~mk51/
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