[petsc-users] Solving/creating SPD systems

[Matthew Knepley]

On Sat, Nov 28, 2015 at 12:10 AM, Justin Chang <jychang48 at gmail.com> wrote:

> Hi all,
>
> Say I have a saddle-point system for the mixed-poisson equation:
>
> [I  -grad] [u]  = [0]
> [-div  0  ] [p]     [-f]
>
> The above is symmetric but indefinite. I have heard that one could make
> the above symmetric and positive definite (SPD). How would I do that? And
> if that's the case, would this allow me to use CG instead of GMRES?
>

I believe you just multiply the bottom row by -1. You can use CG for an SPD
system, but you can
use MINRES for symmetric indefinite.

   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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