Stopping criteria

[Nguyen, Hung V ERDC-ITL-MS]

Hello,

> CG does not work for indefinite matrices, the natural thing to try is
-ksp_type minres.  You can also try a nonsymmetric KSP which gives you more
choices for preconditioning, although good preconditioning for an indefinite
matrix generally uses problem-specific information.  Where does this matrix
come from?  How scalable does the solver need to be?

This matrix is from CFD application and supposed to be SPD. The CFD used cg
solver with jacobi preconditioner. It took a large number of iterations for
the true residual norm drops by about 6 orders of magnitude.

Thank you for the info. 

-hung 
    

 

-----Original Message-----
From: owner-petsc-users at mcs.anl.gov [mailto:owner-petsc-users at mcs.anl.gov] On
Behalf Of Jed Brown
Sent: Wednesday, January 14, 2009 3:15 PM
To: petsc-users at mcs.anl.gov
Subject: Re: Stopping criteria

On Wed, Jan 14, 2009 at 10:54, Nguyen, Hung V ERDC-ITL-MS
<Hung.V.Nguyen at usace.army.mil> wrote:
> Linear solve did not converge due to DIVERGED_INDEFINITE_MAT 
> iterations 9

CG does not work for indefinite matrices, the natural thing to try is
-ksp_type minres.  You can also try a nonsymmetric KSP which gives you more
choices for preconditioning, although good preconditioning for an indefinite
matrix generally uses problem-specific information.  Where does this matrix
come from?  How scalable does the solver need to be?

Jed