[petsc-users] unable to set type "agg" in GAMG preconditioner

[Mark F. Adams]

On Nov 7, 2012, at 8:58 AM, A.L. Siahaan <als88 at cam.ac.uk> wrote:

> Hi, I am experimenting with GAMG by changing some of its parameters. I tried to set the GAMG type into "agg" using : PCGAMGSetType(pc,"agg");
> 
> and I get the following error : 
> ========================================================================== Solving linear system of size 108972 x 108972 (PETSc Krylov solver). demo_elasticity: /usr/local/packages/src/petsc-3.3/src/ksp/pc/impls/gamg/agg.c:1522: PCCreateGAMG_AGG: Assertion `!pc_gamg->subctx' failed. ==========================================================================
> 

I've pushed a fix into petsc-dev.

> Is there any other parameter which needs to be set to enable "agg" ?

This is usually set from the command line but you are doing it correctly as far as I can tell.

> And what is the default type if I don't set to either "agg" or "geo" ?

'agg' is the default.

Thanks,
Mark

> 
> Thanks,
> Antony
>