CG solver and preconditioner

[Matthew Knepley]

On 7/6/06, Matt Funk <mafunk at nmsu.edu> wrote:
>
> Hi,
>
> In the html web manual for PETSc:
>
> KSPCG is described as the preconditioned conjugate gradient iterative
> method
> with: The PCG method requires both the matrix and preconditioner to be
> symmetric positive (semi) definite.
>
> For KSPCG do you need to specify a preconditioner type ie: Jacobi or is
> there
> a default the KSPCG uses.


The default on 1 proc is ILU, and many is Block Jacobi.

Reason for question is that for the system I am solving I need to specify
> -pc_type none for KSPCG to run.  If I do not turn the PC off then the
> solver
> does not run.  Other KSP types like BiCG and GMRES work fine when I
> specify a
> PC.


I have no idea what "deos not run" means. CG should work with any
preconditioner
that applies an SPD matrix.

   Matt

-- 
"Failure has a thousand explanations. Success doesn't need one" -- Sir Alec
Guiness
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