[petsc-users] QCG and KSPSetPCSide

[Matthew Knepley]

On Mon, Jun 29, 2015 at 9:22 AM, <Carol.Brickley at awe.co.uk> wrote:

> All,
>
> I am trying to use KSPSolve for a QCG solver using petsc 3.4.3 and it
> gives me the error of "PC does not have left symmetric apply!". Further
> reading on the web pages suggest I


CG is the Krylov Solver (KSP), but the error message is about the
Preconditioner (PC). QCG by default uses symmetric application, and by
default the PC is ILU which does not have a symmetric apply. You can use
-ksp_pc_side left

  Thanks,

     Matt


> need to use KSPSetPCSide to set up a symmetric side for the solver.
> However, this does not seem to work. I am doing the following in an F90
> code:
>
> call KSPSetPCType(ksp_ptr%ksp, 'qcg', petsc_err)
> call KSPSetPCSide(ksp_ptr%ksp, PC_SYMMETRIC, petsc_err)
>
> but I still get the same failure message when I call
> KSPSolve(ksp_ptr%ksp..)  later on.
>
> Any ideas as to why this is not working?
>
> Carol
>
>
>
>
>
> Dr Carol Brickley
> BSc,PhD,ARCS,DIC,MBCS
>
> Senior Software Engineer
> Applied Computer Science
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> AWE
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>
> Direct: 0118 9855035
>
>
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