[petsc-users] PC Shell Left, Right, Symm?

[Robert Ellis]

Hello Experts,

When using a KSP Shell PreConditioner, is the LEFT, RIGHT, SYMMETRIC option applicable?

      call KSPGetPC(ksp,pc,ierr)
      call PCSetType(pc,PCSHELL,ierr)
      call KSPSetPreconditionerSide(ksp,PC_SYMMETRIC,ierr)
      call PCShellSetApply(pc,JacobiShellPCApply,ierr)

The JacobiShellPCApply PreConditioner improves convergence considerably on my KSPCG problem. However, I have found empirically that using PC_LEFT, PC_RIGHT, PC_SYMMETRIC seems to have no effect on the convergence of the solution. Can anyone explain this unusual situation?

Thanks in advance for any help.
Cheers,
Rob
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