[petsc-users] Matrix-free preconditioner using shell matrix

[Praveen C]

Thanks, I will check these out.

I am solving a non-linear problem using TS. I will use -snes_mf so that jacobian action is computed by petsc using finite differences.

I am trying to use shell matrix for preconditioner P as follows.

      call MatCreateShell(PETSC_COMM_WORLD, n, n, &
                          PETSC_DETERMINE, PETSC_DETERMINE, &
                          ctx, P, ierr); CHKERRQ(ierr)
      call MatShellSetOperation(P, MATOP_MULT, ApplyPC, ierr); CHKERRQ(ierr)
      call TSSetRHSJacobian(ts, P, P, RHSJacobian, ctx, ierr); CHKERRQ(ierr)

Is ApplyPC supposed to do the following ?

subroutine ApplyPC(P, x, y, ierr)

! Compute y = P^(-1) * x

end subroutine ApplyPC

Thanks
praveen

> On 18-May-2018, at 7:23 PM, Jed Brown <jed at jedbrown.org> wrote:
> 
> See examples at the bottom of the page.
> 
> http://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/PC/PCShellSetApply.html
> 
> Praveen C <cpraveen at gmail.com> writes:
> 
>> Dear all
>> 
>> I am looking for any example code that shows how to use my own matrix-free preconditioner using a shell matrix. I am using TS to solve my problem.
>> 
>> Thanks
>> praveen