[petsc-users] Inquiry about the preconditioner setup of KSP.

[Xiaodong Liu]

Thanks, Jed !

Xiaodong Liu, PhD
X: Computational Physics Division
Los Alamos National Laboratory
P.O. Box 1663,
Los Alamos, NM 87544
505-709-0534


On Tue, Mar 3, 2020 at 8:46 PM Jed Brown <jed at jedbrown.org> wrote:

> Xiaodong Liu <xliu29 at ncsu.edu> writes:
>
> > Thanks  a lot.  I am transferring  a dense matrix from Julia to Petsc.
> > I will check this.
> > In addition, could you please show me where is
> >
> >  Where is the subroutine for the GMRES solver, namely,
> >   ierr=(*KSP->ops->solve)(ksp);
>
> $ git grep KSPSolve_GMRES
> src/docs/tex/manual/developers.tex:\item Names of implementations of class
> functions should begin with the function name, an underscore, and the name
> of the implementation, for example, \lstinline{KSPSolve_GMRES()}.
> src/ksp/ksp/impls/gmres/gmres.c:PetscErrorCode KSPSolve_GMRES(KSP ksp)
> src/ksp/ksp/impls/gmres/gmres.c:  ksp->ops->solve                        =
> KSPSolve_GMRES;
>
>
> >
> > Xiaodong Liu, PhD
> > X: Computational Physics Division
> > Los Alamos National Laboratory
> > P.O. Box 1663,
> > Los Alamos, NM 87544
> > 505-709-0534
> >
> >
> > On Tue, Mar 3, 2020 at 8:21 PM Jed Brown <jed at jedbrown.org> wrote:
> >
> >> Is it possible that Julia is transferring the matrix to PETSc as a dense
> >> matrix (storing the nonzeros) instead of preserving sparsity?  If you
> >> store the zeros, then ILU will be allowed to fill those entries, thereby
> >> becoming LU.
> >>
> >> Xiaodong Liu <xliu29 at ncsu.edu> writes:
> >>
> >> > I am trying to use Julia to call Petsc.
> >> > 1) First, I run the built-in example ex2.c
> >> >
> >>
> https://www.mcs.anl.gov/petsc/petsc-current/src/ksp/pc/examples/tutorials/ex2.c.html
> >> >
> >> > For this case,  I tried KSPGMRES , initial zero solution and
> different PC
> >> > (LU, ILU, ICC, JACOBI). And they work as expected.
> >> >
> >> >  75: KSPSetType(ksp,KSPGMRES);
> >> >  76: KSPSetInitialGuessNonzero(ksp,PETSC_FALSE);
> >> >  87: KSPGetPC(ksp,&pc);
> >> >  88: PCSetType(pc,PCICC);
> >> >
> >> > 2) Second, I tried to call KSP from Julia using the same matrix and
> right
> >> > hand side as ex2.c . A wrapper has been written to call Petsc code
> from
> >> > Julia. After I transfer matrix to from Julia to Petsc, I checked the
> >> matrix
> >> > and preconditioner matrix in the context of Petsc. These two matrices
> are
> >> > right. For no preconditioner,Jacobi precontioner and LU, the residual
> for
> >> > Julia version is same as that of original Petsc one for every
> iteration.
> >> > However, for ILU preconditioner, the residual for Julia is alwaysthe
> same
> >> > as the LU one. This is not expected. For both Julia and original Petsc
> >> > version, I checked the PC type inside the subroutine PCSetType and the
> >> > types are correct, namely ilu.I am trying to dig into the source code
> to
> >> > check how the preconditioner is interacting with GMRES.
> >> >
> >> > Where is the subroutine for the GMRES solver, namely,
> >> >  ierr=(*KSP->ops->solve)(ksp);
> >> >
> >> > Or do you have any suggestions?
> >> >
> >> > Thanks,
> >> >
> >> > Xiaodong Liu, PhD
> >> > X: Computational Physics Division
> >> > Los Alamos National Laboratory
> >> > P.O. Box 1663,
> >> > Los Alamos, NM 87544
> >> > 505-709-0534
> >>
>
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