Matrix convergence.

[billy at dem.uminho.pt]

This is what I get:

[0]PETSC ERROR: MatLUFactorSymbolic() line 2159 in src/mat/interface/matrix.c
[0]PETSC ERROR: No support for this operation for this object type!
[0]PETSC ERROR: Matrix type mpiaij  symbolic LU!
[0]PETSC ERROR: PCSetUp_LU() line 252 in src/ksp/pc/impls/factor/lu/lu.c
[0]PETSC ERROR: PCSetUp() line 798 in src/ksp/pc/interface/precon.c
[0]PETSC ERROR: KSPSetUp() line 234 in src/ksp/ksp/interface/itfunc.c
[0]PETSC ERROR: KSPSolve() line 334 in src/ksp/ksp/interface/itfunc.c


Quoting Barry Smith <bsmith at mcs.anl.gov>:

> 
>    Run the parallel PETSc job with -ksp_type gmres -ksp_gmres_restart 200
> -sub_pc_type lu
> 
> 
> On Fri, 3 Mar 2006, billy at dem.uminho.pt wrote:
> 
> > Hi,
> >
> > I tried to solve the 18x18 matrix with laspack and the results are the
> following:
> >
> > Solver: GMRES, Preconditioning: NULL, Iterations: 500, Residual: 6.16E-2
> > Solver: GMRES, Preconditioning: SSOR, Iterations: 500, Residual: 6.57E-2
> > Solver: GMRES, Preconditioning: ILU, ERROR
> >
> > Solver: BiCGSTAB, Preconditioning: NULL, Iterations: 101, Residual:
> 8.88E-7
> > Solver: BiCGSTAB, Preconditioning: SSOR, Iterations: 36, Residual:
> 9.87E-7
> > Solver: BiCGSTAB, Preconditioning: ILU, ERROR
> >
> >
> > Billy.
> >
> >
> > Quoting Barry Smith <bsmith at mcs.anl.gov>:
> >
> >>
> >>    Billy,
> >>
> >>     Most likely there is something wrong with the matrix being
> >> generated. I would first look at the matrix entries and make
> >> sure they make sense. Then I would solve the linear systems
> >> with a direct solver -pc_type lu (on one processor and make
> >> sure the solutions are reasonable and your simulation has
> >> "correct" answers).
> >>
> >>    It is possible the parallel matrix generation is wrong,
> >>
> >>    Barry
> >>
> >>
> >> On Thu, 2 Mar 2006, billy at dem.uminho.pt wrote:
> >>
> >>>
> >>> Hi,
> >>>
> >>>
> >>> I have been testing my parallel implementation with a 2D case. I have
> used
> >> the
> >>> following grids with 2 and 4 processes: 4x4, 10x10, 16x16 and 18x18.
> >>>
> >>> It works for the first three (max. number of iterations to converge
> aprox.
> >> 70)
> >>> but when I increase to 18x18 the matrix does not converge. I have
> increased
> >> the
> >>> maximum number of iterations and I have used GMRES, BiCGSTAB with
> >>> preconditioners ASM, JACOBI, etc.
> >>>
> >>> With KSPType = GMRES and PCType = ASM:
> >>> Number of iterations: 500 Residual: +1.420471E-01
> >>>
> >>> With KSPType = GMRES and PCType = JACOBI:
> >>> Number of iterations: 500 Residual: +2.351882E-02
> >>>
> >>> With KSPType = BCGS and PCType = ASM:
> >>> Number of iterations: 136 Residual: +3.911446E+04
> >>>
> >>> With KSPType = BCGS and PCType = NULL:
> >>> Number of iterations: 157 Residual: +3.254728E+03
> >>>
> >>> Is it normal that the convergence detiorates so much with such a slight
> >> increase
> >>> in the dimension of the matrix? Is there any optimization parameter that
> I
> >> may
> >>> be missing?
> >>>
> >>>
> >>> Billy.
> >>>
> >>>
> >>
> >>
> >
> >
> >
> 
>