Matrix convergence.

[billy at dem.uminho.pt]

Thank you for all your help. You were right, there was a problem with the
matrix. It was supposed to be symmetric and it wasn't in only two rows.

Billy.


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

> 
>    You did not type it right -sub_pc_type lu not -pc_type lu
> 
> 
> On Fri, 3 Mar 2006, billy at dem.uminho.pt wrote:
> 
> >
> > 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.
> >>>>>
> >>>>>
> >>>>
> >>>>
> >>>
> >>>
> >>>
> >>
> >>
> >
> >
> >
> 
>