Matrix convergence.

[Matthew Knepley]

billy at dem.uminho.pt writes:

      Are you sure you have -pc_type bjacobi -sub_pc_type lu?

          Matt

> 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.
>> >>>
>> >>>
>> >>
>> >>
>> >
>> >
>> >
>> 
>> 
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-- 
"Failure has a thousand explanations. Success doesn't need one" -- Sir Alec Guiness