Matrix convergence.

[Barry Smith]

   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.
>
>