Ok send the code to petsc-maint at mcs.anl.gov
Barry
On Nov 6, 2012, at 1:56 PM, Chung-Kan Huang <ckhuangf at gmail.com> wrote:
> Barry,
>
> We have tried tiny tol and lu but the problem is still there. It doesn't
> make sense to us that this problem is expected and common in iterative
> solvers instead we think this might be caused by some mistakes we made when
> we setup the ksp, pc or even the linear system.
>
>
>
>
>
> On Sat, Oct 27, 2012 at 6:07 PM, Barry Smith <bsmith at mcs.anl.gov> wrote:
>
>
> PETSc, by default, using iterative solvers which only solve the problem
> within a certain accuracy. You can control this accuracy by using -ksp_rtol
> tol where for example you could pick tol = 1.0e-12 You can also use a
> direct solver
> -pc_type lu Run with -ksp_monitor_true_residual -ksp_converged_reason to
> see if the linear solver is solving to the requested accuracy.
>
> Barry
>
> On Oct 27, 2012, at 3:46 PM, Chung-Kan Huang <ckhuangf at gmail.com> wrote:
>
> > Hi,
> >
> > I am solving a linear system A * X = B that sometime contains A_{I,I} != 0
> > A_{I,J} = 0. where I!=J and B_I = 0. so I would expect X_i to be perfect
> > zero not some tiny small value. The same linear system is solved by other
> > solvers but they gave zero for aforementioned situation even the system is
> > fair large to our applications. I have tried several configurations in
> > PETSc hoping that problem can be solved but all attempts failed. I wonder
> > if someone can give me some pointers that help to solve this issue. Thanks,
> >
> > Chung-Kan
> >
> >
> >
> > --
> > Cheers
> >
> >
>
>
>
>
> --
> Cheers
>
>
