[petsc-users] A qustion of PETSc

[Matthew Knepley]

On Sat, May 26, 2012 at 2:22 PM, w_ang_temp <w_ang_temp at 163.com> wrote:

> Hello,Matt
>     Thanks again.
>     What you said("Use -ksp_type preonly -pc_type lu") means that I should
> use a direct solver.And I am puzzled.
>

Okay, you want to remove variables from the investigation. You say there is
a difference between
the parallel and serial solve. We do this all the time, so it is not a bug.
It is an issue of understanding.
First, take away the tolerance issues:

  -ksp_rtol 1.0e-15 -ksp_converged_reason -ksp_monitor_true_residual

and send output of the serial and parallel run.

   Matt


>     (1)I think this problem (single processor is ok and more than one are
> problematic)is typical,but I cannot
> find useful infomation both in the manual and the petsc-users.So can you
> give me some explanation for this
> phenomenon.
>     (2)When I use -pc_type lu,the error message is "Matrix format mpiaij
> does not have a built-in PETSc LU!".
>     (3)The manual says that "This approach prevents the user from the
> unexpected surprise of having a
> corrupted matrix after a linear solve"(P72).So do you mean the problem of
> mine is here?
>     (4)Generally I want to use the iterative approach other than the
> direct method.
>     As a beginne r,I have to learn more about the manual.And also I think
> an experienced senior will be a more
>  useful help for me because I have gotten stuck on this problem for more
> than a week.
>      Thanks.                                Jim
>
>
> >At 2012-05-26 20:17:42,"Matthew Knepley" <knepley at gmail.com> wrote:
>
> >Use -ksp_type preonly -pc_type lu.
>
>  >  Matt
>
>
>
>


-- 
What most experimenters take for granted before they begin their
experiments is infinitely more interesting than any results to which their
experiments lead.
-- Norbert Wiener
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