[petsc-users] A qustion of PETSc

[Jed Brown]

Yes, a good linear solver involves a suitable choice of Krylov method and
preconditioner.

On Mon, Jun 4, 2012 at 7:37 AM, w_ang_temp <w_ang_temp at 163.com> wrote:

> Hello
>      As I become familiar with PETSc, I make a conclusion about the
> question and hope that it is right.
>      In order to get satisfactory results when solving a linear system
> with KSP, the Krylov space methods
> are typically used in conjunction with a preconditioner. So the user
> should  select the effective Krylov
> method(such as cg) and preconditioner(such as jacobi) for this linear
> system Ax=b. Or it maybe not
> convergence.
>      Thanks.
>                               Jim
>
>
> >At 2012-05-26 23:05:26,w_ang_temp <w_ang_temp at 163.com> wrote:
>
>  >Hello, Matt
> >     The results of the parallel and the serial  are identical by the
> "-ksp_rtol 1.0e-15 -ksp_converged_reason -ksp_monitor_true_residual".
> >     I will make a careful analysis of these  parameters next day
> because it is late night here now.
> >     Thanks again.
> Jim
> >在 2012-05-26 22:26:20，"Matthew Knepley" <knepley at gmail.com> 写道：
>
> >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
>
>
>
>
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