[petsc-users] A qustion of PETSc

[w_ang_temp]

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 carefulanalysis 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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