[petsc-users] A qustion of PETSc

[w_ang_temp]

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
 
>    (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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