[petsc-users] Convergence is different with different processors

[w_ang_temp]

Please do not focus any attention on ex4f. I just rename my project name to ex4f in order to use the exsiting makefile because I do not know
how use the makefile.




At 2013-02-17 02:02:15,"Hui Zhang" <mike.hui.zhang at hotmail.com> wrote:
>From my understanding of the bjacobi, it is a block Jacobi method with each block corresponding to a processor.
>What I can not understand is why you get convergence with eight blocks but divergence with four (fewer) blocks.
>Which directory is the program ex4f from?
>
>
>On Feb 16, 2013, at 6:36 PM, w_ang_temp wrote:
>
>> 
>> 
>> I use the two commands in the same project. The first is divergent while the second is convergent.
>> nohup mpiexec -n 4 ./ex4f -ksp_type bcgs -pc_type bjacobi -ksp_rtol 1.0e-5 -ksp_converged_reason >out.txt &
>> nohup mpiexec -n 8 ./ex4f -ksp_type bcgs -pc_type bjacobi -ksp_rtol 1.0e-5 -ksp_converged_reason >out.txt &
>> So what is the reason?
>> Thanks.                    Jim
>> 
>> 
>> 
>> >> 2013-02-07 13:16:51，"Matthew Knepley" <knepley at gmail.com> 写道：
>> >> On Thu, Feb 7, 2013 at 12:11 AM, w_ang_temp <w_ang_temp at 163.com> wrote:
>> >> Hello,
>> >>     I use the same project, but I find that when different number of processors is choosed,
>> >> the convergence is different. For example, when the processors are 4, it is divergent; when
>> >> the processors are 8, it is convergent.
>> >>     So what is the reason?
>> 
>> >It is likely that your preconditioner changed.
>> 
>>   > Matt
>>  
>> >>     Thanks.
>> >>                                    Jim.
>> 
>> 
>> 
>> 
>> 
>> -- 
>> 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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