[petsc-users] How to use PETSc4py/SLEPc4py to solve an eigenvalue problem in parallel

[Jed Brown]

Mengqi Zhang <jollage at gmail.com> writes:
> It seems that the parallel running doesn't work, the elapsed time is
> roughly the same. 

http://www.mcs.anl.gov/petsc/documentation/faq.html#computers

> You see that in the process of assembling the matrix in the parallel
> case, the two cores are working according to
>
>     from  0  to  8192  on rank  0
>     from  8192  to  16384  on rank  1
>
> but in the SLEPc phase, only rank 0 is working (the print command only
> works for rank 0, but not for rank 1). 

That is just printing.  If every rank printed, you'd have a jumbled mess
of output.

Always send the output of -log_summary if you have questions about performance.

> I also tried to run the ex1.py in parallel and in serial, the
> computation times for a relative large matrix are also roughly the
> same for the two runnings, or in some cases, parallel running is even
> longer.

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