[petsc-users] questions about snes ex3.c

[Matthew Knepley]

On Wed, Apr 2, 2014 at 8:23 AM, Xiangdong <epscodes at gmail.com> wrote:

> Hello everyone,
>
> I have two quick questions about src/snes/examples/tutorials/ex3.c.
>
> 1) In line 150-151, why do we need to call MatSeqAIJSetPreallocation
> before MatMPIAIJSetPreallocation? I found that without the seqaij call, the
> program crashed. However, the mat J we want to create is the mpiaij.
>

One is used in serial, the other in parallel. Really, you can just call


http://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/Mat/MatXAIJSetPreallocation.html

   Matt


> 2) In line 390-397, it sets the values of the residue function at the
> boundary. Where do these values come from? In other words, I am not clear
> about ff[0]=xx[0] and ff[xs+xm-1] = xx[xs+xm-1] - 1.0;
>
> Thank you.
>
> Xiangdong
>



-- 
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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