[petsc-users] questions about snes ex3.c

[Xiangdong]

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.

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
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