[petsc-users] How to speed up geometric multigrid

Jed Brown jedbrown at mcs.anl.gov
Thu Oct 3 16:43:13 CDT 2013

Michele Rosso <mrosso at uci.edu> writes:

> Barry,
> thank you, I hope to be able to fix this bug.
> On a side note, I took a look at ex34.c and I noticed that the nullspace 
> is removed not only from the matrix but from the rhs as well. Why is 
> this done?

You need the right hand side to be consistent if you want to be able to
say that your residual is small.
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