[petsc-users] Seq vs MPI convergence

[Barry Smith]

On Apr 14, 2013, at 5:23 PM, Jed Brown <jedbrown at mcs.anl.gov> wrote:

> Hugo Gagnon <opensource.petsc at user.fastmail.fm> writes:
> 
>> Hi,
>> 
>> I have a problem that converges fine in sequential mode but diverges
>> in MPI (other problems seem to converge fine for both modes).  I am no
>> expert in parallel solvers but, is this something I should expect?
>> I'm using BiCGSTAB with BJACOBI ILU(3).  Perhaps I'm overseeing some
>> parameters that could improve my convergences?
> 
> The most common problem is that you assemble a different operator in
> parallel.  So check that and check that you get the same answer when
> using redundant solves.
> 
>  -pc_type redundant -redundant_pc_type ilu


  See also: http://www.mcs.anl.gov/petsc/documentation/faq.html#differentiterations   and http://www.mcs.anl.gov/petsc/documentation/faq.html#kspdiverged