[Dune] Error in implementing PAAMG using dune-istl

Markus Blatt markus at dr-blatt.de
Thu Dec 14 14:44:14 CET 2017


On Thu, Dec 14, 2017 at 02:15:46PM +0100, Kumar, Paras wrote:
> Unfortunately, switching to typedef Dune::Amg::CoarsenCriterion<Dune::Amg::UnSymmetricCriterion<DuneMatrixType,Dune::Amg::FirstDiagonal>
> Criterion; does not help.

Please start your program under gdb and check for which matrix entries
this happens. AFAIK the only matrix entries expected here is the
(0,0) entry of each diagonal block. That should be there right?

> 
> Another point is that for 2 process and 33 unknowns it shows,
> 
> Level 0 has 33 unknowns, 16.5 unknowns per proc (procs=2)
> 
> Probably, the distribution of indexes across processes is not happening
> properly. Do I need to somehow ensure the linking of the Matrix index set to
> the DuneComm object.

That looks distributed to me. Each process has about 16 unknowns. But
maybe I misunderstood you?

You are aware that with the default settings (coarsenTarget=2000) no
coarsening takes place here and the algorithm will simply gather the
matrix on process and solve directly. Which means more work the more
processes you employ.

Markus

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