[dune-pdelab] Problems with MPI

[Christian Engwer]

Hi Timothy,

just a guess...

As you are now using MPI, DUNE will work in the parallel mode. This
means in particular, that your meshes are now by default bound to the
MPI_Comm_World communicator. As you want to run many independent
samples in parallel, you have to make sure to choose the correct
communicator.

Ciao
Christian

On Wed, Jan 13, 2016 at 04:54:19PM +0000, Dodwell, Timothy wrote:
> Dear All,
> 
> 
> I am running the latest release of PDELab on a Mac OX 10.10.5. I am implementing a multilevel monte carlo algorithm which is wrapped around a general model (in this case linear elasticity which uses SEQ_CG_AMG_SSOR for the solver.)
> 
> 
> All works well and is tested in series. I have now tried to simply parallelise a for loop which computes a number of independent samples (see below). getSample is a function which returns a quantity of interest from my model and nproc is the number of processors.
> 
> 
> When I do this, all processors with rank from 0 to (nproc -2) return values of NaN. If I run the code on 1 processor all works ok.
> 
> Thanks in advance for your help!
> 
> Tim
> 
> 
> int numSamples = N[L] / nproc + 1; // Compute number of samples on each processor (rounding up)
> 
> 
> double * Ytmp = new double[numSamples];
> 
> 
> 
> double * Yroot = NULL;
> 
> 
> if (rank == 0){ Yroot = new double[numSamples * nproc];    }
> 
> 
> 
> for (int i = 0; i < numSamples; i++){    Ytmp[i] = getSample(L,z);    }
> 
> 
> 
> MPI_Gather(Ytmp,numSamples,MPI_DOUBLE,Yroot,numSamples,MPI_DOUBLE,0,MPI_COMM_WORLD);
> 
> 
> 
> Dr Tim Dodwell
> 
> Lecturer in Engineering Mathematics
> 
> Rm 221 - Harrison Building
> 
> College of Engineering, Mathematics & Physical Sciences
> 
> University of Exeter
> 
> Exeter
> 
> Devon
> 
> EX4 4PY
> 
> 
> mail: t.dodwell(at)exeter.ac.uk
> 
> tel: +44 (0)1392 725899
> 
> mob: +44 (0)7745 622870
> 
> web: http://emps.exeter.ac.uk/engineering/staff/td336
> 
> Papers and Pre-prints: @Research-Gate<https://www.researchgate.net/profile/Timothy_Dodwell>
> 
> Citations: @Google-Scholar<https://scholar.google.co.uk/citations?user=lPpjRfUAAAAJ&hl=en>
> 
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-- 
Prof. Dr. Christian Engwer 
Institut für Numerische und Angewandte Mathematik
Fachbereich Mathematik und Informatik der Universität Münster
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