[Trilinos-Users] Replicate Serial Vectors

[Michael A Heroux]

Ammar,

Here is a simple example that illustrates one way to replicate a vector on a
parallel machine.  I hope you find it useful.

Mike

#include "Epetra_MpiComm.h"
#include "Epetra_Map.h"
#include "Epetra_LocalMap.h"
#include "Epetra_Vector.h"
#include "Epetra_Import.h"
#include "Epetra_IntSerialDenseVector.h"
int main(int argc, char *argv[])
{
    // init mpi
    int size, rank;
    MPI_Init(&argc,&argv);
    MPI_Comm_size(MPI_COMM_WORLD, &size);
    MPI_Comm_rank(MPI_COMM_WORLD, &rank);
    Epetra_MpiComm Comm(MPI_COMM_WORLD);

    int lenX = 5;  // The length of the vector on each processor.

    Epetra_LocalMap localMap(lenX, 0, Comm); // This map has GIDs replicated
on each processor.

    // Now build source map.  It will have GIDs on PE 0 only.

    int lenX0 = 0;
    if(Comm.MyPID() == 0) lenX0= lenX;
    Epetra_IntSerialDenseVector myGIDs(lenX0);
    for (int i=0; i<lenX0; i++) myGIDs[i] = i;
    Epetra_Map map0(-1, lenX0, myGIDs.Values(), 0, Comm);

    // Now build source vector

    Epetra_Vector x0(map0);
    if (Comm.MyPID()==0) x0.SetLabel("Source Vector"); else x0.SetLabel("");
    for (int i=0; i<lenX0; i++) x0[i] = (double) (i+1)*(i+1);
    cout << x0 << endl;

    // Build import object will get the values from x0 and bring them to all
processors.

    Epetra_Import importer(localMap, map0);

    // Build replicated vector, do import and finish.

    Epetra_Vector x(localMap); // This is our target vector.
    x.Import(x0, importer, Insert);
    if (Comm.MyPID()==0) x.SetLabel("Replicated Vector"); else
x.SetLabel("");

    cout << x << endl;

    // finalize mpi
    MPI_Finalize();
    return(0);
}