[Trilinos-Users] vectors on overlapped maps

[erhan turan]

Hello everyone,

I have a question regarding to vector overlapped maps. Attached code is a
modification of example 9 in didasko/epetra folder. A vector is created
with an overlapping map.

What to expect as a norm value on two cores is 2. what you get is 0 ! Of
course, this was an example on Import and Export methods - there you are
also playing win Epetra_CombineMode.

My question is, why is "0" the result?  And also, should we always use
Export and Import methods to deal overlapped maps? So, it is not safe to
use such a naive approach even if the map is created carefully.

Regards,

Erhan Turan
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#include "Epetra_ConfigDefs.h"
#ifdef HAVE_MPI
#include "mpi.h"
#include "Epetra_MpiComm.h"
#else
#include "Epetra_SerialComm.h"
#endif
#include "Epetra_Map.h"
#include "Epetra_Vector.h"
#include "Epetra_Export.h"

int main(int argc, char *argv[]) {

#ifdef HAVE_MPI
  MPI_Init(&argc, &argv);
  Epetra_MpiComm Comm(MPI_COMM_WORLD);
#else
  Epetra_SerialComm Comm;
#endif

  int NumGlobalElements = 4; // global dimension of the problem

  int NumMyElements; // local nodes
  Epetra_IntSerialDenseVector MyGlobalElements;

  if( Comm.MyPID() == 0 ) {
    NumMyElements = 3;
    MyGlobalElements.Size(NumMyElements);
    MyGlobalElements[0] = 0;
    MyGlobalElements[1] = 1;
    MyGlobalElements[2] = 2;
  } else {
    NumMyElements = 3;
    MyGlobalElements.Size(NumMyElements);
    MyGlobalElements[0] = 1;
    MyGlobalElements[1] = 2;
    MyGlobalElements[2] = 3;
  }

  // create a map
  Epetra_Map Map(-1,MyGlobalElements.Length(),
		 MyGlobalElements.Values(),0, Comm);

  // create a vector based on map
  Epetra_Vector x(Map);

/*
  for( int i=0 ; i<NumMyElements ; ++i ){
       x[i] = 1.0;
  }
*/

x.PutScalar(1.0);

double myNorm;

x.Norm2(&myNorm);


cout<<"norm is ="<<myNorm<< " over " << x.GlobalLength()<< " elements"<<endl;


#ifdef HAVE_MPI
  MPI_Finalize();
#endif

  return(EXIT_SUCCESS);

}