//==============================================================================
Epetra_CrsMatrix * Poisson2dOperator::GeneratePrecMatrix() const {
// Generate a tridiagonal matrix as an Epetra_CrsMatrix
// This method illustrates how to generate a matrix that is an approximation to the true
// operator. Given this matrix, we can use any of the Aztec or IFPACK preconditioners.
// Create a Epetra_Matrix
Epetra_CrsMatrix * A = new Epetra_CrsMatrix(Copy, *map_, 3);
int NumMyElements = map_->NumMyElements();
long long NumGlobalElements = map_->NumGlobalElements64();
// Add rows one-at-a-time
double negOne = -1.0;
double posTwo = 4.0;
for (int i=0; i<NumMyElements; i++) {
long long GlobalRow = A->GRID64(i);
long long RowLess1 = GlobalRow - 1;
long long RowPlus1 = GlobalRow + 1;
if (RowLess1!=-1) A->InsertGlobalValues(GlobalRow, 1, &negOne, &RowLess1);
if (RowPlus1!=NumGlobalElements) A->InsertGlobalValues(GlobalRow, 1, &negOne, &RowPlus1);
A->InsertGlobalValues(GlobalRow, 1, &posTwo, &GlobalRow);
}
// Finish up
A->FillComplete();
return(A);
}
