int
main (int argc, char *argv[])
{
// These "using" statements make the code a bit more concise.
using std::cout;
using std::endl;
int ierr = 0, i;
// If Trilinos was built with MPI, initialize MPI, otherwise
// initialize the serial "communicator" that stands in for MPI.
#ifdef EPETRA_MPI
MPI_Init (&argc,&argv);
Epetra_MpiComm Comm (MPI_COMM_WORLD);
#else
Epetra_SerialComm Comm;
#endif
const int MyPID = Comm.MyPID();
const int NumProc = Comm.NumProc();
// We only allow (MPI) Process 0 to write to stdout.
const bool verbose = (MyPID == 0);
const int NumGlobalElements = 100;
if (verbose)
cout << Epetra_Version() << endl << endl;
// Asking the Epetra_Comm to print itself is a good test for whether
// you are running in an MPI environment. However, it will print
// something on all MPI processes, so you should remove it for a
// large-scale parallel run.
cout << Comm << endl;
if (NumGlobalElements < NumProc)
{
if (verbose)
cout << "numGlobalBlocks = " << NumGlobalElements
<< " cannot be < number of processors = " << NumProc << endl;
std::exit (EXIT_FAILURE);
}
// Construct a Map that puts approximately the same number of rows
// of the matrix A on each processor.
Epetra_Map Map (NumGlobalElements, 0, Comm);
// Get update list and number of local equations from newly created Map.
int NumMyElements = Map.NumMyElements();
std::vector<int> MyGlobalElements(NumMyElements);
Map.MyGlobalElements(&MyGlobalElements[0]);
// NumNz[i] is the number of nonzero elements in row i of the sparse
// matrix on this MPI process. Epetra_CrsMatrix uses this to figure
// out how much space to allocate.
std::vector<int> NumNz (NumMyElements);
// We are building a tridiagonal matrix where each row contains the
// nonzero elements (-1 2 -1). Thus, we need 2 off-diagonal terms,
// except for the first and last row of the matrix.
for (int i = 0; i < NumMyElements; ++i)
if (MyGlobalElements[i] == 0 || MyGlobalElements[i] == NumGlobalElements-1)
NumNz[i] = 2; // First or last row
else
NumNz[i] = 3; // Not the (first or last row)
// Create the Epetra_CrsMatrix.
Epetra_CrsMatrix A (Copy, Map, &NumNz[0]);
//
// Add rows to the sparse matrix one at a time.
//
std::vector<double> Values(2);
Values[0] = -1.0; Values[1] = -1.0;
std::vector<int> Indices(2);
const double two = 2.0;
int NumEntries;
for (int i = 0; i < NumMyElements; ++i)
{
if (MyGlobalElements[i] == 0)
{ // The first row of the matrix.
Indices[0] = 1;
NumEntries = 1;
}
else if (MyGlobalElements[i] == NumGlobalElements - 1)
{ // The last row of the matrix.
Indices[0] = NumGlobalElements-2;
NumEntries = 1;
}
else
{ // Any row of the matrix other than the first or last.
Indices[0] = MyGlobalElements[i]-1;
Indices[1] = MyGlobalElements[i]+1;
NumEntries = 2;
}
ierr = A.InsertGlobalValues(MyGlobalElements[i], NumEntries, &Values[0], &Indices[0]);
assert (ierr==0);
// Insert the diagonal entry.
ierr = A.InsertGlobalValues(MyGlobalElements[i], 1, &two, &MyGlobalElements[i]);
assert(ierr==0);
}
// Finish up. We can call FillComplete() with no arguments, because
// the matrix is square.
ierr = A.FillComplete ();
assert (ierr==0);
// Parameters for the power method.
const int niters = NumGlobalElements*10;
const double tolerance = 1.0e-2;
//
// Run the power method. Keep track of the flop count and the total
// elapsed time.
//
Epetra_Flops counter;
A.SetFlopCounter(counter);
Epetra_Time timer(Comm);
double lambda = 0.0;
ierr += powerMethod (lambda, A, niters, tolerance, verbose);
double elapsedTime = timer.ElapsedTime ();
double totalFlops =counter.Flops ();
// Mflop/s: Million floating-point arithmetic operations per second.
double Mflop_per_s = totalFlops / elapsedTime / 1000000.0;
if (verbose)
cout << endl << endl << "Total Mflop/s for first solve = "
<< Mflop_per_s << endl<< endl;
// Increase the first (0,0) diagonal entry of the matrix.
if (verbose)
cout << endl << "Increasing magnitude of first diagonal term, solving again"
<< endl << endl << endl;
if (A.MyGlobalRow (0)) {
int numvals = A.NumGlobalEntries (0);
std::vector<double> Rowvals (numvals);
std::vector<int> Rowinds (numvals);
A.ExtractGlobalRowCopy (0, numvals, numvals, &Rowvals[0], &Rowinds[0]); // Get A(0,0)
for (int i = 0; i < numvals; ++i)
if (Rowinds[i] == 0)
Rowvals[i] *= 10.0;
A.ReplaceGlobalValues (0, numvals, &Rowvals[0], &Rowinds[0]);
}
//
// Run the power method again. Keep track of the flop count and the
// total elapsed time.
//
lambda = 0.0;
timer.ResetStartTime();
counter.ResetFlops();
ierr += powerMethod (lambda, A, niters, tolerance, verbose);
elapsedTime = timer.ElapsedTime();
totalFlops = counter.Flops();
Mflop_per_s = totalFlops / elapsedTime / 1000000.0;
if (verbose)
cout << endl << endl << "Total Mflop/s for second solve = "
<< Mflop_per_s << endl << endl;
#ifdef EPETRA_MPI
MPI_Finalize() ;
#endif
return ierr;
}
