int power_method(bool TransA, Epetra_RowMatrix& A, Epetra_Vector& q, Epetra_Vector& z0,
Epetra_Vector& resid, double* lambda, int niters, double tolerance, bool verbose)
{
// Fill z with random Numbers
Epetra_Vector z(z0);
// variable needed for iteration
double normz, residual;
int ierr = 1;
for(int iter = 0; iter < niters; iter++) {
z.Norm2(&normz); // Compute 2-norm of z
q.Scale(1.0/normz, z);
A.Multiply(TransA, q, z); // Compute z = A*q // SEGFAULT HAPPENS HERE
q.Dot(z, lambda); // Approximate maximum eigenvaluE
if(iter%100==0 || iter+1==niters) {
resid.Update(1.0, z, -(*lambda), q, 0.0); // Compute A*q - lambda*q
resid.Norm2(&residual);
if(verbose) cout << "Iter = " << iter << " Lambda = " << *lambda
<< " Residual of A*q - lambda*q = " << residual << endl;
}
if(residual < tolerance) {
ierr = 0;
break;
}
}
return(ierr);
}
int
powerMethod (double & lambda,
Epetra_CrsMatrix& A,
const int niters,
const double tolerance,
const bool verbose)
{
// In the power iteration, z = A*q. Thus, q must be in the domain
// of A, and z must be in the range of A. The residual vector is of
// course in the range of A.
Epetra_Vector q (A.OperatorDomainMap ());
Epetra_Vector z (A.OperatorRangeMap ());
Epetra_Vector resid (A.OperatorRangeMap ());
Epetra_Flops* counter = A.GetFlopCounter();
if (counter != 0) {
q.SetFlopCounter(A);
z.SetFlopCounter(A);
resid.SetFlopCounter(A);
}
// Initialize the starting vector z with random data.
z.Random();
double normz, residual;
int ierr = 1;
for (int iter = 0; iter < niters; ++iter)
{
z.Norm2 (&normz); // normz := ||z||_2
q.Scale (1.0/normz, z); // q := z / normz
A.Multiply(false, q, z); // z := A * q
q.Dot(z, &lambda); // lambda := dot (q, z)
// Compute the residual vector and display status output every
// 100 iterations, or if we have reached the maximum number of
// iterations.
if (iter % 100 == 0 || iter + 1 == niters)
{
resid.Update (1.0, z, -lambda, q, 0.0); // resid := A*q - lambda*q
resid.Norm2 (&residual); // residual := ||resid||_2
if (verbose)
cout << "Iter = " << iter << " Lambda = " << lambda
<< " Residual of A*q - lambda*q = " << residual << endl;
}
if (residual < tolerance) { // We've converged!
ierr = 0;
break;
}
}
return ierr;
}
