nsymgreg.cc

ARPACK is a collection of Fortran77 subroutines designed to solve large scale eigenvalue problems.

/*
   ARPACK++ v1.0 8/1/1997
   c++ interface to ARPACK code.

   MODULE NSymGReg.cc.
   Example program that illustrates how to solve a real
   nonsymmetric generalized eigenvalue problem in regular mode
   using the ARNonSymGenEig class.

   1) Problem description:

      In this example we try to solve A*x = x*lambda in regular mode,
      where A and B are derived from the finite element discretization
      of the 1-dimensional convection-diffusion operator
                         (d^2u / dx^2) + rho*(du/dx)
      on the interval [0,1] with zero Dirichlet boundary conditions
      using linear elements.

   2) Data structure used to represent matrix A:

      When using ARNonSymGenEig, the user is required to provide some
      classes that contain as member functions the matrix-vector
      products w = OPv = inv(B)*A*v and w = B*v. 
      In this example, NonSymGenProblemA is a class that contains a 
      member function, MultOPv(v,w), that takes a vector v and returns 
      the product OPv in w. It also contains an object, B, that stores
      matrix B data. The product Bv is performed by MultMv, a member
      function of B.

   3) Included header files:

      File             Contents
      -----------      -------------------------------------------
      ngenprba.h       The NonSymGenProblemA class definition.
      argnsym.h        The ARNonSymGenEig class definition.
      nsymgsol.h       The Solution function.

   5) ARPACK Authors:

      Richard Lehoucq
      Kristyn Maschhoff
      Danny Sorensen
      Chao Yang
      Dept. of Computational & Applied Mathematics
      Rice University
      Houston, Texas
*/

#include "ngenprba.h"
#include "nsymgsol.h"
#include "argnsym.h"


template<class T>
void Test(T type)
{

  // Creating Eig A*x = lambda*B*x.

  NonSymGenProblemA<T> P(100); // n = 100.

  // Defining what we need: the four eigenvectors with largest magnitude.
  // P.MultOPv is the function that performs the product w <- OPv.
  // P.B.MultMv is the function that performs the product w <- Bv.

  ARNonSymGenEig<T, NonSymGenProblemA<T>, NonSymMatrixD<T> >
    dprob(P.A.ncols(), 4, &P, &NonSymGenProblemA<T>::MultOPv,
          &P.B, &NonSymMatrixD<T>::MultMv);

  // Finding eigenvalues and eigenvectors.

  dprob.FindEigenvectors();

  // Printing solution.

  Solution(P.A, P.B, dprob);

} // Test.


main()
{

  // Solving a double precision problem with n = 100.

  Test((double)0.0);

  // Solving a single precision problem with n = 100.

  Test((float)0.0);

} // main