gsl_eigen_sample.cpp

#include <iostream>
#include <cmath>
#include <gsl/gsl_math.h>
#include <gsl/gsl_vector.h>
#include <gsl/gsl_matrix.h>
#include <gsl/gsl_eigen.h>
#include <gsl/gsl_sort_vector.h>

#define DIM 2

int main(void){
  gsl_matrix *matrix = gsl_matrix_alloc(DIM,DIM);
  gsl_eigen_symm_workspace *workspace = gsl_eigen_symm_alloc(DIM);;
  gsl_vector *eig = gsl_vector_alloc(DIM);

  gsl_matrix_set(matrix,0,0,1.);
  gsl_matrix_set(matrix,0,1,-0.5);
  gsl_matrix_set(matrix,1,0,-0.5);
  gsl_matrix_set(matrix,1,1,1.);

  gsl_eigen_symm(matrix, eig, workspace);

  for(int i=0; i<DIM; i++) std::cout << gsl_vector_get(eig,i) << std::endl;

  gsl_vector_free(eig);
  gsl_eigen_symm_free(workspace);
  gsl_matrix_free(matrix);
  return 0;
}