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sort.c

/* eigen/eigen_sort.c
 * 
 * Copyright (C) 1996, 1997, 1998, 1999, 2000 Gerard Jungman
 * 
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or (at
 * your option) any later version.
 * 
 * This program is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * General Public License for more details.
 * 
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
 */

/* Author:  G. Jungman, Modified: B. Gough. */

#include <config.h>
#include <stdlib.h>
#include <gsl/gsl_math.h>
#include <gsl/gsl_eigen.h>

/* The eigen_sort below is not very good, but it is simple and
 * self-contained. We can always implement an improved sort later.  */

int
gsl_eigen_symmv_sort (gsl_vector * eval, gsl_matrix * evec, 
                      gsl_eigen_sort_t sort_type)
{
  if (evec->size1 != evec->size2)
    {
      GSL_ERROR ("eigenvector matrix must be square", GSL_ENOTSQR);
    }
  else if (eval->size != evec->size1)
    {
      GSL_ERROR ("eigenvalues must match eigenvector matrix", GSL_EBADLEN);
    }
  else
    {
      const size_t N = eval->size;
      size_t i;

      for (i = 0; i < N - 1; i++)
        {
          size_t j;
          size_t k = i;

          double ek = gsl_vector_get (eval, i);

          /* search for something to swap */
          for (j = i + 1; j < N; j++)
            {
              int test;
              const double ej = gsl_vector_get (eval, j);

              switch (sort_type)
                {       
                case GSL_EIGEN_SORT_VAL_ASC:
                  test = (ej < ek);
                  break;
                case GSL_EIGEN_SORT_VAL_DESC:
                  test = (ej > ek);
                  break;
                case GSL_EIGEN_SORT_ABS_ASC:
                  test = (fabs (ej) < fabs (ek));
                  break;
                case GSL_EIGEN_SORT_ABS_DESC:
                  test = (fabs (ej) > fabs (ek));
                  break;
                default:
                  GSL_ERROR ("unrecognized sort type", GSL_EINVAL);
                }

              if (test)
                {
                  k = j;
                  ek = ej;
                }
            }

          if (k != i)
            {
              /* swap eigenvalues */
              gsl_vector_swap_elements (eval, i, k);

              /* swap eigenvectors */
              gsl_matrix_swap_columns (evec, i, k);
            }
        }

      return GSL_SUCCESS;
    }
}


int
gsl_eigen_hermv_sort (gsl_vector * eval, gsl_matrix_complex * evec, 
                      gsl_eigen_sort_t sort_type)
{
  if (evec->size1 != evec->size2)
    {
      GSL_ERROR ("eigenvector matrix must be square", GSL_ENOTSQR);
    }
  else if (eval->size != evec->size1)
    {
      GSL_ERROR ("eigenvalues must match eigenvector matrix", GSL_EBADLEN);
    }
  else
    {
      const size_t N = eval->size;
      size_t i;

      for (i = 0; i < N - 1; i++)
        {
          size_t j;
          size_t k = i;

          double ek = gsl_vector_get (eval, i);

          /* search for something to swap */
          for (j = i + 1; j < N; j++)
            {
              int test;
              const double ej = gsl_vector_get (eval, j);

              switch (sort_type)
                {       
                case GSL_EIGEN_SORT_VAL_ASC:
                  test = (ej < ek);
                  break;
                case GSL_EIGEN_SORT_VAL_DESC:
                  test = (ej > ek);
                  break;
                case GSL_EIGEN_SORT_ABS_ASC:
                  test = (fabs (ej) < fabs (ek));
                  break;
                case GSL_EIGEN_SORT_ABS_DESC:
                  test = (fabs (ej) > fabs (ek));
                  break;
                default:
                  GSL_ERROR ("unrecognized sort type", GSL_EINVAL);
                }

              if (test)
                {
                  k = j;
                  ek = ej;
                }
            }

          if (k != i)
            {
              /* swap eigenvalues */
              gsl_vector_swap_elements (eval, i, k);

              /* swap eigenvectors */
              gsl_matrix_complex_swap_columns (evec, i, k);
            }
        }

      return GSL_SUCCESS;
    }
}

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