From mboxrd@z Thu Jan  1 00:00:00 1970
From: "Varghese John" <vjohn111@hotmail.com>
To: gsl-discuss@sources.redhat.com
Subject: Eigen value problem
Date: Wed, 19 Dec 2001 13:20:00 -0000
Message-id: <F77Bv7QqsQIkQsB4i0c0000fa21@hotmail.com>
X-SW-Source: 2001/msg00539.html

Hi,
I am having problems with the following program.
trying to get eigen values for the 2x2 matrix, and the program hangs?

--it works fine for a 3x3 matrix!

thanks.
vj
-----------------------------------------------
#include <gsl/gsl_eigen.h>
#include <stdio.h>
#include <math.h>

#define TestSize 2

void GetEigen1();
void GetEigenvaluesForSymmMat(  gsl_matrix * m, int mSize, gsl_vector * v);


int main(){
	GetEigen1();
	return(0);
}

void GetEigen1(){

  int i;
  int j;
  int x;

  gsl_matrix * m = gsl_matrix_alloc(TestSize, TestSize);
  gsl_matrix_set_zero(m);


  /* matrix = ((1, 2), (2, 1)) */

  gsl_matrix_set(m, 0, 0, 1.0);
  gsl_matrix_set(m, 0, 1, 2.0);
  gsl_matrix_set(m, 1, 0, 2.0);
  gsl_matrix_set(m, 1, 1, 1.0);



  /* matrix = ((4, 1, 1), (1, 2, 2), (1, 2, 9)) */
  /*
  gsl_matrix_set(m, 0, 0, 4.0);
  gsl_matrix_set(m, 0, 1, 1.0);
  gsl_matrix_set(m, 0, 2, 1.0);
  gsl_matrix_set(m, 1, 0, 1.0);
  gsl_matrix_set(m, 1, 1, 2.0);
  gsl_matrix_set(m, 1, 2, 2.0);
  gsl_matrix_set(m, 2, 0, 1.0);
  gsl_matrix_set(m, 2, 1, 2.0);
  gsl_matrix_set(m, 2, 2, 9.0);
  */


  printf("The Input Matrix: \n");
  for (i = 0; i < TestSize; i++){
	  for (j = 0; j <TestSize; j++){
      printf("%6.4g \t", gsl_matrix_get (m, i, j));
	  }
    printf("\n");
  }
  printf("\n");

  //use this vector to store the eigen values.
  gsl_vector *v=gsl_vector_alloc(TestSize);
    GetEigenvaluesForSymmMat( m, TestSize, v);
    printf("The EigenValues : \n");

  //print the result
    for (x = 0; x < TestSize; x++)
     {
        printf("eigenvalue = %g\n", gsl_vector_get(v, x));
      }
}


//This function computes the eigen values of a symmetric block
//and returns the ordered eigen values in the vector v.

void GetEigenvaluesForSymmMat(  gsl_matrix * m, int mSize, gsl_vector * v) {

  gsl_vector *eval = gsl_vector_alloc (mSize);
    gsl_vector_set_zero(eval);
  gsl_matrix *evec = gsl_matrix_alloc (mSize, mSize);
    gsl_matrix_set_zero(evec);
  gsl_eigen_symmv_workspace * w =
    gsl_eigen_symmv_alloc (mSize);

  gsl_eigen_symmv (m, eval, evec, w);

  gsl_eigen_symmv_free(w);

  gsl_eigen_symmv_sort (eval, evec, GSL_EIGEN_SORT_ABS_DESC);

  gsl_vector_memcpy(v, eval);

}




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