Hi,
I experience the following problem. With the following elementary code :
void Quadriques::dir_courb_principal(gsl_vector *courb, gsl_matrix *dir)
{
gsl_matrix * M = gsl_matrix_alloc(2,2) ;
gsl_matrix_set(M, 0, 0, 2. * this->coef[0]) ;
gsl_matrix_set(M, 0, 1, this->coef[1]) ;
gsl_matrix_set(M, 1, 0, this->coef[1]) ;
gsl_matrix_set(M, 1, 1, 2. * this->coef[2]) ;
gsl_eigen_symmv_workspace * w = gsl_eigen_symmv_alloc (2) ;
// Compute eigenvectors and eigenvalues
gsl_eigen_symmv (M, courb, dir, w) ;
//gsl_eigen_gensymmv_sort (courb, dir, GSL_EIGEN_SORT_VAL_DESC) ;
gsl_matrix_free(M) ;
}
called with the following coefs array : [5, -7, 2] (that is, I compute
the eigenvalues/
vectors of the following matrix :
10 -7
-7 2
I get the following eigenvectors :
0.834841 0.550491
-0.550491 0.834841
whereas Maple (and my hand computations) give :
Of cours, the sign does not matter, but ...... x and y's are
exchanged !!!!!!
How is it that such problem occurs ?
Thanks in advance.
Alexandra Bac
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