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## Re: [Help-gsl] question about gsl_eigen_symm

**From**: |
Rhys Ulerich |

**Subject**: |
Re: [Help-gsl] question about gsl_eigen_symm |

**Date**: |
Thu, 1 Mar 2012 09:18:54 -0600 |

>* The manual says that, in the computation of the function " int*
>* gsl_eigen_symm (gsl matrix * A, gsl vector * eval, gsl_eigen_symm_workspace*
>* * w)", "The diagonal and lower triangular part of A are destroyed during the*
>* computation, but the strict upper triangular part is not referenced".*
>
>* Suppose I use gsl_eigen_symm to compute the eigenvalues, and then I want to*
>* modify (gsl matrix*)A and compute the eigenvalues again. After the 1st*
>* calculation, do I have to use gsl_matrix_alloc for the matrix A again before*
>* I do the 2nd calculation?*
By "destroyed" I believe the manual means "overwritten with undefined
contents". There should be no need to again use gsl_matrix_alloc your
matrix A. You should be able to re-populate matrix A's lower
triangular part (and likely the upper triangular part too) and again
call gsl_eigen_symm.
- Rhys