Re: [Help-gsl] question about gsl_eigen_symm

[Rhys Ulerich]

> 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