Computes all eigenvalues and eigenvectors of a real symmetric matrix a,
! which is of size n by n, stored in a physical np by np array.
! On output, elements of a above the diagonal are destroyed.
! d returns the eigenvalues of a in its first n elements.
! v is a matrix with the same logical and physical dimensions as a,
! whose columns contain, on output, the normalized eigenvectors of a.
! nrot returns the number of Jacobi rotations that were required.
! Please notice that the eigenvalues are not ordered on output.
! If the sorting is desired, the addintioal routine "eigsrt"
! can be invoked to reorder the output of jacobi.
