use double link list to implenment memory allocation. There won t appear maloc, new, delete, in my code. All is using freelist to find a suitable memory space.
computes the eigenvalues of a symmetric tridiagonal
* matrix T. The user may ask for all eigenvalues, all eigenvalues
in the half-open interval (VL, VU], or the IL-th through IU-th eigenvalues.
