1. The functioncompute the eigenvalues of a A, return the ordered (from largest to smallest) eigenvalues, with a maximum of n iterations, untill it satisfies some error estimate less than Tol.
2. The error is get by compute the second norm of the difference of diagonal elements of A-A0;
3. It uses the simplest QR algorithm.It tests the input matrix for symmetry. 
4. The return value of function qrfunction.c is the total number of iterations. 
5. the program compares the eigenvalues with the value get by gsl buildi-in functions.