This program diagonalizes a spin hamiltonian (defined in mod_hamiltonian) and
prints its eigenvalues and eigenvectors. It also calculates the transition energies 
and the expectation values of Sx, Sy, Sz and S^2.
The input is given by two namelists in a file called "input".
- &parameters, containing:
 the spin of the system S, which defines the dimension of the problem (2*S+1);
 the Hamiltonian variables defining the axial and transverse anisotropies, D and E, respectively;
 and an external magnetic field that defines the Zeeman energy (in Tesla), B.
- &Bloop, containing values for a loop over applied magnetic fields:
 Bmax, the maximum value of the applied field (starting with the value B above);
 npoints, defining the number of field points to calculate in the interval [B,Bmax);
 comp, which defines the component of the field to be varied (1 - x, 2 - y, 3 - z).