  By considering that the distribution of measured light along any
galactocentric radius of an elliptical galaxy can be well represented by a
R^{1/n} Sersic law, we propose in this paper a ``discrete ordenate'' method,
which, for any value of n, allows an explicit expression for the luminous
density, rho(r), to be found that can be numerically evaluated to any required
precision. Once we have this semi-analytical expression for the spatial
density, rho(r), the mass distribution, M(r), the potential, phi(r), and the
velocity dispersions, sigma_s^2(r), in the space and in the observational
plane, sigma_p^2(R), can be computed in a straightforward manner.
