DG_SMOOTH

        DG_SMOOTH
        Smoothes an image using the Conjugate Gradient Algorithm.
        (Author: Didier GIRARD, Groupe d'Astrophysique)

    The  smoothed  image  is  the  equilibrium  state  of  a  thin  flexible
    plate  constrained  to  pass near each height datum by a spring attached
    between it and the plate.  The smoothing is controled by the  "Smoothing
    Parameter" P :
                    P = ( plate stiffness) / ( springs stiffness)
    A low value for P (0.001) means high fidelity to the original  data  and
    should  be used for high signal to noise ratios.  If the data are noisy,
    use higher values of P (0.1 to 10).   The  algorithm  is  iterative  and
    needs  a  work  space equal to 3 input maps.  It usually converges in 10
    iterations, and can be restarted if you save the work files.  Timing  is
    of  the order of 2 seconds of microVAX II CPU time for a 128 by 128 map.
    It takes into account blanked pixels properly.