def doPartC(Ustar, phi_num, Ud, nx, ny, xmin, xmax, ymin, ymax, DO_PLOTS):
    ' coordinates of centers '
    dx = ((xmax - xmin) / nx)
    dy = ((ymax - ymin) / ny)
    ' calcuates the new gradient'
    Gphi = numpy.gradient(phi_num, dx, dy)
    ' recover Ud, new '
    Unew = map(operator.sub, Ustar, Gphi)
    if (DO_PLOTS == 1):
        do_plots_c(Ud, Unew)
    return 0
coordinates of centers
def doPartC(Ustar, phi_num, Ud, nx, ny, xmin, xmax, ymin, ymax, DO_PLOTS):
    '  '
    dx = ((xmax - xmin) / nx)
    dy = ((ymax - ymin) / ny)
    ' calcuates the new gradient'
    Gphi = numpy.gradient(phi_num, dx, dy)
    ' recover Ud, new '
    Unew = map(operator.sub, Ustar, Gphi)
    if (DO_PLOTS == 1):
        do_plots_c(Ud, Unew)
    return 0