This demo graphs a density function ρ(x, y, z) for a rectangular region
and then finds the center of mass of that region. Changing "rhoMin"
(estimated minimum value of ρ(x, y, z) and "rhoMax" estimated maximum
value of ρ(x, y, z)) is optional. Doing so will improve the coloring of
the graph (cyan at "rhoMin", red at "rhoMax").