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