Riemann sum model for the multivariable "monkey saddle"

This model shows the rectangular prisms (29 x 29) that make up the Riemann sum approximation to the integral of the function f(x,y) = k(x³ - 3xy²). The graph of this function exhibits a "monkey saddle."

I have also included the OpenSCAD file, which is set up so you can modify the function or parameters to produce your own model.