Multivariable Function Lesson

This set of things provide examples of graphs of mulitvariable functions. This page is meant to complement the paper "3D Printed Manipulatives in a Multivariable Calculus Classroom" which will appear in PRIMUS.
The three functions used here are:
- f(x,y) = x^2+y^2
- f(x,y) = xy
- f(x,y) = 2xe^(-x^2-y^2)