Parametric Surface using Variable Expression

If you know parametric surface well -- or to be more specific, you know how to construct 3D surfaces using parametric equations -- it is a smooth transition from mathematical tools (such as Mathcad or Mathematica) to Grasshopper. In Mathcad, the equation for a parametric surface is:

For those who love spirograph may find it familiar. In Grasshopper, the definition looks like this:

Downloaded Grasshopper definition file: paramsurf01.ghx

In which I use Variable Expression component to hold the functions (parametric equations) for x, y, and z coordinates of the surface. Remember to set the data matching to Cross Reference so that u and v make up a 2D matrix.

And the result model of this exercise is: