## Chapter 8. Three-dimensional plots

This chapter covers

• Basics of three-dimensional plots
• Generating surface and contour plots
• Plotting data from a file

In all the plots that we’ve seen so far, we plotted one variable (y) as a function of another one (x). But what if we want to show how some quantity depends on two independent variables? In other words, how can we best visualize a single “output” variable as a function of two “input” variables?

One approach we can take distinguishes the two input variables into the actual independent variable (x) and one parameter. We can then generate a plot showing y as a function of x, for different values of the parameter, as shown in figure 8.1. There, we plot the function

`f(x,a) = 0.5*(x**4)/4! + a*(x**2)/2 ...`

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