Clojure and Incanter are powerful, flexible tools, but they're not the only ones we have. We may have some analyses already implemented in another system, for instance, and we'd like to use them even though we're using Clojure everywhere else.
Mathematica (http://www.wolfram.com/mathematica/) is one of those tools. It's a software environment produced by Wolfram Research. It does complex mathematics and graphing, among many other things. It's a powerful tool made more powerful and customizable, thanks to its programming language.
R (http://www.r-project.org/) is another such tool. It's an open source system that specializes in statistical computing. It is also a programming language, and thanks to an active user community, there are a lot of contributed packages for almost any statistical task.
Both of these systems are powerful and complex in their own right, and we won't be able to go into how to use them or their features in this chapter. However, if you already have some...