Sage is an open-source computer algebra package. It can be downloaded for free from www.sagemath.org/ or it can be accessed directly online at the website https://sagecell.sagemath.org/. The computer computations in this book can be done in Sage, especially by those comfortable with programming in Python. In the following, we give examples of how to do some of the basic computations. Much more is possible. See www.sagemath.org/ or search the Web for other examples. Another good place to start learning Sage in general is [Bard] (there is a free online version).