Matrix operations are very useful and common in many areas of engineering and sciences and are computationally expensive- and therefore, they are of interest to computer science.
You may have encountered matrices already, but since knowledge of matrices is not listed as a prerequisite of this course, I do not assume that this is the case. The first few sections of this chapter define what a matrix is (at least in the context of S-Q) and some of the basic matrix operations and their properties. Even if you are already familiar with matrices, you might find it useful to skim these sections in order to familiarize yourself with the notation.