# Computer Algebra Systems

A computer algebra system (CAS) is software that allows the manipulation of mathematical expressions in symbolic form. Most commonly, this is to allow the user to perform some computation. For the purposes of assessment our calculation *establishes some relevant properties* of the students' answers. These properties include

- using a predicate function to find if a single expression has a property. For example, are any of the numbers floating points?
- comparing two expressions using an answer test to compare two expressions. For example, is the student's expression equivalent to the teacher's?

A CAS is also useful for randomly generating structured mathematical objects which become parts of a question and plotting graphs of functions.

The CAS used by STACK is Maxima.

## External links

- CAS on Wikipedia
- Maxima (the CAS used by STACK)