Welcome to Programming and Data Structures

There are two special values that can be represented by floating-point numbers you should be aware of.

The first is infinity, which is represented by the constant INFINITY. This is used to represent values that are too large to be stored in a floating-point number. Recall that doubles can store enormous values, so you are likely only to run into INFINITY if you do some math that results in an answer that approaches infinity like dividing by 0 or trying to calculate \(tan(\frac{\pi}{2})\text{.}\)

The second is Not a Number, which is represented by the constant NAN. This is used to represent values that are not real numbers, such as the result of taking the square root of a negative number. NAN is not equal to any value, including itself, so the only way to check if a value is “Not a Number” is to use the isnan function from the cmath library.

Once you have a value that is one of these special values, doing more math with it will generally just result in the same special value. Any number + INFINITY is INFINITY. NAN + a number is still NAN. So they are mostly useful as indicators that some bit of math has gone wrong. In this book we will never attempt to calculate either of these or rely on doing anything with these values. So if you ever see nan or inf as the result of outputting a floating-point number, go double check your math!