Functions

Maple has a large library of functions for you to use.  Syntactically,
functions are a type of expression.  They have a name, a sequence of
zero or more arguments, and they return a value as a result of calling
the function. For example:

> a := -2;
a := -2
> abs(a);
2
> a;
-2

The result of taking the absolute value of "a" is returned as the result
of the function abs(...).  The variable "a" itself is not modified as a
side effect.  If you wanted to change the value of the variable, you
would use:

> a := abs(a);
a := 2

Functions are a special case of procedures.  Later in this document you
will learn how to construct your own functions and procedures.