The intrinsic functions, supplied in the Fortran libraries, perform frequently used computations.
References to Fortran intrinsic functions use the same form as references to user-defined functions. For example, the following intrinsic function reference is valid:
R = 3.14159 * ABS(X-1)
This reference to the intrinsic function ABS causes the absolute
value of X-1 to be multiplied by the constant 3.14159;
the result of that calculation is assigned to the variable R.
Two methods of referencing intrinsic functions are described in the following section.