Intrinsic Procedures Overview

Intrinsic procedures are functions and subroutines that are included in the Fortran library. There are four classes of these intrinsic procedures, as follows:

• Elemental procedures

  These procedures have scalar dummy arguments that can be called with scalar or array actual arguments. There are many elemental intrinsic functions and one elemental intrinsic subroutine (MVBITS).

  If the arguments are all scalar, the result is scalar. If an actual argument is array-valued, the intrinsic procedure is applied to each element of the actual argument, resulting in an array that has the same shape as the actual argument.

  If there is more than one array-valued argument, they must all have the same shape.

  Many algorithms involving arrays can now be written conveniently as a series of computations with whole arrays. For example, consider the following:

    a = b + c
    ...               ! a, b, c, and s are all arrays of similar shape
    s = sum(a)

  The above statements can replace entire DO loops.

  Consider the following:

    real, dimension (5,5) :: x,y
    . . .      ! Assign values to x
    y = sin(x) ! Pass the entire array as an argument

  In this example, since the SIN(X) function is an elemental procedure, it operates element-by-element on the array x when you pass it the name of the whole array.

• Inquiry functions

  These functions have results that depend on the properties of their principal argument, not the value of the argument (the argument value can be undefined).

• Transformational functions

  These functions have one or more array-valued dummy or actual arguments, an array result, or both. The intrinsic function is not applied elementally to an array-valued actual argument; instead it changes (transforms) the argument array into another array.

• Nonelemental procedures

  These procedures must be called with only scalar arguments; they return scalar results. All subroutines (except MVBITS) are nonelemental.

An atomic subroutine is an intrinsic subroutine that performs an action on a variable (its ATOM argument) atomically. When an atomic subroutine is executed, it is as if the subroutine were executed instantaneously without overlapping other atomic actions that might occur asynchronously.

Intrinsic procedures are invoked the same way as other procedures, and follow the same rules of argument association.

The intrinsic procedures have generic (or common) names, and many of the intrinsic functions have specific names. (Some intrinsic functions are both generic and specific.)

In general, generic functions accept arguments of more than one data type; the data type of the result is the same as that of the arguments in the function reference. For elemental functions with more than one argument, all arguments must be of the same type (except for the function MERGE).

When an intrinsic function is passed as an actual argument to a procedure, its specific name must be used, and when called, its arguments must be scalar. Some specific intrinsic functions are not allowed as actual arguments in all circumstances. The following table lists specific functions that cannot be passed as actual arguments or as targets in procedure pointer assignment statements.

Note that none of the intrinsic subroutines can be passed as actual arguments or as targets in procedure pointer assignment statements.

The A to Z Reference contains the descriptions of all intrinsics listed in alphabetical order. Each reference entry indicates whether the procedure is inquiry, elemental, transformational, or nonelemental, and whether it is a function or a subroutine.