8.5.1.3 Elemental Procedures

An elemental procedure is a user-defined procedure that is a restricted form of pure procedure. An elemental procedure can be passed an array, which is acted upon one element at a time. Elemental procedures are a feature of Fortran 95.

To specify an elemental procedure, use the prefix ELEMENTAL in a FUNCTION or SUBROUTINE statement.

An explicit interface must be visible to the caller of an ELEMENTAL procedure.

For functions, the result must be scalar; it cannot have the POINTER attribute.

Dummy arguments have the following restrictions:

• They must be scalar.
  
  
• They cannot have the POINTER attribute.
  
  
• They (or their subobjects) cannot appear in a specification expression, except as an argument to one of the intrinsic functions BIT_SIZE, LEN, KIND, or the numeric inquiry functions.
  
  
• They cannot be *.
  
  
• They cannot be dummy procedures.

If the actual arguments are all scalar, the result is scalar. If the actual arguments are array-valued, the values of the elements (if any) of the result are the same as if the function or subroutine had been applied separately, in any order, to corresponding elements of each array actual argument.

Elemental procedures are pure procedures and all rules that apply to pure procedures also apply to elemental procedures.

Examples

Consider the following:

MIN (A, 0, B)             ! A and B are arrays of shape (S, T)

In this case, the elemental reference to the MIN intrinsic function is an array expression whose elements have the following values:

MIN (A(I,J), 0, B(I,J)), I = 1, 2, ..., S, J = 1, 2, ..., T

For More Information:

• On the FUNCTION statement, see Section 8.5.2.
  
  
• On the SUBROUTINE statement, see Section 8.5.3.
  
  
• On determining when procedures require explicit interfaces, see Section 8.9.1.
  
  
• On pure procedures and the PURE prefix, see Section 8.5.1.2.
  
  
• On optional arguments, see Section 8.8.1.