PRESENT

 PRESENT (opt-argument)

 Class:  Inquiry function - Generic

 Returns whether or not an optional dummy argument is present (has
 an associated actual argument).

 Example:

 Consider the following:

 SUBROUTINE CHECK (X, Y)
   REAL X, Z
   REAL, OPTIONAL :: Y
   ...
   IF (PRESENT (Y)) THEN
     Z = Y
   ELSE
      Z = X * 2
   END IF
 END         
 ...
 CALL CHECK (15.0, 12.0)      ! Causes B to be set to 12.0
 CALL CHECK (15.0)            ! Causes B to be set to 30.0