Procedure Interfaces

For EXTERNAL procedures it is possible to provide an explicit interface for a procedure. Consider:

    SUBROUTINE expsum( n, k, x, sum )! in interface
     USE KIND_VALS:ONLY long
     IMPLICIT NONE
     INTEGER, INTENT(IN) :: n        ! in interface
     REAL(long), INTENT(IN) :: k,x   ! in interface
     REAL(long), INTENT(OUT) :: sum  ! in interface
     REAL(long), SAVE :: cool_time
      sum = 0.0
      DO i = 1, n
       sum = sum + exp(-i*k*x)
      END DO
    END SUBROUTINE expsum            ! in interface

The explicit INTERFACE for this routine is given by the statements which appear in the declarations part of any program unit that calls expsum:

    INTERFACE           ! for EXTERNAL procedures
     SUBROUTINE expsum( n, k, x, sum )
      USE KIND_VALS:ONLY long
      INTEGER, INTENT(IN) :: n
      REAL(long), INTENT(IN) :: k,x
      REAL(long), INTENT(OUT)  :: sum
     END SUBROUTINE expsum
    END INTERFACE

Interfaces replace any EXTERNAL statements and are not needed for internal (or module) procedures.

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