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
     IMPLICIT NONE
     INTEGER, INTENT(IN) :: n        ! in interface
     REAL, INTENT(IN) :: k,x         ! in interface
     REAL, INTENT(OUT) :: sum        ! in interface
     REAL, SAVE :: cool_time
      ...
    END SUBROUTINE expsum            ! in interface

The explicit INTERFACE for this routine is given by the statements:

    INTERFACE ! for EXTERNAL procedure
     SUBROUTINE expsum( n, k, x, sum )
      INTEGER, INTENT(IN) :: n
      REAL, INTENT(IN) :: k,x
      REAL, INTENT(OUT)  :: sum
     END SUBROUTINE expsum
    END INTERFACE

This could be included in the declarations part of any other program unit which calls expsum.

Interfaces are not needed for internal (or module) procedures.

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