PROGRAM keskiarvo_testi
  IMPLICIT NONE
  REAL, DIMENSION(6) :: a
  a = (/ 1.0, -1.0, 0.5, 1.5, 2.5, 5.0 /)
  write (*,'(A,6(F7.3))') 'a: ', a
  WRITE (*,'(A,F7.3)') 'keskiarvo: ', keskiarvo(a)
  WRITE (*,'(A,F7.3)') 'keskiarvo: ', keskiarvo(a,0.0)
  WRITE (*,'(A,F7.3)') 'keskiarvo: ', &
      keskiarvo(ylaraja=3.0,alaraja=-2.0,x=a)
  WRITE (*,'(A,F7.3)') 'keskiarvo: ', keskiarvo(a,1.0,0.0)
CONTAINS
  REAL FUNCTION keskiarvo(x, alaraja, ylaraja)
    IMPLICIT NONE
    REAL, DIMENSION(:), INTENT(IN) :: x
    REAL, INTENT(IN), OPTIONAL :: alaraja, ylaraja
    REAL :: a, b
    INTEGER :: i, lkm
    a = -HUGE(a)
    b = HUGE(b)
    IF (PRESENT(alaraja)) a = alaraja
    IF (PRESENT(ylaraja)) b = ylaraja
    keskiarvo = 0
    lkm = 0
    DO i = 1, SIZE(x)
      IF (x(i) >= a .AND. x(i) <= b) THEN
        keskiarvo = keskiarvo + x(i)
        lkm = lkm + 1
      END IF
    END DO
    IF (lkm /= 0) THEN
      keskiarvo = keskiarvo/lkm
    ELSE
      keskiarvo = -HUGE(keskiarvo)
    END IF
  END FUNCTION keskiarvo
END PROGRAM keskiarvo_testi