subroutine sort(a, n)
c
c -- shell-metzner sort for vector a
c -- figure 6.6
c     
      integer n, i, j, jump, j2, j3
      real a(1)
c
      jump = n
10    jump = jump / 2
       if (jump .eq. 0) goto 99
        j2 = n - jump
       do 30 j = 1, j2
        i = j
20      j3 = i + jump
         if (a(i) .le. a(j3)) goto 30
         call swap(a(i), a(j3))
         i = i - jump
         if (i .gt. 0) goto 20
30     continue
       goto 10
99    return
      end