c ...  This is the interface routine called by IDL
       subroutine vecmin(argc, argv)
       integer*4 argc, argv(*), j
       j = loc(argc)
       call vecmin1(%val(argv(1)), %val(argv(2)), %val(argv(3)),
     &   %val(argv(4)), %val(argv(5)))
       end

c ...  This is the routine which does the work.
c ...  The arguments are defined exactly the same as in the
c ...  call_external procedure call in IDL
       subroutine vecmin1(a, na, x, nx, b)
       integer*4 na, nx
       real*4 a(na), b(nx)
       integer*4 x(nx), i
       do i = 1, nx
         a(x(i)) = min(a(x(i)), b(i))
       end do
       end