c naok method ----------------------------------------------------------------->
c /////////////////////////////////////////////////////////////////////>
      subroutine next_naok(id_flag, naok, id, val, nx, ny)

      integer naok, id
      integer nx,ny
      real    val(nx,ny)
      logical id_flag(nx)
      
      if (id_flag(id)) then
         write(*,*) "this id(", id ,") is already used"
      else
         id_flag(id) = .true.

         naok = naok + 1
         val(1, naok) = id
      endif

c use this after checked that your src is correct
c      naok = naok + 1
c      val(1, naok) = id

      return 
      end
c /////////////////////////////////////////////////////////////////////>

c initialize id_flag
c /////////////////////////////////////////////////////////////////////>
      subroutine init_id_flag(id_flag, nx)

      integer nx
      logical id_flag(nx)

      integer id

      do id = 1, nx
         id_flag(id) = .false.
      enddo

      return
      end
c /////////////////////////////////////////////////////////////////////>