; show_sys $sys_id
;
; display graphically a spin-system


; get spin list
  set ss = $_
  set l = $sys[$ss]
  set num = (head($l))
  set aa = (head(tail($l)))
  set l = (tail(tail($l)))

; count and find min and max
  set p = ($spin[head($l)])
  set min = (head($p))   set max = $min
  set p = (head(tail($l)))   set lp = (tail(tail($l)))
  while ($p s! " ")
     set p = (head($spin[$p]))
     if ($min > $p) set min = $p
     if ($max < $p) set max = $p
     set p = (head($lp))   set lp = (tail($lp))
  endwhile

; draw boxes
  set max1 = (ptoi($max,2,1))
  set max2 = (ptoi($max,2,2))
  set min1 = (ptoi($min,2,1))
  set min2 = (ptoi($min,2,2))
  set p = (head($l))  set lp = (tail($l))
  while ($p s! " ")
     set p = (head($spin[$p]))
     set p1 = (ptoi($p,2,1))     set p2 = (ptoi($p,2,2))
     showline $p2 $min1 $p2 $max1
     showline $min2 $p1 $max2 $p1
     set p = (head($lp))   set lp = (tail($lp))
  endwhile




