fix matrix_formula_period()

graph_tools/utils.py

@@ -201,7 +201,7 @@ def _init_():
       for i in range(len(seen)):
         if seen[i] == r:
           return (i + shift,
-            [None]*shift + (seen if vectors else [min(1, (l*v)[0, 0]) for v in seen ]))
+            [None]*shift + (seen if vectors else [ int(l*v != 0) for v in seen ]))
 
       seen.append(r)
       r = to_zero_one(A*r)