Catch one additional source of mistakes

nifty6/extra.py

@@ -143,7 +143,7 @@ def _performance_check(op, pos, raise_on_fail):
         op = op @ cop
         op(pos)
         cond = [cop.count != 1]
-        lin = op(Linearization.make_var(pos, wm))
+        lin = op(2*Linearization.make_var(pos, wm))
         cond.append(cop.count != 2)
         lin.jac(pos)
         cond.append(cop.count != 3)