update use/computation of sys._isstatic()

murrayrm · murrayrm · commit d99ac619e92f · 2025-02-01T22:33:57.000-08:00
diff --git a/control/nlsys.py b/control/nlsys.py
@@ -1668,7 +1668,7 @@ def ufun(t):
         return U[..., idx-1] * (1. - dt) + U[..., idx] * dt
 
     # Check to make sure this is not a static function
-    if nstates == 0:            # No states => map input to output
+    if sys._isstatic():
         # Make sure the user gave a time vector for evaluation (or 'T')
         if t_eval is None:
             # User overrode t_eval with None, but didn't give us the times...
diff --git a/control/xferfcn.py b/control/xferfcn.py
@@ -225,6 +225,7 @@ def __init__(self, *args, **kwargs):
                     break
             if not static:
                 break
+        self._static = static
 
         defaults = args[0] if len(args) == 1 else \
             {'inputs': num.shape[1], 'outputs': num.shape[0]}
@@ -1279,12 +1280,8 @@ def _isstatic(self):
         """returns True if and only if all of the numerator and denominator
         polynomials of the (possibly MIMO) transfer function are zeroth order,
         that is, if the system has no dynamics. """
-        for list_of_polys in self.num, self.den:
-            for row in list_of_polys:
-                for poly in row:
-                    if len(poly) > 1:
-                        return False
-        return True
+        # Check done at initialization
+        return self._static
 
     # Attributes for differentiation and delay
     #
