set default dt to be 0 instead of None.

sawyerbfuller · bnavigator · commit 86401d66e0f3 · 2020-12-31T00:37:20.000+01:00
diff --git a/control/statesp.py b/control/statesp.py
@@ -72,9 +72,9 @@
 # Define module default parameter values
 _statesp_defaults = {
     'statesp.use_numpy_matrix': False,  # False is default in 0.9.0 and above
-    'statesp.default_dt': None,
+    'statesp.default_dt': 0,
     'statesp.remove_useless_states': True,
-    }
+}
 
 
 def _ssmatrix(data, axis=1):
@@ -974,7 +974,7 @@ def dcgain(self):
         return np.squeeze(gain)
 
     def is_static_gain(self):
-         """True if and only if the system has no dynamics, that is, 
+         """True if and only if the system has no dynamics, that is,
          if A and B are zero. """
          return not np.any(self.A) and not np.any(self.B)
 
diff --git a/control/xferfcn.py b/control/xferfcn.py
@@ -71,7 +71,7 @@
 
 # Define module default parameter values
 _xferfcn_defaults = {
-    'xferfcn.default_dt': None}
+    'xferfcn.default_dt': 0}
 
 class TransferFunction(LTI):
 
@@ -1597,6 +1597,20 @@ def _clean_part(data):
 
     return data
 
+def _isstaticgain(num, den):
+    """returns true if and only if all of the numerator and denominator 
+    polynomials of the (possibly MIMO) transfer funnction are zeroth order, 
+    that is, if the system has no dynamics. """
+    num, den = _clean_part(num), _clean_part(den)
+    for m in range(len(num)):
+        for n in range(len(num[m])):
+            if len(num[m][n]) > 1: 
+                return False
+    for m in range(len(den)):
+        for n in range(len(den[m])):
+            if len(den[m][n]) > 1: 
+                return False
+    return True
 
 # Define constants to represent differentiation, unit delay
 TransferFunction.s = TransferFunction([1, 0], [1], 0)
