BugFix: pole of stateless StateSpace object is empty array

roryyorke · roryyorke · commit c84debb49c14 · 2016-12-28T20:13:59.000+02:00
diff --git a/control/statesp.py b/control/statesp.py
@@ -399,7 +399,7 @@ def freqresp(self, omega):
     def pole(self):
         """Compute the poles of a state space system."""
 
-        return eigvals(self.A)
+        return eigvals(self.A) if self.states else np.array([])
 
     def zero(self):
         """Compute the zeros of a state space system."""
diff --git a/control/tests/statesp_test.py b/control/tests/statesp_test.py
@@ -378,6 +378,12 @@ def testPole(self):
                         self.assertTrue(abs(z) < 1)
 
 
+    def testPoleStatic(self):
+        """Regression: pole() of static gain is empty array"""
+        np.testing.assert_array_equal(np.array([]),
+                                      StateSpace([],[],[],[[1]]).pole())
+
+
 def suite():
    return unittest.TestLoader().loadTestsFromTestCase(TestStateSpace)
 
