BugFix: allow minreal on static gain StateSpace objects

roryyorke · roryyorke · commit fb1e90510b99 · 2016-08-12T19:01:29.000+02:00
Do this by only calling Slycot's tb01pd for non-static systems.
diff --git a/control/statesp.py b/control/statesp.py
@@ -471,18 +471,22 @@ def feedback(self, other=1, sign=-1):
     def minreal(self, tol=0.0):
         """Calculate a minimal realization, removes unobservable and
         uncontrollable states"""
-        try:
-            from slycot import tb01pd
-            B = empty((self.states, max(self.inputs, self.outputs)))
-            B[:,:self.inputs] = self.B
-            C = empty((max(self.outputs, self.inputs), self.states))
-            C[:self.outputs,:] = self.C
-            A, B, C, nr = tb01pd(self.states, self.inputs, self.outputs,
-                                    self.A, B, C, tol=tol)
-            return StateSpace(A[:nr,:nr], B[:nr,:self.inputs],
-                              C[:self.outputs,:nr], self.D)
-        except ImportError:
-            raise TypeError("minreal requires slycot tb01pd")
+        if self.states:
+            try:
+                from slycot import tb01pd
+                B = empty((self.states, max(self.inputs, self.outputs)))
+                B[:,:self.inputs] = self.B
+                C = empty((max(self.outputs, self.inputs), self.states))
+                C[:self.outputs,:] = self.C
+                A, B, C, nr = tb01pd(self.states, self.inputs, self.outputs,
+                                     self.A, B, C, tol=tol)
+                return StateSpace(A[:nr,:nr], B[:nr,:self.inputs],
+                                  C[:self.outputs,:nr], self.D)
+            except ImportError:
+                raise TypeError("minreal requires slycot tb01pd")
+        else:
+                return StateSpace(self)
+
 
     # TODO: add discrete time check
     def returnScipySignalLTI(self):
diff --git a/control/tests/statesp_test.py b/control/tests/statesp_test.py
@@ -297,6 +297,17 @@ def test_BadEmptyMatrices(self):
         self.assertRaises(ValueError,StateSpace, [],  [],  [1], [1])
         self.assertRaises(ValueError,StateSpace, [1], [1], [1], [])
 
+
+    def test_minrealStaticGain(self):
+        """Regression: minreal on static gain was failing"""
+        g1 = StateSpace([],[],[],[1])
+        g2 = g1.minreal()
+        np.testing.assert_array_equal(g1.A, g2.A)
+        np.testing.assert_array_equal(g1.B, g2.B)
+        np.testing.assert_array_equal(g1.C, g2.C)
+        np.testing.assert_array_equal(g1.D, g2.D)
+
+
 class TestRss(unittest.TestCase):
     """These are tests for the proper functionality of statesp.rss."""
 
