BugFix: fix Python 2.7 failure.

roryyorke · roryyorke · commit 4a74cc559468 · 2016-12-28T20:13:25.000+02:00
On Python 2.7, the special case "all states useless" in
_remove_useless_states resulted in A=[[0]] (and similarly for B and C).

The special case is no longer needed, since empty A, B, C matrices can
be handled.  numpy.delete does the right thing w.r.t. matrix
sizes (e.g., deleting all columns of a nxm matrix gives an nx0 matrix).

Added test for this.
diff --git a/control/statesp.py b/control/statesp.py
@@ -146,7 +146,7 @@ def __init__(self, *args):
         if self.states != B.shape[0]:
             raise ValueError("A and B must have the same number of rows.")
         if self.states != C.shape[1]:
-            raise ValueError("A and C C must have the same number of columns.")
+            raise ValueError("A and C must have the same number of columns.")
         if self.inputs != B.shape[1]:
             raise ValueError("B and D must have the same number of columns.")
         if self.outputs != C.shape[0]:
@@ -180,17 +180,10 @@ def _remove_useless_states(self):
                 useless.append(i)
 
         # Remove the useless states.
-        if all(useless == range(self.states)):
-            # All the states were useless.
-            self.A = zeros((1, 1))
-            self.B = zeros((1, self.inputs))
-            self.C = zeros((self.outputs, 1))
-        else:
-            # A more typical scenario.
-            self.A = delete(self.A, useless, 0)
-            self.A = delete(self.A, useless, 1)
-            self.B = delete(self.B, useless, 0)
-            self.C = delete(self.C, useless, 1)
+        self.A = delete(self.A, useless, 0)
+        self.A = delete(self.A, useless, 1)
+        self.B = delete(self.B, useless, 0)
+        self.C = delete(self.C, useless, 1)
 
         self.states = self.A.shape[0]
         self.inputs = self.B.shape[1]
diff --git a/control/tests/statesp_test.py b/control/tests/statesp_test.py
@@ -254,10 +254,14 @@ def test_scalarStaticGain(self):
         np.testing.assert_array_equal(np.diag([2,3]),g6.D)
 
     def test_matrixStaticGain(self):
-        """Regression: can we create a scalar static gain?"""
+        """Regression: can we create matrix static gains?"""
         d1 = np.matrix([[1,2,3],[4,5,6]])
         d2 = np.matrix([[7,8],[9,10],[11,12]])
         g1=StateSpace([],[],[],d1)
+
+        # _remove_useless_states was making A = [[0]]
+        self.assertEqual((0,0), g1.A.shape)
+
         g2=StateSpace([],[],[],d2)
         g3=StateSpace([],[],[],d2.T)
 
@@ -271,6 +275,19 @@ def test_matrixStaticGain(self):
         np.testing.assert_array_equal(block_diag(d1,d2),h4.D)
 
 
+    def test_remove_useless_states(self):
+        """Regression: _remove_useless_states gives correct ABC sizes"""
+        g1 = StateSpace(np.zeros((3,3)),
+                        np.zeros((3,4)),
+                        np.zeros((5,3)),
+                        np.zeros((5,4)))
+        self.assertEqual((0,0), g1.A.shape)
+        self.assertEqual((0,4), g1.B.shape)
+        self.assertEqual((5,0), g1.C.shape)
+        self.assertEqual((5,4), g1.D.shape)
+        self.assertEqual(0, g1.states)
+
+
     def test_BadEmptyMatrices(self):
         """Mismatched ABCD matrices when some are empty"""
         self.assertRaises(ValueError,StateSpace, [1], [],  [],  [1])
