Merge pull request python-control#219 from murrayrm/fix_slycot-zero

murrayrm · web-flow · commit cab7fa04a1f3 · 2018-07-07T14:21:07.000-07:00
Fix slycot zero

Small fix of a bug that is blocking 0.8.0 release =&gt; merging without external review.
diff --git a/control/statesp.py b/control/statesp.py
@@ -525,7 +525,11 @@ def zero(self):
             out = ab08nd(self.A.shape[0], self.B.shape[1], self.C.shape[0],
                          self.A, self.B, self.C, self.D)
             nu = out[0]
-            return sp.linalg.eigvals(out[8][0:nu,0:nu], out[9][0:nu,0:nu])
+            if nu == 0:
+                return np.array([])
+            else:
+                return sp.linalg.eigvals(out[8][0:nu,0:nu], out[9][0:nu,0:nu])
+            
         except ImportError:  # Slycot unavailable. Fall back to scipy.
             if self.C.shape[0] != self.D.shape[1]:
                 raise NotImplementedError("StateSpace.zero only supports "
diff --git a/control/tests/statesp_test.py b/control/tests/statesp_test.py
@@ -42,6 +42,11 @@ def testPole(self):
 
         np.testing.assert_array_almost_equal(p, true_p)
 
+    def testEmptyZero(self):
+        """Test to make sure zero() works with no zeros in system"""
+        sys = _convertToStateSpace(TransferFunction([1], [1,2,1]))
+        np.testing.assert_array_equal(sys.zero(), np.array([]))
+
     @unittest.skipIf(not slycot_check(), "slycot not installed")
     def testMIMOZero_nonsquare(self):
         """Evaluate the zeros of a MIMO system."""
