Merge pull request #647 from vincentchoqueuse/fix_damp_bug_dlti_system

bnavigator · web-flow · commit 18976c1eabe5 · 2021-08-19T11:46:59.000+02:00
fix damp method for discrete time systems with a negative real-valued pole
diff --git a/control/lti.py b/control/lti.py
@@ -159,7 +159,7 @@ def damp(self):
         poles = self.pole()
 
         if isdtime(self, strict=True):
-            splane_poles = np.log(poles)/self.dt
+            splane_poles = np.log(poles.astype(complex))/self.dt
         else:
             splane_poles = poles
         wn = absolute(splane_poles)
diff --git a/control/tests/lti_test.py b/control/tests/lti_test.py
@@ -70,6 +70,14 @@ def test_damp(self):
         np.testing.assert_almost_equal(sys_dt.damp(), expected_dt)
         np.testing.assert_almost_equal(damp(sys_dt), expected_dt)
 
+        #also check that for a discrete system with a negative real pole the damp function can extract wn and zeta.
+        p2_zplane = -0.2
+        sys_dt2 = tf(1, [1, -p2_zplane], dt)
+        wn2, zeta2, p2 = sys_dt2.damp()
+        p2_splane = -wn2 * zeta2 + 1j * wn2 * np.sqrt(1 - zeta2**2)
+        p2_zplane = np.exp(p2_splane * dt)
+        np.testing.assert_almost_equal(p2, p2_zplane)
+        
     def test_dcgain(self):
         sys = tf(84, [1, 2])
         np.testing.assert_allclose(sys.dcgain(), 42)
