Merge pull request #590 from juanodecc/step_info_improve_undershoot

bnavigator · web-flow · commit ce4c2b604a66 · 2021-03-25T12:01:24.000+01:00
Change step_info undershoot percentage calculation
diff --git a/control/tests/timeresp_test.py b/control/tests/timeresp_test.py
@@ -301,17 +301,17 @@ def mimo_ss_step_matlab(self):
                          'SteadyStateValue': -0.5394},
                          {'RiseTime': 0.0000, # (*)
                          'SettlingTime': 3.4000,
-                         'SettlingMin': -0.1034,
+                         'SettlingMin': -0.4350,  # (*)
                          'SettlingMax': -0.1485,
                          'Overshoot': 132.0170,
-                         'Undershoot': 79.222, # 0. in MATLAB
+                         'Undershoot': 0.,
                          'Peak': 0.4350,
                          'PeakTime': .2,
                          'SteadyStateValue': -0.1875}]]
-                         # (*): MATLAB gives 0.4 here, but it is unclear what
-                         # 10% and 90% of the steady state response mean, when
-                         # the step for this channel does not start a 0 for
-                         # 0 initial conditions
+                         # (*): MATLAB gives 0.4 for RiseTime and -0.1034 for
+                         # SettlingMin, but it is unclear what 10% and 90% of
+                         # the steady state response mean, when the step for
+                         # this channel does not start a 0.
         return T
 
     @pytest.fixture
diff --git a/control/timeresp.py b/control/timeresp.py
@@ -923,11 +923,11 @@ def step_info(sysdata, T=None, T_num=None, yfinal=None,
                 else:
                     overshoot = 0
 
-                # Undershoot
-                y_us = (sgnInf * yout).min()
-                dy_us = np.abs(y_us)
-                if dy_us > 0:
-                    undershoot = np.abs(100. * dy_us / InfValue)
+                # Undershoot : InfValue and undershoot must have opposite sign
+                y_us_index = (sgnInf * yout).argmin()
+                y_us = yout[y_us_index]
+                if (sgnInf * y_us) < 0:
+                    undershoot = (-100. * y_us / InfValue)
                 else:
                     undershoot = 0
 
