changed named signal handling to occur in sys.sample methods. added unit tests.

sawyerbfuller · sawyerbfuller · commit 1fd68c7f7d1d · 2022-11-22T21:59:12.000-08:00
diff --git a/control/dtime.py b/control/dtime.py
@@ -47,8 +47,7 @@
 
 """
 
-from .namedio import isctime, _process_namedio_keywords
-from .iosys import ss 
+from .namedio import isctime
 from .statesp import StateSpace
 
 __all__ = ['sample_system', 'c2d']
@@ -93,10 +92,9 @@ def sample_system(sysc, Ts, method='zoh', alpha=None, prewarp_frequency=None):
     # Make sure we have a continuous time system
     if not isctime(sysc):
         raise ValueError("First argument must be continuous time system")
-    name, inputs, outputs, states, _ = _process_namedio_keywords(defaults=sysc)
-    return ss(sysc.sample(Ts,
-        method=method, alpha=alpha, prewarp_frequency=prewarp_frequency), 
-        name=name, inputs=inputs, outputs=outputs, states=states)
+
+    return sysc.sample(Ts,
+        method=method, alpha=alpha, prewarp_frequency=prewarp_frequency)
 
 
 def c2d(sysc, Ts, method='zoh', prewarp_frequency=None):
diff --git a/control/statesp.py b/control/statesp.py
@@ -1347,14 +1347,17 @@ def sample(self, Ts, method='zoh', alpha=None, prewarp_frequency=None):
         if not self.isctime():
             raise ValueError("System must be continuous time system")
 
-        sys = (self.A, self.B, self.C, self.D)
         if (method == 'bilinear' or (method == 'gbt' and alpha == 0.5)) and \
                 prewarp_frequency is not None:
             Twarp = 2 * np.tan(prewarp_frequency * Ts/2)/prewarp_frequency
         else:
             Twarp = Ts
+        sys = (self.A, self.B, self.C, self.D)
         Ad, Bd, C, D, _ = cont2discrete(sys, Twarp, method, alpha)
-        return StateSpace(Ad, Bd, C, D, Ts)
+        # get and pass along same signal names
+        _, inputs, outputs, states, _ = _process_namedio_keywords(defaults=self)
+        return StateSpace(Ad, Bd, C, D, Ts, 
+            inputs=inputs, outputs=outputs, states=states)
 
     def dcgain(self, warn_infinite=False):
         """Return the zero-frequency gain
diff --git a/control/tests/discrete_test.py b/control/tests/discrete_test.py
@@ -446,3 +446,16 @@ def test_discrete_bode(self, tsys):
         np.testing.assert_array_almost_equal(omega, omega_out)
         np.testing.assert_array_almost_equal(mag_out, np.absolute(H_z))
         np.testing.assert_array_almost_equal(phase_out, np.angle(H_z))
+    
+    def test_signal_names(self, tsys):
+        "test that signal names are preserved in conversion to discrete-time"
+        ssc = StateSpace(tsys.siso_ss1c, 
+            inputs='u', outputs='y', states=['a', 'b', 'c']) 
+        ssd = ssc.sample(0.1)
+        tfc = TransferFunction(tsys.siso_tf1c, inputs='u', outputs='y')
+        tfd = tfc.sample(0.1)
+        assert ssd.input_labels == ['u']
+        assert ssd.state_labels == ['a', 'b', 'c']
+        assert ssd.output_labels == ['y']
+        assert tfd.input_labels == ['u']
+        assert tfd.output_labels == ['y']
diff --git a/control/xferfcn.py b/control/xferfcn.py
@@ -1149,7 +1149,10 @@ def sample(self, Ts, method='zoh', alpha=None, prewarp_frequency=None):
         else:
             Twarp = Ts
         numd, dend, _ = cont2discrete(sys, Twarp, method, alpha)
-        return TransferFunction(numd[0, :], dend, Ts)
+        # get and pass along same signal names
+        _, inputs, outputs, _, _ = _process_namedio_keywords(defaults=self)
+        return TransferFunction(numd[0, :], dend, Ts,
+            inputs=inputs, outputs=outputs)
 
     def dcgain(self, warn_infinite=False):
         """Return the zero-frequency (or DC) gain
