fix: preserve signal names in scalar LTI ops

marko1olo · marko1olo · commit a63671ff4958 · 2026-06-07T19:26:55.000+04:00
diff --git a/control/statesp.py b/control/statesp.py
@@ -555,7 +555,10 @@ def fmt_matrix(matrix, name):
     # Negation of a system
     def __neg__(self):
         """Negate a state space system."""
-        return StateSpace(self.A, self.B, -self.C, -self.D, self.dt)
+        return StateSpace(
+            self.A, self.B, -self.C, -self.D, self.dt,
+            inputs=self.input_labels, outputs=self.output_labels,
+            states=self.state_labels)
 
     # Addition of two state space systems (parallel interconnection)
     def __add__(self, other):
@@ -645,7 +648,10 @@ def __mul__(self, other):
             A, C = self.A, self.C
             B = self.B * other
             D = self.D * other
-            dt = self.dt
+            return StateSpace(
+                A, B, C, D, self.dt,
+                inputs=self.input_labels, outputs=self.output_labels,
+                states=self.state_labels)
 
         elif isinstance(other, np.ndarray):
             other = np.atleast_2d(other)
@@ -706,7 +712,10 @@ def __rmul__(self, other):
             # Just multiplying by a scalar; change the input
             B = other * self.B
             D = other * self.D
-            return StateSpace(self.A, B, self.C, D, self.dt)
+            return StateSpace(
+                self.A, B, self.C, D, self.dt,
+                inputs=self.input_labels, outputs=self.output_labels,
+                states=self.state_labels)
 
         elif isinstance(other, np.ndarray):
             other = np.atleast_2d(other)
diff --git a/control/tests/namedio_test.py b/control/tests/namedio_test.py
@@ -59,6 +59,40 @@ def test_named_ss():
         "<StateSpace random: ['u1'] -> ['y1', 'y2']>"
 
 
+@pytest.mark.parametrize(
+    "sys",
+    [
+        ct.ss(
+            [[-1, 0], [0, -2]], [[1, 0], [0, 1]],
+            [[1, 0], [0, 1]], [[0, 0], [0, 0]],
+            inputs=['e1', 'e2'], outputs=['u1', 'u2'],
+            states=['x1', 'x2'], name='plant'),
+        ct.tf(
+            [[[1], [2]], [[3], [4]]],
+            [[[1, 1], [1, 2]], [[1, 3], [1, 4]]],
+            inputs=['e1', 'e2'], outputs=['u1', 'u2'], name='plant'),
+    ],
+)
+@pytest.mark.parametrize(
+    "operation",
+    [
+        lambda sys: -sys,
+        lambda sys: sys * 2,
+        lambda sys: 2 * sys,
+        lambda sys: ct.negate(sys),
+        lambda sys: ct.series(sys, 2),
+        lambda sys: ct.series(2, sys),
+    ],
+)
+def test_named_scalar_operations_preserve_signal_names(sys, operation):
+    result = operation(sys)
+
+    assert result.input_labels == sys.input_labels
+    assert result.output_labels == sys.output_labels
+    if isinstance(sys, ct.StateSpace):
+        assert result.state_labels == sys.state_labels
+
+
 # List of classes that are expected
 fun_instance = {
     ct.rss: (ct.NonlinearIOSystem, ct.StateSpace, ct.StateSpace),
diff --git a/control/xferfcn.py b/control/xferfcn.py
@@ -554,7 +554,9 @@ def __neg__(self):
         for i in range(self.noutputs):
             for j in range(self.ninputs):
                 num[i, j] *= -1
-        return TransferFunction(num, self.den, self.dt)
+        return TransferFunction(
+            num, self.den, self.dt,
+            inputs=self.input_labels, outputs=self.output_labels)
 
     def __add__(self, other):
         """Add two LTI objects (parallel connection)."""
@@ -620,8 +622,13 @@ def __mul__(self, other):
         if isinstance(other, (StateSpace, np.ndarray)):
             other = _convert_to_transfer_function(other)
         elif isinstance(other, (int, float, complex, np.number)):
-            # Multiply by a scaled identity matrix (transfer function)
-            other = _convert_to_transfer_function(np.eye(self.ninputs) * other)
+            num = deepcopy(self.num_array)
+            for i in range(self.noutputs):
+                for j in range(self.ninputs):
+                    num[i, j] *= other
+            return TransferFunction(
+                num, self.den, self.dt,
+                inputs=self.input_labels, outputs=self.output_labels)
         if not isinstance(other, TransferFunction):
             return NotImplemented
 
@@ -669,8 +676,13 @@ def __rmul__(self, other):
 
         # Convert the second argument to a transfer function.
         if isinstance(other, (int, float, complex, np.number)):
-            # Multiply by a scaled identity matrix (transfer function)
-            other = _convert_to_transfer_function(np.eye(self.noutputs) * other)
+            num = deepcopy(self.num_array)
+            for i in range(self.noutputs):
+                for j in range(self.ninputs):
+                    num[i, j] *= other
+            return TransferFunction(
+                num, self.den, self.dt,
+                inputs=self.input_labels, outputs=self.output_labels)
         else:
             other = _convert_to_transfer_function(other)
 
