fix issue with multiplying MIMO LTI system by scalar (#1078)

murrayrm · web-flow · commit 8b6d041e2135 · 2024-12-10T16:04:08.000-08:00
diff --git a/control/frdata.py b/control/frdata.py
@@ -261,14 +261,20 @@ def __init__(self, *args, **kwargs):
 
         # create interpolation functions
         if smooth:
+            # Set the order of the fit
+            if self.omega.size < 2:
+                raise ValueError("can't smooth with only 1 frequency")
+            degree = 3 if self.omega.size > 3 else self.omega.size - 1
+
             self.ifunc = empty((self.fresp.shape[0], self.fresp.shape[1]),
                                dtype=tuple)
             for i in range(self.fresp.shape[0]):
                 for j in range(self.fresp.shape[1]):
                     self.ifunc[i, j], u = splprep(
                         u=self.omega, x=[real(self.fresp[i, j, :]),
                                          imag(self.fresp[i, j, :])],
-                        w=1.0/(absolute(self.fresp[i, j, :]) + 0.001), s=0.0)
+                        w=1.0/(absolute(self.fresp[i, j, :]) + 0.001),
+                        s=0.0, k=degree)
         else:
             self.ifunc = None
 
@@ -392,7 +398,12 @@ def __add__(self, other):
 
         # Convert the second argument to a frequency response function.
         # or re-base the frd to the current omega (if needed)
-        other = _convert_to_frd(other, omega=self.omega)
+        if isinstance(other, (int, float, complex, np.number)):
+            other = _convert_to_frd(
+                other, omega=self.omega,
+                inputs=self.ninputs, outputs=self.noutputs)
+        else:
+            other = _convert_to_frd(other, omega=self.omega)
 
         # Check that the input-output sizes are consistent.
         if self.ninputs != other.ninputs:
diff --git a/control/tests/lti_test.py b/control/tests/lti_test.py
@@ -350,3 +350,21 @@ def test_subsys_indexing(fcn, outdx, inpdx, key):
             np.testing.assert_almost_equal(
                 subsys_fcn.frequency_response(omega).response,
                 subsys_chk.frequency_response(omega).response)
+
+
+@slycotonly
+@pytest.mark.parametrize("op", [
+    '__mul__', '__rmul__', '__add__', '__radd__', '__sub__', '__rsub__'])
+@pytest.mark.parametrize("fcn", [ct.ss, ct.tf, ct.frd])
+def test_scalar_algebra(op, fcn):
+    sys_ss = ct.rss(4, 2, 2)
+    match fcn:
+        case ct.ss:
+            sys = sys_ss
+        case ct.tf:
+            sys = ct.tf(sys_ss)
+        case ct.frd:
+            sys = ct.frd(sys_ss, [0.1, 1, 10])
+
+    scaled = getattr(sys, op)(2)
+    np.testing.assert_almost_equal(getattr(sys(1j), op)(2), scaled(1j))
diff --git a/control/xferfcn.py b/control/xferfcn.py
@@ -634,11 +634,11 @@ def __mul__(self, other):
         from .statesp import StateSpace
 
         # Convert the second argument to a transfer function.
-        if isinstance(other, StateSpace):
+        if isinstance(other, (StateSpace, np.ndarray)):
             other = _convert_to_transfer_function(other)
-        elif isinstance(other, (int, float, complex, np.number, np.ndarray)):
-            other = _convert_to_transfer_function(other, inputs=self.ninputs,
-                                                  outputs=self.noutputs)
+        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)
         if not isinstance(other, TransferFunction):
             return NotImplemented
 
@@ -681,8 +681,8 @@ def __rmul__(self, other):
 
         # Convert the second argument to a transfer function.
         if isinstance(other, (int, float, complex, np.number)):
-            other = _convert_to_transfer_function(other, inputs=self.ninputs,
-                                                  outputs=self.ninputs)
+            # Multiply by a scaled identity matrix (transfer function)
+            other = _convert_to_transfer_function(np.eye(self.noutputs) * other)
         else:
             other = _convert_to_transfer_function(other)
 
@@ -723,9 +723,8 @@ def __truediv__(self, other):
         """Divide two LTI objects."""
 
         if isinstance(other, (int, float, complex, np.number)):
-            other = _convert_to_transfer_function(
-                other, inputs=self.ninputs,
-                outputs=self.ninputs)
+            # Multiply by a scaled identity matrix (transfer function)
+            other = _convert_to_transfer_function(np.eye(self.ninputs) * other)
         else:
             other = _convert_to_transfer_function(other)
 
