Add MIMO-SISO add for TF

sdahdah · sdahdah · commit 508bc8b9dbd4 · 2024-12-19T11:20:28.000-05:00
diff --git a/control/tests/xferfcn_test.py b/control/tests/xferfcn_test.py
@@ -113,9 +113,28 @@ def test_constructor_double_dt(self):
 
     def test_add_inconsistent_dimension(self):
         """Add two transfer function matrices of different sizes."""
-        sys1 = TransferFunction([[[1., 2.]]], [[[4., 5.]]])
-        sys2 = TransferFunction([[[4., 3.]], [[1., 2.]]],
-                                [[[1., 6.]], [[2., 4.]]])
+        sys1 = TransferFunction(
+            [
+                [[1., 2.]],
+                [[2., -2.]],
+                [[2., 1.]],
+            ],
+            [
+                [[4., 5.]],
+                [[5., 2.]],
+                [[3., 2.]],
+            ],
+        )
+        sys2 = TransferFunction(
+            [
+                [[4., 3.]],
+                [[1., 2.]],
+            ],
+            [
+                [[1., 6.]],
+                [[2., 4.]],
+            ]
+        )
         with pytest.raises(ValueError):
             sys1.__add__(sys2)
         with pytest.raises(ValueError):
diff --git a/control/xferfcn.py b/control/xferfcn.py
@@ -594,6 +594,12 @@ def __add__(self, other):
         if not isinstance(other, TransferFunction):
             return NotImplemented
 
+        # Promote SISO object to compatible dimension
+        if self.issiso() and not other.issiso():
+            self = np.ones((other.noutputs, other.ninputs)) * self
+        elif not self.issiso() and other.issiso():
+            other = np.ones((self.noutputs, self.ninputs)) * other
+
         # Check that the input-output sizes are consistent.
         if self.ninputs != other.ninputs:
             raise ValueError(
