fix timebase bug in InterconnectedSystem (issue python-control#754)

murrayrm · murrayrm · commit f17c9194456b · 2022-08-05T21:37:19.000-07:00
diff --git a/control/iosys.py b/control/iosys.py
@@ -871,9 +871,12 @@ def __init__(self, syslist, connections=[], inplist=[], outlist=[],
         if not isinstance(outlist, (list, tuple)):
             outlist = [outlist]
 
-        # Process keyword arguments
+        # Check if dt argument was given; if not, pull from systems
+        dt = kwargs.pop('dt', None)
+
+        # Process keyword arguments (except dt)
         defaults = {'inputs': len(inplist), 'outputs': len(outlist)}
-        name, inputs, outputs, states, dt = _process_namedio_keywords(
+        name, inputs, outputs, states, _ = _process_namedio_keywords(
             kwargs, defaults, end=True)
 
         # Initialize the system list and index
diff --git a/control/tests/timebase_test.py b/control/tests/timebase_test.py
@@ -0,0 +1,37 @@
+import pytest
+import inspect
+import numpy as np
+import control as ct
+
+@pytest.mark.parametrize(
+    "dt1, dt2, dt3", [
+        (0, 0, 0),
+        (0, 0.1, ValueError),
+        (0, None, 0),
+        (0.1, 0, ValueError),
+        (0.1, 0.1, 0.1),
+        (0.1, None, 0.1),
+        (None, 0, 0),
+        (None, 0.1, 0.1),
+        (None, None, None),
+        (0.2, None, 0.2),
+        (0.2, 0.1, ValueError),
+     ])
+@pytest.mark.parametrize("op", [ct.series, ct.parallel, ct.feedback])
+@pytest.mark.parametrize("type", [ct.StateSpace, ct.ss, ct.tf])
+def test_composition(dt1, dt2, dt3, op, type):
+    # Define the system
+    A, B, C, D = [[1, 1], [0, 1]], [[0], [1]], [[1, 0]], 0
+    sys1 = ct.StateSpace(A, B, C, D, dt1)
+    sys2 = ct.StateSpace(A, B, C, D, dt2)
+
+    # Convert to the desired form
+    sys1 = type(sys1)
+    sys2 = type(sys2)
+
+    if inspect.isclass(dt3) and issubclass(dt3, Exception):
+        with pytest.raises(dt3, match="incompatible timebases"):
+            sys3 = op(sys1, sys2)
+    else:
+        sys3 = op(sys1, sys2)
+        assert sys3.dt == dt3
