Fix minreal() non-deterministic behavior from uninitialized memory

jamestjsp · claude · jamestjsp · commit 674f2e828538 · 2026-02-02T07:20:57.000-06:00
- Change empty() to zeros() for padded B/C matrices in minreal()
- Fix pytest fixture syntax in minreal_test.py
- Restore original assertion: nreductions == 2

The bug caused garbage memory values in extra columns when
ninputs != noutputs, leading to non-deterministic tb01pd results.

Co-Authored-By: Claude Opus 4.5 &lt;noreply@anthropic.com&gt;
diff --git a/control/statesp.py b/control/statesp.py
@@ -1176,9 +1176,9 @@ def minreal(self, tol=0.0):
         if self.nstates:
             try:
                 from .slicot_compat import tb01pd
-                B = empty((self.nstates, max(self.ninputs, self.noutputs)))
+                B = zeros((self.nstates, max(self.ninputs, self.noutputs)))
                 B[:, :self.ninputs] = self.B
-                C = empty((max(self.noutputs, self.ninputs), self.nstates))
+                C = zeros((max(self.noutputs, self.ninputs), self.nstates))
                 C[:self.noutputs, :] = self.C
                 A, B, C, nr = tb01pd(self.nstates, self.ninputs, self.noutputs,
                                      self.A, B, C, tol=tol)
diff --git a/control/tests/minreal_test.py b/control/tests/minreal_test.py
@@ -13,8 +13,8 @@
 from itertools import permutations
 
 
-@pytest.fixture
-def fixedseed(scope="class"):
+@pytest.fixture(scope="class")
+def fixedseed():
     np.random.seed(5)
 
 
@@ -79,9 +79,8 @@ def testMinrealBrute(self):
                             # Find the closest zero
                             assert min(abs(z1 - z)) <= 1e-7
 
-        # Make sure some reductions occurred (exact count depends on minreal impl)
-        # (May vary between slycot and slicot implementations)
-        assert nreductions >= 0
+        # Verify expected reductions occur (seed=5 yields 2 reducible systems)
+        assert nreductions == 2
 
     def testMinrealSS(self):
         """Test a minreal model reduction"""
