Rudimentary test for stability_margin with discrete TF

bnavigator · bnavigator · commit 1a27e627ebfe · 2020-11-16T22:32:44.000+01:00
diff --git a/control/tests/margin_test.py b/control/tests/margin_test.py
@@ -3,7 +3,8 @@
 margin_test.py - test suite for stability margin commands
 
 RMM, 15 Jul 2011
-BG, 30 June 2020 -- convert to pytest, gh-425
+BG, 30 Jun 2020 -- convert to pytest, gh-425
+BG, 16 Nov 2020 -- pick from gh-438 and add discrete test
 """
 from __future__ import print_function
 
@@ -134,7 +135,6 @@ def test_phase_crossover_frequencies():
         omega, gain = phase_crossover_frequencies(tf)
 
 
-
 def test_mag_phase_omega():
     """Test for bug reported in gh-58"""
     sys = TransferFunction(15, [1, 6, 11, 6])
@@ -327,3 +327,14 @@ def test_zmore_stability_margins(tsys_zmore):
                        tsys_zmore['result'],
                        atol=tsys_zmore['atol'],
                        rtol=tsys_zmore['rtol'])
+
+
+@pytest.mark.parametrize(
+    'cnum, cden, dt, ref',
+    [([2], [1, 3, 2, 0], 1e-2,  # gh-465
+      (2.9558, 32.8170, 0.43584, 1.4037, 0.74953, 0.97079))])
+def test_stability_margins_discrete(cnum, cden, dt, ref):
+    """Test stability_margins with discrete TF input"""
+    tf = TransferFunction(cnum, cden).sample(dt)
+    out = stability_margins(tf)
+    assert_allclose(out, ref, atol=1.5e-2)
