impoed unit tests

sawyerbfuller · sawyerbfuller · commit 94fe55e73cc1 · 2021-03-12T13:22:30.000-08:00
diff --git a/control/margins.py b/control/margins.py
@@ -300,6 +300,7 @@ def stability_margins(sysdata, returnall=False, epsw=0.0, method='best'):
     determined by the frequency of maximum sensitivity (given by the
     magnitude of 1/(1+L)).
     """
+    # TODO: FRD method for cont-time systems doesn't work
     try:
         if isinstance(sysdata, frdata.FRD):
             sys = frdata.FRD(sysdata, smooth=True)
@@ -408,7 +409,6 @@ def _dstab(w):
         w_180 = np.array(
             [sp.optimize.brentq(_arg, sys.omega[i], sys.omega[i+1])
              for i in widx])
-        # TODO: replace by evalfr(sys, 1J*w) or sys(1J*w), (needs gh-449)
         w180_resp = sys(1j * w_180)
 
         # Find all crossings, note that this depends on omega having
diff --git a/control/tests/margin_test.py b/control/tests/margin_test.py
@@ -356,10 +356,24 @@ def test_stability_margins_discrete(cnum, cden, dt, ref, rtol):
     out = stability_margins(tf, method='poly')
     assert_allclose(out, ref, rtol=rtol)
 
+
 def test_stability_margins_methods():
-    sys = TransferFunction(1, (1, 2))
+    # the following system gives slightly inaccurate result for DT systems
+    # because of numerical issues
+    omegan = 1
+    zeta = 0.5
+    resonance = TransferFunction(omegan**2, [1, 2*zeta*omegan, omegan**2])
+    omegan2 = 100
+    resonance2 = TransferFunction(omegan2**2, [1, 2*zeta*omegan2, omegan2**2])
+    sys = 5 * resonance * resonance2
+    sysd = sys.sample(0.001, 'zoh')
     """Test stability_margins() function with different methods"""
-    out = stability_margins(sys, method='best')
-    out = stability_margins(sys, method='frd')
-    out = stability_margins(sys, method='poly')
-
+    out = stability_margins(sysd, method='best')
+    assert_allclose(
+        (18.876634845228644, 11.244969911924102, 0.40684128014454546,
+         9.763585543509473, 4.351735617240803, 2.559873290031937),
+        stability_margins(sysd, method='poly'))
+    assert_allclose(
+        (18.876634740386308, 26.356358386241055, 0.40684127995261044,
+         9.763585494645046, 2.3293357226374805, 2.55985695034263),
+        stability_margins(sysd, method='frd'))
