@@ -23,3 +23,4 @@ Untitled*.ipynb
 # Files created by or for emacs (RMM, 29 Dec 2017)
 *~
 TAGS
+result_images/
@@ -0,0 +1 @@
+/Users/murray/Dropbox/macosx/src/python-control/murrayrm/control/tests/baseline_images/freqresp_test/gangof4-pvtol.png
@@ -18,6 +18,8 @@
 from control.matlab import ss, tf, bode, rss
 from control.tests.conftest import slycotonly
 
+from matplotlib.testing.decorators import image_comparison
+
 pytestmark = pytest.mark.usefixtures("mplcleanup")
 
 
@@ -345,3 +347,25 @@ def test_phase_wrap(TF, wrap_phase, min_phase, max_phase):
     mag, phase, omega = ctrl.bode(TF, wrap_phase=wrap_phase)
     assert(min(phase) >= min_phase)
     assert(max(phase) <= max_phase)
+
+@pytest.fixture
+def pvtol_inner():
+    m = 4               # mass of aircraft
+    J = 0.0475          # inertia around pitch axis
+    r = 0.25            # distance to center of force
+    g = 9.8             # gravitational constant
+    c = 0.05            # damping factor (estimated)
+    
+    # Transfer functions for dynamics
+    Pi = ctrl.tf([r], [J, 0, 0])        # inner loop (roll)
+
+    k, a, b = 200, 2, 50                # control parameters
+    Ci = k * ctrl.tf([1, a], [1, b])    # lead compensator
+
+    return (Pi, Ci)
+
+# Regression test for Gang of 4 plots
+@image_comparison(baseline_images=['gangof4-pvtol'], extensions=['png'])
+def test_gangof4_pvtol(pvtol_inner):
+    plt.figure(num=None, figsize=(8, 6), dpi=80)
+    ctrl.gangof4(*pvtol_inner)
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