Merge pull request scipy#2791 from andbo/master

BUG: signal: Bode plot should return continuous phase

scipy/signal/ltisys.py

@@ -983,7 +983,7 @@ def bode(system, w=None, n=100):
     w, y = freqresp(system, w=w, n=n)
 
     mag = 20.0 * numpy.log10(abs(y))
-    phase = numpy.arctan2(y.imag, y.real) * 180.0 / numpy.pi
+    phase = numpy.unwrap(numpy.arctan2(y.imag, y.real)) * 180.0 / numpy.pi
 
     return w, mag, phase
 

scipy/signal/tests/test_ltisys.py

@@ -351,6 +351,12 @@ def test_07(self):
         system = lti([1], [1, 0, 100])
         w, mag, phase = bode(system, n=2)
 
+    def test_08(self):
+        """Test that bode() return continuous phase, issues/2331."""
+        system = lti([], [-10, -30, -40, -60, -70], 1)
+        w, mag, phase = system.bode(w=np.logspace(-3, 40, 100))
+        assert_almost_equal(min(phase), -450, decimal=15)
+
     def test_from_state_space(self):
         # Ensure that bode works with a system that was created from the
         # state space representation matrices A, B, C, D.  In this case,