Merge pull request #447 from sawyerbfuller/fix-dt-impulse-size

fix impulse size for discrete-time impulse response

control/tests/timeresp_test.py

@@ -218,6 +218,15 @@ def test_impulse_response(self):
         np.testing.assert_array_almost_equal(
             yy, np.vstack((youttrue, np.zeros_like(youttrue))), decimal=4)
 
+    def test_discrete_time_impulse(self):
+        # discrete time impulse sampled version should match cont time
+        dt = 0.1
+        t = np.arange(0, 3, dt)
+        sys = self.siso_tf1
+        sysdt = sys.sample(dt, 'impulse')
+        np.testing.assert_array_almost_equal(impulse_response(sys, t)[1],
+                                             impulse_response(sysdt, t)[1])
+
     def test_initial_response(self):
         # Test SISO system
         sys = self.siso_ss1

control/timeresp.py

@@ -822,7 +822,7 @@ def impulse_response(sys, T=None, X0=0., input=0, output=None, T_num=None,
         new_X0 = B + X0
     else:
         new_X0 = X0
-        U[0] = 1.
+        U[0] = 1./sys.dt # unit area impulse
 
     T, yout, _xout = forced_response(sys, T, U, new_X0, transpose=transpose,
                                      squeeze=squeeze)