fixed problem with minreal when reduction leaves only a gain and no zeros;

repagh · repagh · commit f70d9419c1ee · 2013-05-22T07:48:40.000Z
poly([]) would return 1 instead of the expected array([1.])
diff --git a/src/matlab.py b/src/matlab.py
@@ -96,7 +96,7 @@
 from control.ctrlutil import unwrap
 from control.freqplot import nyquist, gangof4
 from control.nichols import nichols
-from control.bdalg import series, parallel, negate, feedback
+from control.bdalg import series, parallel, negate, feedback, append
 from control.pzmap import pzmap
 from control.statefbk import ctrb, obsv, gram, place, lqr
 from control.delay import pade
diff --git a/src/xferfcn.py b/src/xferfcn.py
@@ -661,8 +661,12 @@ def minreal(self, tol=None):
                         newzeros.append(z)
                         
                 # keep result
-                num[i][j] = gain * real(poly(newzeros))
+                if len(newzeros):
+                    num[i][j] = gain * real(poly(newzeros))
+                else:
+                    num[i][j] = array([gain])
                 den[i][j] = real(poly(poles))
+                    
 
         # end result
         return TransferFunction(num, den)
diff --git a/tests/xferfcn_test.py b/tests/xferfcn_test.py
@@ -444,6 +444,19 @@ def testMinreal(self):
         np.testing.assert_array_almost_equal(hm.num[0][0], hr.num[0][0])
         np.testing.assert_array_almost_equal(hm.den[0][0], hr.den[0][0])
 
+    def testMinreal2(self):
+        """This one gave a problem, due to poly([]) giving simply 1 
+        instead of numpy.array([1])"""
+        s = TransferFunction([1, 0], [1])
+        G = 6205/(s*(s**2 + 13*s + 1281))
+        Heq = G.feedback(1)
+        H1 = 1/(s+5)
+        H2a = Heq/H1
+        H2b = H2a.minreal()
+        hr = 6205/(s**2+8*s+1241)
+        np.testing.assert_array_almost_equal(H2b.num[0][0], hr.num[0][0])
+        np.testing.assert_array_almost_equal(H2b.den[0][0], hr.den[0][0])
+
     def testMIMO(self):
         """Test conversion of a single input, two-output state-space
         system against the same TF"""
