Added singularity check to the residualization method

mp4096 · mp4096 · commit bf6c446f0e5b · 2016-07-13T19:43:07.000+02:00
* Changed the unit test in matlab_test.py so that no error is thrown
diff --git a/control/modelsimp.py b/control/modelsimp.py
@@ -181,8 +181,8 @@ def modred(sys, ELIM, method='matchdc'):
         # if matchdc, residualize
 
         # Check if the matrix A22 is invertible
-        # if np.linalg.matrix_rank(A22) != len(ELIM):
-        #     raise ValueError("Matrix A22 is singular to working precision.")
+        if np.linalg.matrix_rank(A22) != len(ELIM):
+            raise ValueError("Matrix A22 is singular to working precision.")
 
         # Now precompute A22\A21 and A22\B2 (A22I = inv(A22))
         # We can solve two linear systems in one pass, since the
diff --git a/control/tests/matlab_test.py b/control/tests/matlab_test.py
@@ -363,7 +363,7 @@ def testBalred(self):
 
     def testModred(self):
         modred(self.siso_ss1, [1])
-        modred(self.siso_ss2 * self.siso_ss3, [1, 2])
+        modred(self.siso_ss2 * self.siso_ss3, [0, 1])
         modred(self.siso_ss3, [1], 'matchdc')
         modred(self.siso_ss3, [1], 'truncate')
 
