diff --git a/control/statefbk.py b/control/statefbk.py
index 3d2ef6d9c..15bba5454 100644
--- a/control/statefbk.py
+++ b/control/statefbk.py
@@ -1119,18 +1119,21 @@ def gram(sys, type):
if type not in ['c', 'o', 'cf', 'of']:
raise ValueError("That type is not supported!")
- # TODO: Check for continuous or discrete, only continuous supported for now
- # if isCont():
- # dico = 'C'
- # elif isDisc():
- # dico = 'D'
- # else:
- dico = 'C'
-
- # TODO: Check system is stable, perhaps a utility in ctrlutil.py
- # or a method of the StateSpace class?
- if np.any(np.linalg.eigvals(sys.A).real >= 0.0):
- raise ValueError("Oops, the system is unstable!")
+ # Check if system is continuous or discrete
+ if sys.isctime():
+ dico = 'C'
+
+ # TODO: Check system is stable, perhaps a utility in ctrlutil.py
+ # or a method of the StateSpace class?
+ if np.any(np.linalg.eigvals(sys.A).real >= 0.0):
+ raise ValueError("Oops, the system is unstable!")
+
+ else:
+ assert sys.isdtime()
+ dico = 'D'
+
+ if np.any(np.abs(sys.poles()) >= 1.):
+ raise ValueError("Oops, the system is unstable!")
if type == 'c' or type == 'o':
# Compute Gramian by the Slycot routine sb03md
diff --git a/control/tests/statefbk_test.py b/control/tests/statefbk_test.py
index cb677b40a..4a0472de7 100644
--- a/control/tests/statefbk_test.py
+++ b/control/tests/statefbk_test.py
@@ -98,6 +98,28 @@ def testGramWc(self):
Wctrue = np.array([[18.5, 24.5], [24.5, 32.5]])
Wc = gram(sys, 'c')
np.testing.assert_array_almost_equal(Wc, Wctrue)
+ sysd = ct.c2d(sys, 0.2)
+ Wctrue = np.array([[3.666767, 4.853625],
+ [4.853625, 6.435233]])
+ Wc = gram(sysd, 'c')
+ np.testing.assert_array_almost_equal(Wc, Wctrue)
+
+ @slycotonly
+ def testGramWc2(self):
+ A = np.array([[1., -2.], [3., -4.]])
+ B = np.array([[5.], [7.]])
+ C = np.array([[6., 8.]])
+ D = np.array([[9.]])
+ sys = ss(A,B,C,D)
+ Wctrue = np.array([[ 7.166667, 9.833333],
+ [ 9.833333, 13.5]])
+ Wc = gram(sys, 'c')
+ np.testing.assert_array_almost_equal(Wc, Wctrue)
+ sysd = ct.c2d(sys, 0.2)
+ Wctrue = np.array([[1.418978, 1.946180],
+ [1.946180, 2.670758]])
+ Wc = gram(sysd, 'c')
+ np.testing.assert_array_almost_equal(Wc, Wctrue)
@slycotonly
def testGramRc(self):
@@ -106,9 +128,15 @@ def testGramRc(self):
C = np.array([[4., 5.], [6., 7.]])
D = np.array([[13., 14.], [15., 16.]])
sys = ss(A, B, C, D)
- Rctrue = np.array([[4.30116263, 5.6961343], [0., 0.23249528]])
+ Rctrue = np.array([[4.30116263, 5.6961343],
+ [0., 0.23249528]])
Rc = gram(sys, 'cf')
np.testing.assert_array_almost_equal(Rc, Rctrue)
+ sysd = ct.c2d(sys, 0.2)
+ Rctrue = np.array([[1.91488054, 2.53468814],
+ [0. , 0.10290372]])
+ Rc = gram(sysd, 'cf')
+ np.testing.assert_array_almost_equal(Rc, Rctrue)
@slycotonly
def testGramWo(self):
@@ -120,6 +148,11 @@ def testGramWo(self):
Wotrue = np.array([[257.5, -94.5], [-94.5, 56.5]])
Wo = gram(sys, 'o')
np.testing.assert_array_almost_equal(Wo, Wotrue)
+ sysd = ct.c2d(sys, 0.2)
+ Wotrue = np.array([[ 1305.369179, -440.046414],
+ [ -440.046414, 333.034844]])
+ Wo = gram(sysd, 'o')
+ np.testing.assert_array_almost_equal(Wo, Wotrue)
@slycotonly
def testGramWo2(self):
@@ -131,6 +164,11 @@ def testGramWo2(self):
Wotrue = np.array([[198., -72.], [-72., 44.]])
Wo = gram(sys, 'o')
np.testing.assert_array_almost_equal(Wo, Wotrue)
+ sysd = ct.c2d(sys, 0.2)
+ Wotrue = np.array([[ 1001.835511, -335.337663],
+ [ -335.337663, 263.355793]])
+ Wo = gram(sysd, 'o')
+ np.testing.assert_array_almost_equal(Wo, Wotrue)
@slycotonly
def testGramRo(self):
@@ -142,15 +180,34 @@ def testGramRo(self):
Rotrue = np.array([[16.04680654, -5.8890222], [0., 4.67112593]])
Ro = gram(sys, 'of')
np.testing.assert_array_almost_equal(Ro, Rotrue)
+ sysd = ct.c2d(sys, 0.2)
+ Rotrue = np.array([[ 36.12989315, -12.17956588],
+ [ 0. , 13.59018097]])
+ Ro = gram(sysd, 'of')
+ np.testing.assert_array_almost_equal(Ro, Rotrue)
def testGramsys(self):
- num =[1.]
- den = [1., 1., 1.]
- sys = tf(num,den)
- with pytest.raises(ValueError):
+ sys = tf([1.], [1., 1., 1.])
+ with pytest.raises(ValueError) as excinfo:
gram(sys, 'o')
- with pytest.raises(ValueError):
+ assert "must be StateSpace" in str(excinfo.value)
+ with pytest.raises(ValueError) as excinfo:
+ gram(sys, 'c')
+ assert "must be StateSpace" in str(excinfo.value)
+ sys = tf([1], [1, -1], 0.5)
+ with pytest.raises(ValueError) as excinfo:
+ gram(sys, 'o')
+ assert "must be StateSpace" in str(excinfo.value)
+ with pytest.raises(ValueError) as excinfo:
+ gram(sys, 'c')
+ assert "must be StateSpace" in str(excinfo.value)
+ sys = ct.ss(sys) # this system is unstable
+ with pytest.raises(ValueError) as excinfo:
+ gram(sys, 'o')
+ assert "is unstable" in str(excinfo.value)
+ with pytest.raises(ValueError) as excinfo:
gram(sys, 'c')
+ assert "is unstable" in str(excinfo.value)
def testAcker(self, fixedseed):
for states in range(1, self.maxStates):
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