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Merged
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Mar 21, 2020
Merged

handle non proper tf in _common_den() #370

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16498d1
handle non proper tf in _common_den()
bnavigator Jan 28, 2020
a0986c5
rename to allow_nonproper
bnavigator Mar 18, 2020
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28 changes: 28 additions & 0 deletions control/tests/xferfcn_test.py
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Original file line number Diff line number Diff line change
Expand Up @@ -546,6 +546,26 @@ def test_common_den(self):
np.zeros((3, 5, 6)))
np.testing.assert_array_almost_equal(den, denref)

def test_common_den_nonproper(self):
""" Test _common_den with order(num)>order(den) """

tf1 = TransferFunction(
[[[1., 2., 3.]], [[1., 2.]]],
[[[1., -2.]], [[1., -3.]]])
tf2 = TransferFunction(
[[[1., 2.]], [[1., 2., 3.]]],
[[[1., -2.]], [[1., -3.]]])

common_den_ref = np.array([[1., -5., 6.]])

np.testing.assert_raises(ValueError, tf1._common_den)
np.testing.assert_raises(ValueError, tf2._common_den)

_, den1, _ = tf1._common_den(allow_nonproper=True)
np.testing.assert_array_almost_equal(den1, common_den_ref)
_, den2, _ = tf2._common_den(allow_nonproper=True)
np.testing.assert_array_almost_equal(den2, common_den_ref)

@unittest.skipIf(not slycot_check(), "slycot not installed")
def test_pole_mimo(self):
"""Test for correct MIMO poles."""
Expand All @@ -557,6 +577,14 @@ def test_pole_mimo(self):

np.testing.assert_array_almost_equal(p, [-2., -2., -7., -3., -2.])

# non proper transfer function
sys2 = TransferFunction(
[[[1., 2., 3., 4.], [1.]], [[1.], [1.]]],
[[[1., 2.], [1., 3.]], [[1., 4., 4.], [1., 9., 14.]]])
p2 = sys2.pole()

np.testing.assert_array_almost_equal(p2, [-2., -2., -7., -3., -2.])

def test_double_cancelling_poles_siso(self):

H = TransferFunction([1, 1], [1, 2, 1])
Expand Down
28 changes: 26 additions & 2 deletions control/xferfcn.py
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Expand Up @@ -679,7 +679,7 @@ def freqresp(self, omega):

def pole(self):
"""Compute the poles of a transfer function."""
num, den, denorder = self._common_den()
_, den, denorder = self._common_den(allow_nonproper=True)
rts = []
for d, o in zip(den, denorder):
rts.extend(roots(d[:o + 1]))
Expand Down Expand Up @@ -797,7 +797,7 @@ def returnScipySignalLTI(self):

return out

def _common_den(self, imag_tol=None):
def _common_den(self, imag_tol=None, allow_nonproper=False):
"""
Compute MIMO common denominators; return them and adjusted numerators.

Expand All @@ -813,6 +813,9 @@ def _common_den(self, imag_tol=None):
Threshold for the imaginary part of a root to use in detecting
complex poles

allow_nonproper : boolean
Do not enforce proper transfer functions

Returns
-------
num: array
Expand All @@ -822,6 +825,8 @@ def _common_den(self, imag_tol=None):
gives the numerator coefficient array for the ith output and jth
input; padded for use in td04ad ('C' option); matches the
denorder order; highest coefficient starts on the left.
If allow_nonproper=True and the order of a numerator exceeds the
order of the common denominator, num will be returned as None

den: array
sys.inputs by kd
Expand Down Expand Up @@ -906,6 +911,8 @@ def _common_den(self, imag_tol=None):
dtype=float)
denorder = zeros((self.inputs,), dtype=int)

havenonproper = False

for j in range(self.inputs):
if not len(poles[j]):
# no poles matching this input; only one or more gains
Expand All @@ -930,11 +937,28 @@ def _common_den(self, imag_tol=None):
nwzeros.append(poles[j][ip])

numpoly = poleset[i][j][2] * np.atleast_1d(poly(nwzeros))

# td04ad expects a proper transfer function. If the
# numerater has a higher order than the denominator, the
# padding will fail
if len(numpoly) > maxindex + 1:
if allow_nonproper:
havenonproper = True
break
raise ValueError(
self.__str__() +
"is not a proper transfer function. "
"The degree of the numerators must not exceed "
"the degree of the denominators.")

# numerator polynomial should be padded on left and right
# ending at maxindex to line up with what td04ad expects.
num[i, j, maxindex+1-len(numpoly):maxindex+1] = numpoly
# print(num[i, j])

if havenonproper:
num = None

return num, den, denorder

def sample(self, Ts, method='zoh', alpha=None):
Expand Down