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fix issue #240: _common_den was not padding properly #242

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Merged
murrayrm merged 1 commit into from
Dec 22, 2018
Merged

fix issue #240: _common_den was not padding properly #242

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23 changes: 23 additions & 0 deletions control/tests/convert_test.py
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Original file line number Diff line number Diff line change
Expand Up @@ -245,6 +245,29 @@ def testTf2SsDuplicatePoles(self):
except ImportError:
print("Slycot not present, skipping")

@unittest.skipIf(not slycot_check(), "slycot not installed")
def test_tf2ss_robustness(self):
"""Unit test to make sure that tf2ss is working correctly.
Source: https://github.com/python-control/python-control/issues/240
"""
import control

num = [ [[0], [1]], [[1], [0]] ]
den1 = [ [[1], [1,1]], [[1,4], [1]] ]
sys1tf = control.tf(num, den1)
sys1ss = control.tf2ss(sys1tf)

# slight perturbation
den2 = [ [[1], [1e-10, 1, 1]], [[1,4], [1]] ]
sys2tf = control.tf(num, den2)
sys2ss = control.tf2ss(sys2tf)

# Make sure that the poles match for StateSpace and TransferFunction
np.testing.assert_array_almost_equal(np.sort(sys1tf.pole()),
np.sort(sys1ss.pole()))
np.testing.assert_array_almost_equal(np.sort(sys2tf.pole()),
np.sort(sys2ss.pole()))

def suite():
return unittest.TestLoader().loadTestsFromTestCase(TestConvert)

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18 changes: 18 additions & 0 deletions control/tests/timeresp_test.py
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Expand Up @@ -15,6 +15,7 @@
from control.statesp import *
from control.xferfcn import TransferFunction, _convertToTransferFunction
from control.dtime import c2d
from control.exception import slycot_check

class TestTimeresp(unittest.TestCase):
def setUp(self):
Expand Down Expand Up @@ -233,6 +234,23 @@ def test_discrete_initial(self):
t, yout = impulse_response(h1, np.arange(4))
np.testing.assert_array_equal(yout[0], [0., 1., 0., 0.])

@unittest.skipIf(not slycot_check(), "slycot not installed")
def test_step_robustness(self):
"Unit test: https://github.com/python-control/python-control/issues/240"
# Create 2 input, 2 output system
num = [ [[0], [1]], [[1], [0]] ]

den1 = [ [[1], [1,1]], [[1,4], [1]] ]
sys1 = TransferFunction(num, den1)

den2 = [ [[1], [1e-10, 1, 1]], [[1,4], [1]] ] # slight perturbation
sys2 = TransferFunction(num, den2)

# Compute step response from input 1 to output 1, 2
t1, y1 = step_response(sys1, input=0)
t2, y2 = step_response(sys2, input=0)
np.testing.assert_array_almost_equal(y1, y2)

def suite():
return unittest.TestLoader().loadTestsFromTestCase(TestTimeresp)

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19 changes: 12 additions & 7 deletions control/xferfcn.py
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Expand Up @@ -800,9 +800,13 @@ def _common_den(self, imag_tol=None):
num[i,j,0] = poleset[i][j][2]
else:
# create the denominator matching this input
# polyfromroots gives coeffs in opposite order from what we use
# coefficients should be padded on right, ending at np
np = len(poles[j])
den[j,np::-1] = polyfromroots(poles[j]).real
denorder[j] = np

# now create the numerator, also padded on the right
for i in range(self.outputs):
# start with the current set of zeros for this output
nwzeros = list(poleset[i][j][0])
Expand All @@ -811,14 +815,15 @@ def _common_den(self, imag_tol=None):
for ip in chain(poleset[i][j][3],
range(poleset[i][j][4],np)):
nwzeros.append(poles[j][ip])

numpoly = poleset[i][j][2] * polyfromroots(nwzeros).real
m = npmax - len(numpoly)
#print(j,i,m,len(numpoly),len(poles[j]))
if m < 0:
num[i,j,::-1] = numpoly
else:
num[i,j,:m:-1] = numpoly
# print(numpoly, den[j])
# polyfromroots gives coeffs in opposite order => invert
# numerator polynomial should be padded on left and right
# ending at np to line up with what td04ad expects...
num[i, j, np+1-len(numpoly):np+1] = numpoly[::-1]
# print(num[i, j])

if (abs(den.imag) > epsnm).any():
print("Warning: The denominator has a nontrivial imaginary part: %f"
% abs(den.imag).max())
Expand Down