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Fix scalar feedback for square MIMO state-space systems #1232

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Fix scalar feedback for square MIMO state-space systems #1232

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2 changes: 2 additions & 0 deletions control/statesp.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1003,6 +1003,8 @@ def feedback(self, other=1, sign=-1):
"""
# Convert the system to state space, if possible
try:
if np.isscalar(other) and self.ninputs == self.noutputs:
other = other * eye(self.ninputs)
other = _convert_to_statespace(other)
except:
pass
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25 changes: 25 additions & 0 deletions control/tests/bdalg_test.py
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Original file line number Diff line number Diff line change
Expand Up @@ -143,6 +143,31 @@ def testSSSS2(self, tsys):
0.142857142857143, -0.571428571428571, 0.857142857142857]])
np.testing.assert_array_almost_equal(ans2.D, [[-0.285714285714286]])

def test_mimo_ss_scalar_feedback(self):
"""MIMO state space system with scalar feedback block."""
sys_static = StateSpace([], [], [], [[1, 0], [0, 2]])
ans1 = feedback(sys_static)
ans2 = feedback(sys_static, np.eye(2))
np.testing.assert_array_almost_equal(ans1.D, ans2.D)

ans3 = feedback(sys_static, 2)
ans4 = feedback(sys_static, 2 * np.eye(2))
np.testing.assert_array_almost_equal(ans3.D, ans4.D)

sys_dynamic = StateSpace(
[[-1, 0], [0, -2]], [[1, 0], [0, 1]],
[[1, 0], [0, 1]], [[0, 0], [0, 0]])
ans5 = feedback(sys_dynamic)
ans6 = feedback(sys_dynamic, np.eye(2))
np.testing.assert_array_almost_equal(ans5.A, ans6.A)
np.testing.assert_array_almost_equal(ans5.B, ans6.B)
np.testing.assert_array_almost_equal(ans5.C, ans6.C)
np.testing.assert_array_almost_equal(ans5.D, ans6.D)

sys_nonsquare = StateSpace([], [], [], [[1, 2, 3], [4, 5, 6]])
with pytest.raises(ValueError, match="compatible inputs/outputs"):
feedback(sys_nonsquare)


def testSSTF(self, tsys):
"""State space system with transfer function feedback block."""
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