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Fix find_eqpt when y0 is None #798

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Merged
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Nov 26, 2022
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Fix find_eqpt when y0 is None #798

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11 changes: 8 additions & 3 deletions control/iosys.py
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Original file line number Diff line number Diff line change
Expand Up @@ -2138,10 +2138,15 @@ def rootfun(z):
dx = sys._rhs(t, x, u) - dx0
if dtime:
dx -= x # TODO: check
dy = sys._out(t, x, u) - y0

# Map the results into the constrained variables
return np.concatenate((dx[deriv_vars], dy[output_vars]), axis=0)
# If no y0 is given, don't evaluate the output function
if y0 is None:
return dx[deriv_vars]
else:
dy = sys._out(t, x, u) - y0

# Map the results into the constrained variables
return np.concatenate((dx[deriv_vars], dy[output_vars]), axis=0)

# Set the initial condition for the root finding algorithm
z0 = np.concatenate((x[state_vars], u[input_vars]), axis=0)
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11 changes: 11 additions & 0 deletions control/tests/iosys_test.py
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Original file line number Diff line number Diff line change
Expand Up @@ -822,6 +822,17 @@ def test_find_eqpts(self, tsys):
np.testing.assert_array_almost_equal(
nlsys_full._rhs(0, xeq, ueq)[-4:], np.zeros((4,)), decimal=5)

# The same test as previous, but now all constraints are in the state vector
nlsys_full = ios.NonlinearIOSystem(pvtol_full, None)
xeq, ueq, result = ios.find_eqpt(
nlsys_full, [0, 0, 0.1, 0.1, 0, 0], [0.01, 4*9.8],
idx=[2, 3, 4, 5], ix=[0, 1, 2, 3], return_result=True)
assert result.success
np.testing.assert_array_almost_equal(
nlsys_full._out(0, xeq, ueq)[[2, 3]], [0.1, 0.1], decimal=5)
np.testing.assert_array_almost_equal(
nlsys_full._rhs(0, xeq, ueq)[-4:], np.zeros((4,)), decimal=5)

# Fix one input and vary the other
nlsys_full = ios.NonlinearIOSystem(pvtol_full, None)
xeq, ueq, result = ios.find_eqpt(
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