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perf: compute Twist3.Ad() directly instead of via a throwaway SE3 by petercorke · Pull Request #211 · rai-opensource/spatialmath-python · GitHub

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perf: compute Twist3.Ad() directly instead of via a throwaway SE3 #211

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perf: compute Twist3.Ad() directly instead of via a throwaway SE3 #211

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7 changes: 4 additions & 3 deletions spatialmath/twist.py
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Original file line number Diff line number Diff line change
Expand Up @@ -887,12 +887,13 @@ def Ad(self):
>>> S = Twist3.Rx(0.3)
>>> S.Ad()

.. note:: This method computes the equivalent SE(3) matrix, then the adjoint
of that.
.. note:: Equivalent to, but faster than, ``self.SE3().Ad()`` -- computes
the adjoint directly from the twist's exponential without
constructing an intermediate ``SE3`` instance.

:seealso: :func:`Twist3.ad`, :func:`Twist3.SE3`, :func:`Twist3.exp`
"""
return self.SE3().Ad()
return smb.tr2adjoint(smb.trexp(self.S, check=False))

def skewa(self):
"""
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26 changes: 26 additions & 0 deletions tests/test_twist.py
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Expand Up @@ -179,6 +179,32 @@ def test_exp(self):
tw = Twist3.UnitRevolute([0, 0, 1], [0, 0, 0])
array_compare(tw.exp(pi / 2), SE3.Rz(pi / 2))

def test_Ad(self):
# pure rotation: Ad is block-diagonal [[R,0],[0,R]], no translation
# coupling -- hand-verified ground truth, not derived from Ad() itself.
R = SE3.Rx(0.4).R
S = Twist3(SE3.Rx(0.4))
expected = np.zeros((6, 6))
expected[:3, :3] = R
expected[3:, 3:] = R
nt.assert_almost_equal(S.Ad(), expected)

# pure translation: Ad couples translation into the top-right block
# via skew(t), identity rotation blocks -- also hand-verified.
t = np.r_[1, 2, 3]
S = Twist3(SE3(t))
expected = np.eye(6)
expected[:3, 3:] = skew(t)
nt.assert_almost_equal(S.Ad(), expected)

# general case: cross-check against SE3.Ad(), computed from the same
# twist's own exponential, for several random transforms.
for _ in range(20):
T = SE3.Rand()
S = Twist3(T)
nt.assert_almost_equal(S.Ad(), S.SE3().Ad())
nt.assert_almost_equal(S.Ad(), T.Ad())

def test_arith(self):
# check overloaded *

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