
ID	0439
Class	DOCUMENTATION
Severity	1
Status	blocked

Models: RbCable/RBCable, RbCable/6DofCable, RbCable/Ring

Found: 2026-11-03

Decision needed: the model author (or the owner) says what Alpha, Beta and Epsilon (AlphaN ... EpsilonT in Ring) mean, their unit and sane values. Needs the model author.

Evidence

src/RMCable/RBCable.cpp:20-22 and src/RMCable/Cable6Dof.cpp:27-29 read Alpha, Beta, Epsilon with no default; src/RMCable/Ring.cpp:24-32 reads the nine Alpha/Beta/Epsilon + N/M/T values the same way. In RBCable.cpp:242-245 the constraint right-hand side is 2 * m_alpha * CDot + m_beta * m_beta * C and m_epsilon is added to the diagonal of W W^T. The headers' option tables said only "...". Since 3.1.4 they say "constraint-solver gain (required); the author did not document its meaning". Example files use Alpha=0.9, Beta=0.9, Epsilon=1e-6 (examples/input/RigidBodyCable.xml) and 1.0, 1.0, 0.0001 (header examples).

Effect

A user cannot tell what the three gains do, which values are sane, or how they trade accuracy against stiffness.

Possible fix

Ask the author; write meaning, unit and a range into the three headers. No code change.

Test that would prove it

None; a docs check that no @addoption description is ....

Risk

None; documentation only.