FA-88243 / Inverse kinematics solvers / Member archive

Trajectory branch distance ignores joint wrap-around · case 03

Near the +/-180 seam the solver picks the far branch or reports a spurious jump.

Member previewVariant 3 · 3 implementations · 7 checks per implementation

Case contract

Input [l1,l2,q0,targets,maxjump]: planar 2R arm with continuous joints following a list of targets from joint state q0 (degrees). For each target compute the elbow +/- solutions; unreachable targets append "hold". Choose the solution with the smallest max wrapped joint change from the previous state; if that change exceeds maxjump append "jump" and keep the state. Otherwise unwrap the solution to lie within 180 of the previous angles, append it (3 decimals) and count a flip whenever the elbow sign differs from the last accepted one. Return [outputs, flips].

Why this case matters

Inverse kinematics code turns task-space goals into joint commands; a wrong branch, sign, limit or update order sends a real arm to the wrong pose.

One recorded failure

Sample boundary fixture

This sample comes from the broken implementation of a controlled reproducer.

Boundary fixture	Actual	Expected	Outcome
down to up flip	`[[[-4.734, -129.42], "hold", [146.738, -126.157]], 0]`	`[[[-4.734, -129.42], "hold", [20.581, -233.843]], 1]`	Failed

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