FA-88083 / Inverse kinematics solvers / Member archive

First wrist angle is read from the bottom row instead of the last column · case 03

The first angle equals a function of the last angle, so a and g appear swapped.

Member previewVariant 3 · 3 implementations · 7 checks per implementation

Case contract

Input [R, flip]: R is a 3x3 wrist rotation R = Rz(a) Ry(b) Rz(g). Return [a,b,g] in degrees rounded to 4. With flip false b is in [0,180]; with flip true b is negative and a,g are shifted by 180 degrees. When hypot(R02,R12) < 1e-9 the wrist is singular: a=0 and b=0 (R22>0, g=atan2(R10,R00)) or b=180 (g=atan2(R01,-R00)).

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
negative angles	`[-150.0, 75.0, -150.0]`	`[-120.0, 75.0, -150.0]`	Failed

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