Finding-C from doc/reviewer/external-audit-2026-05-30.md.
The box comment at the top and the function-level comment above
euclidean_cot_weights() both stated:
cot_k = (t_adj1·l123 − t_adj2·t_opp) / denom2 ← WRONG
The correct formula (verified numerically on a 3-4-5 right triangle,
expected cot1=4/3, cot2=3/4, cot3=0) is:
cot_k = (t_opp · l123 − t_a · t_b) / denom2
where t_opp is the t-value of the edge OPPOSITE vertex k, and t_a/t_b
are the t-values of the two edges ADJACENT to vertex k.
The implementation in euclidean_cot_weights() was already correct;
only the documentation was wrong.
Changes (documentation only, zero code changes):
- Box comment: rewritten with correct formula and explicit per-vertex
assignment (cot1: t_opp=t23, t_a=t12, t_b=t31; etc.)
- Box comment: added missing ½ factor to Hessian contribution lines
- Function-level comment: corrected to (t_opp·l123 − t_a·t_b)/(8·Area)
with a pointer to the box comment for the full assignment
- Inline return comment in euclidean_cot_weights(): now shows the
mapping (cot1: t_opp=t23, t_a=t12, t_b=t31) directly at the formula
263/263 CGAL tests pass, 0 failed.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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