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Tarik Moussa dd87b8007b
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Phase 9a-Newton: newton_cp_euclidean + newton_inversive_distance
Wires the two Phase-9a functionals into the Newton-solver layer so
they are operational end-to-end.  CGAL test count: 212 → 219 (+7).

Solvers
───────
* newton_cp_euclidean(mesh, x0, m, tol, max_iter)
    - Uses cp_euclidean_hessian — analytic 2×2-per-edge BPS-2010
      formula h_jk = sin θ / (cosh Δρ − cos θ).
    - SparseQR fallback handles the gauge-singular case when no face
      is pinned (caller error, but we recover gracefully).
    - Strictly-convex energy ⇒ quadratic convergence near optimum.

* newton_inversive_distance(mesh, x0, m, tol, max_iter, hess_eps)
    - Uses an inline FD Hessian (n × gradient evaluations per step) —
      mirrors the Phase 4a HyperIdeal solver in spirit.
    - Analytic alternative via Glickenstein 2011 eq. (4.6) is tracked
      in doc/roadmap/research-track.md as Phase 9a.2-analytic.
    - Sensitive to initial point; the test suite always starts from
      a natural-theta setup (u = 0 is the equilibrium when
      compute_inversive_distance_init_from_mesh was called).

Tests (test_newton_phase9a.cpp, 7 cases)
────────────────────────────────────────
* CPEuclidean_NaturalPhi_ClosedTetrahedron_ConvergesInZeroIterations
* CPEuclidean_PerturbedStart_ConvergesBackToEquilibrium
* CPEuclidean_OpenTetrahedron_NaturalPhi_Converges
* InversiveDistance_NaturalTheta_Triangle_ConvergesInZero
* InversiveDistance_PerturbedQuadStrip_Converges
* InversiveDistance_PerturbedTetrahedron_Converges
* CPEuclidean_UsesAnalyticHessian
    Regression guard: 3-DOF problem converges in ≤ 10 iterations even
    with strong perturbation, confirming the analytic Hessian path is
    actually used.

All seven tests pass.  Full CGAL suite: 219/219 PASSED, 0 SKIPPED.

Roadmap additions (`doc/roadmap/phases.md`)
───────────────────────────────────────────
New Phase 11+ section flags two Java sub-packages as optional/deferred
ports, recorded for project memory but not roadmap commitments:

* 11a — Schottky uniformisation (Java plugin/schottky/*, ~3000 LoC)
        Hyperbolic loxodromic group acting on S²; complement of the
        Phase 10c Fuchsian-group representation in H².  Requires
        Phase 10b period matrix + Möbius-group machinery from Phase 7.
        Effort: very large (4-6 weeks).

* 11b — Riemann maps (Java plugin/riemannmap/*, ~1500 LoC)
        Discrete Riemann mapping theorem; texture mapping of bounded
        planar regions, classical conformal mapping for engineering.
        Requires Phase 10b' quasi-isothermic or Phase 9a.1 CP-Euclidean.
        Effort: large (3-4 weeks).

Both are explicitly NOT roadmap commitments — they live in the doc so
they aren't re-discovered.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
2026-05-21 21:10:00 +02:00
..