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docs: note high-precision requirement for Phase 9c/10 uniformization
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The Java uniformization classes (FundamentalPolygonUtility, CanonicalFormUtility)
rely on the *Big arbitrary-precision geometry (MathContext(50)) because products
of hyperbolic isometry generators grow exponentially and double fails to verify
the group relation ∏gᵢ = Id. Record this planning-relevant prerequisite and
resolve the contradiction in java-parity.md, which previously listed *Big as
permanently out of scope.

- CLAUDE.md: † note on the Phase-9 not-yet-ported table
- java-parity.md: *Big exception (localized high-precision substrate for 9c/10)
- phases.md: precision prerequisite as 9c sub-task + effort estimate
- design-decisions.md: new "Scalar type: double, with one localized exception"

Core flattening (Newton/energy/Eigen solver) stays double; the substrate
(cpp_dec_float_50 / mpreal) is localized to the uniformization module only.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
This commit is contained in:
Tarik Moussa
2026-05-28 07:41:23 +02:00
parent 1ff5382c8b
commit ca936b7652
4 changed files with 42 additions and 4 deletions
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11
doc/roadmap/java-parity.md
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@@ -89,7 +89,16 @@ items were unrecorded and have now been added above:
Everything else unmentioned is intentionally out of scope: the `plugin/*` jReality
Swing GUI, the `MTJ*`/`Tao*`/`*PETSc` solver bindings (replaced by Eigen), the
convergence/`*Series` test harness, and the `*Big` arbitrary-precision geometry
(`P2Big`/`PnBig`/`RnBig` — deliberately dropped in favour of `Simple_cartesian<double>`).
(`P2Big`/`PnBig`/`RnBig` — deliberately dropped from the core in favour of `Simple_cartesian<double>`).
> **Exception — `*Big` is NOT permanently out of scope.** The Phase 9c/10 uniformization
> classes (`FundamentalPolygonUtility`, `CanonicalFormUtility`, rows 55–56 above) build on
> the `*Big` classes in Java for a reason: products of hyperbolic isometry generators grow
> exponentially, so `double` fails when verifying the group relation ∏gᵢ = Id (`MathContext(50)`
> = 50 significant digits in Java). When those classes are ported, a localized high-precision
> substrate (`boost::multiprecision::cpp_dec_float_50` or MPFR `mpreal`) must be reintroduced —
> **only inside the uniformization module**, not in the core flattening or the Eigen solver.
> See the Phase-9 note in `CLAUDE.md`.
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