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[Intention]: OrthogonalL2Bases — weight↔measure isometry enhancement #46

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@mrdouglasny

Roadmap area: OrthogonalL2Bases

Items in scope

What & why. One orthogonal family gives two bases depending on where the weight sits: the bare polynomials Hₙ/√(n!) as an ONB of the weighted / probability (e.g. N(0,1) — expansions, moment problems, chaos), or the Hₙ·√w functions as an ONB of Lebesgue L²(dx) (e.g. Hermite functions / QHO states, PDE, signal processing). They are the same object times √w, and √w is an isometry L²(w·μ) ≅ L²(μ). The roadmap builds only the Lebesgue side; this adds the isometry (plus a missing one-line HilbertBasis transport) so both sides come from one construction — neither normalization privileged, no per-consumer re-derivation.

Targets (narrow):

  • Part 0: weightL2Isometry, HilbertBasis.mapₗᵢ (+ mapₗᵢ_apply).
  • A1: derivative_hermite_succ, integrable_aeval_mul_gaussian, hermite_generating_function, orthogonality (integral_hermite_mul_hermite_mul_gaussian Lebesgue + integral_hermite_mul_hermite_gaussianReal measure).
  • B2: barePolyLp, orthonormal_barePolyLp, barePolyLp_ortho_eq_bot, hilbertBasisOfWeightedMeasure, hilbertBasisOfOrthogonalSystem (+ coe_*).
  • A3′: gaussianHermiteHilbertBasis (+ coe_*), memLp_hermite_gaussianReal.

Not claiming (open): B1 completeness, the Hermite-function object API (A2), B3 product/pi, Chebyshev (C).

Notes

A1 is implemented in TauCetiProject/TauCeti#499 (draft). Roadmap README + Targets.lean change is #45.

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