Function lupnt::InitLtMinusTtFit

Function Documentation

void lupnt::InitLtMinusTtFit(Real t_start_tdb, Real t_end_tdb, double segment_length, int num_coeffs)

Fit TL−TT(TDB) over a time window using piecewise Chebyshev polynomials.

Performs a single forward sweep from the reference epoch T₀+TDB₀ to t_end_tdb, evaluating the Turyshev 2026 Eq. 57 integrand at every Chebyshev-Gauss node (processed in temporal order) and building the DCT Chebyshev fit segment-by-segment. This avoids repeating the long T₀→t_start integral for each node independently.

After this call, TdbToLtMinusTt() will use the fit for epochs in [t_start_tdb, t_end_tdb]; epochs outside that window fall back to direct integration.

Fit TL−TT(TDB) over [t_start_tdb, t_end_tdb] with piecewise Chebyshev polynomials. After this call TdbToLtMinusTt() is fast inside the window.

Parameters:

  • t_start_tdb – Start of fitting window [s from J2000, TDB]

  • t_end_tdb – End of fitting window [s from J2000, TDB]

  • segment_length – Segment length [s] (default 1 day)

  • num_coeffs – Chebyshev degree+1 per segment (default 13)