HKAPPROXEFIN.F90

Description

This Fortran 90 source program computes the Neumann-series expansion coefficients H_k(mu) (k = 1, 2, ..., 94) of the Ambartsumian–Chandrasekhar H-function H(a, mu) for isotropic scattering, using the new recurrence relation developed by Kiyoshi Kawabata (2026, JQSRT). Here, mu denotes the usual angular variable, and a is the single-scattering albedo. Values of H(a, mu) for arbitrary pairs (a, mu) are obtained by summing the Neumann series Σ_{k=0}^{94} H_k(mu) a^k together with a correction factor applied for a > 0.7504. Timing and numerical-accuracy tests for a fast mode and a regular mode of computing H(a, mu) on a 248×248 grid in (a, mu) are performed, and the results are printed for comparison with those produced by the Fortran 90 routine HFISCA (2022, Astrophysics and Space Science, 367:102). The fast mode executes roughly ten times faster than HFISCA, whereas the regular mode is slower than HFISCA by a factor of about three. The numerical values of H(a, mu) are accurate to at least 12 significant digits.

Institutions

• Tokyo University of Science

  Tokyo, Tokyo

Categories

Licence