HFCHEBY2D13

A Fortran90 source code of Function HFCHEBY2D13 to calculate values of Ambartsumian-Chandrasekhar H-function for isotropic scattering with 13-digit accuracy for a given set of values for the single scattering albedo and the angular parameter mu. The formula implemented is based on numerical fittings by a bivariate Chebyshev polynomial to the values of this function calculated with 15-digit accuracy.