| /* Translated into C++ by SciPy developers in 2024. | |
| * | |
| * This was not part of the original cephes library. | |
| */ | |
| namespace xsf { | |
| namespace cephes { | |
| namespace detail { | |
| constexpr double besselpoly_EPS = 1.0e-17; | |
| } | |
| XSF_HOST_DEVICE inline double besselpoly(double a, double lambda, double nu) { | |
| int m, factor = 0; | |
| double Sm, relerr, Sol; | |
| double sum = 0.0; | |
| /* Special handling for a = 0.0 */ | |
| if (a == 0.0) { | |
| if (nu == 0.0) { | |
| return 1.0 / (lambda + 1); | |
| } else { | |
| return 0.0; | |
| } | |
| } | |
| /* Special handling for negative and integer nu */ | |
| if ((nu < 0) && (std::floor(nu) == nu)) { | |
| nu = -nu; | |
| factor = static_cast<int>(nu) % 2; | |
| } | |
| Sm = std::exp(nu * std::log(a)) / (Gamma(nu + 1) * (lambda + nu + 1)); | |
| m = 0; | |
| do { | |
| sum += Sm; | |
| Sol = Sm; | |
| Sm *= -a * a * (lambda + nu + 1 + 2 * m) / ((nu + m + 1) * (m + 1) * (lambda + nu + 1 + 2 * m + 2)); | |
| m++; | |
| relerr = std::abs((Sm - Sol) / Sm); | |
| } while (relerr > detail::besselpoly_EPS && m < 1000); | |
| if (!factor) | |
| return sum; | |
| else | |
| return -sum; | |
| } | |
| } // namespace cephes | |
| } // namespace xsf | |