void acb_hurwitz_zeta(acb_t z, const acb_t s, const acb_t a, slong prec) { if (acb_is_one(a) && acb_is_int(s) && arf_cmpabs_2exp_si(arb_midref(acb_realref(s)), FLINT_BITS - 1) < 0) { acb_zeta_si(z, arf_get_si(arb_midref(acb_realref(s)), ARF_RND_DOWN), prec); return; } _acb_poly_zeta_cpx_series(z, s, a, 0, 1, prec); }
/* todo: use euler product for complex s, and check efficiency for large negative integers */ void acb_dirichlet_zeta(acb_t res, const acb_t s, slong prec) { acb_t a; double cutoff; if (acb_is_int(s) && arf_cmpabs_2exp_si(arb_midref(acb_realref(s)), FLINT_BITS - 1) < 0) { acb_zeta_si(res, arf_get_si(arb_midref(acb_realref(s)), ARF_RND_DOWN), prec); return; } cutoff = 24.0 * prec * sqrt(prec); if (arf_cmpabs_d(arb_midref(acb_imagref(s)), cutoff) >= 0 && arf_cmpabs_d(arb_midref(acb_realref(s)), 10 + prec * 0.1) <= 0) { acb_dirichlet_zeta_rs(res, s, 0, prec); return; } acb_init(a); acb_one(a); if (arf_sgn(arb_midref(acb_realref(s))) < 0) { acb_t t, u, v; slong wp = prec + 6; acb_init(t); acb_init(u); acb_init(v); acb_sub_ui(t, s, 1, wp); /* 2 * (2pi)^(s-1) */ arb_const_pi(acb_realref(u), wp); acb_mul_2exp_si(u, u, 1); acb_pow(u, u, t, wp); acb_mul_2exp_si(u, u, 1); /* sin(pi*s/2) */ acb_mul_2exp_si(v, s, -1); acb_sin_pi(v, v, wp); acb_mul(u, u, v, wp); /* gamma(1-s) zeta(1-s) */ acb_neg(t, t); acb_gamma(v, t, wp); acb_mul(u, u, v, wp); acb_hurwitz_zeta(v, t, a, wp); acb_mul(res, u, v, prec); acb_clear(t); acb_clear(u); acb_clear(v); } else { acb_hurwitz_zeta(res, s, a, prec); } acb_clear(a); }