/* 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); }
void acb_dirichlet_zeta_rs_mid(acb_t res, const acb_t s, slong K, slong prec) { acb_t R1, R2, X, t; slong wp; if (arf_sgn(arb_midref(acb_imagref(s))) < 0) { acb_init(t); acb_conj(t, s); acb_dirichlet_zeta_rs(res, t, K, prec); acb_conj(res, res); acb_clear(t); return; } acb_init(R1); acb_init(R2); acb_init(X); acb_init(t); /* rs_r increases the precision internally */ wp = prec; acb_dirichlet_zeta_rs_r(R1, s, K, wp); if (arb_is_exact(acb_realref(s)) && (arf_cmp_2exp_si(arb_midref(acb_realref(s)), -1) == 0)) { acb_conj(R2, R1); } else { /* conj(R(conj(1-s))) */ arb_sub_ui(acb_realref(t), acb_realref(s), 1, 10 * wp); arb_neg(acb_realref(t), acb_realref(t)); arb_set(acb_imagref(t), acb_imagref(s)); acb_dirichlet_zeta_rs_r(R2, t, K, wp); acb_conj(R2, R2); } if (acb_is_finite(R1) && acb_is_finite(R2)) { wp += 10 + arf_abs_bound_lt_2exp_si(arb_midref(acb_imagref(s))); wp = FLINT_MAX(wp, 10); /* X = pi^(s-1/2) gamma((1-s)/2) rgamma(s/2) = (2 pi)^s rgamma(s) / (2 cos(pi s / 2)) */ acb_rgamma(X, s, wp); acb_const_pi(t, wp); acb_mul_2exp_si(t, t, 1); acb_pow(t, t, s, wp); acb_mul(X, X, t, wp); acb_mul_2exp_si(t, s, -1); acb_cos_pi(t, t, wp); acb_mul_2exp_si(t, t, 1); acb_div(X, X, t, wp); acb_mul(R2, R2, X, wp); } /* R1 + X * R2 */ acb_add(res, R1, R2, prec); acb_clear(R1); acb_clear(R2); acb_clear(X); acb_clear(t); }