void
_acb_poly_zeta_cpx_reflect(acb_ptr t, const acb_t h, const acb_t a, int deflate, slong len, slong prec)
{
/* use reflection formula */
if (arf_sgn(arb_midref(acb_realref(h))) < 0 && acb_is_one(a))
{
/* zeta(s) = (2*pi)**s * sin(pi*s/2) / pi * gamma(1-s) * zeta(1-s) */
acb_t pi, hcopy;
acb_ptr f, s1, s2, s3, s4, u;
slong i;
acb_init(pi);
acb_init(hcopy);
f = _acb_vec_init(2);
s1 = _acb_vec_init(len);
s2 = _acb_vec_init(len);
s3 = _acb_vec_init(len);
s4 = _acb_vec_init(len);
u = _acb_vec_init(len);
acb_set(hcopy, h);
acb_const_pi(pi, prec);
/* s1 = (2*pi)**s */
acb_mul_2exp_si(pi, pi, 1);
_acb_poly_pow_cpx(s1, pi, h, len, prec);
acb_mul_2exp_si(pi, pi, -1);
/* s2 = sin(pi*s/2) / pi */
acb_set(f, h);
acb_one(f + 1);
acb_mul_2exp_si(f, f, -1);
acb_mul_2exp_si(f + 1, f + 1, -1);
_acb_poly_sin_pi_series(s2, f, 2, len, prec);
_acb_vec_scalar_div(s2, s2, len, pi, prec);
/* s3 = gamma(1-s) */
acb_sub_ui(f, hcopy, 1, prec);
acb_neg(f, f);
acb_set_si(f + 1, -1);
_acb_poly_gamma_series(s3, f, 2, len, prec);
/* s4 = zeta(1-s) */
acb_sub_ui(f, hcopy, 1, prec);
acb_neg(f, f);
_acb_poly_zeta_cpx_series(s4, f, a, 0, len, prec);
for (i = 1; i < len; i += 2)
acb_neg(s4 + i, s4 + i);
_acb_poly_mullow(u, s1, len, s2, len, len, prec);
_acb_poly_mullow(s1, s3, len, s4, len, len, prec);
_acb_poly_mullow(t, u, len, s1, len, len, prec);
/* add 1/(1-(s+t)) = 1/(1-s) + t/(1-s)^2 + ... */
if (deflate)
{
acb_sub_ui(u, hcopy, 1, prec);
acb_neg(u, u);
acb_inv(u, u, prec);
for (i = 1; i < len; i++)
acb_mul(u + i, u + i - 1, u, prec);
_acb_vec_add(t, t, u, len, prec);
}
acb_clear(pi);
acb_clear(hcopy);
_acb_vec_clear(f, 2);
_acb_vec_clear(s1, len);
_acb_vec_clear(s2, len);
_acb_vec_clear(s3, len);
_acb_vec_clear(s4, len);
_acb_vec_clear(u, len);
}
else
{
_acb_poly_zeta_cpx_series(t, h, a, deflate, len, prec);
}
}
void
_acb_poly_rgamma_series(acb_ptr res, acb_srcptr h, slong hlen, slong len, slong prec)
{
int reflect;
slong i, rflen, r, n, wp;
acb_ptr t, u, v;
acb_struct f[2];
hlen = FLINT_MIN(hlen, len);
if (hlen == 1)
{
acb_rgamma(res, h, prec);
_acb_vec_zero(res + 1, len - 1);
return;
}
/* use real code for real input */
if (_acb_vec_is_real(h, hlen))
{
arb_ptr tmp = _arb_vec_init(len);
for (i = 0; i < hlen; i++)
arb_set(tmp + i, acb_realref(h + i));
_arb_poly_rgamma_series(tmp, tmp, hlen, len, prec);
for (i = 0; i < len; i++)
acb_set_arb(res + i, tmp + i);
_arb_vec_clear(tmp, len);
return;
}
wp = prec + FLINT_BIT_COUNT(prec);
t = _acb_vec_init(len);
u = _acb_vec_init(len);
v = _acb_vec_init(len);
acb_init(f);
acb_init(f + 1);
/* otherwise use Stirling series */
acb_gamma_stirling_choose_param(&reflect, &r, &n, h, 1, 0, wp);
/* rgamma(h) = (gamma(1-h+r) sin(pi h)) / (rf(1-h, r) * pi), h = h0 + t*/
if (reflect)
{
/* u = gamma(r+1-h) */
acb_sub_ui(f, h, r + 1, wp);
acb_neg(f, f);
_acb_poly_gamma_stirling_eval(t, f, n, len, wp);
_acb_poly_exp_series(u, t, len, len, wp);
for (i = 1; i < len; i += 2)
acb_neg(u + i, u + i);
/* v = sin(pi x) */
acb_set(f, h);
acb_one(f + 1);
_acb_poly_sin_pi_series(v, f, 2, len, wp);
_acb_poly_mullow(t, u, len, v, len, len, wp);
/* rf(1-h,r) * pi */
if (r == 0)
{
acb_const_pi(u, wp);
_acb_vec_scalar_div(v, t, len, u, wp);
}
else
{
acb_sub_ui(f, h, 1, wp);
acb_neg(f, f);
acb_set_si(f + 1, -1);
rflen = FLINT_MIN(len, r + 1);
_acb_poly_rising_ui_series(v, f, FLINT_MIN(2, len), r, rflen, wp);
acb_const_pi(u, wp);
_acb_vec_scalar_mul(v, v, rflen, u, wp);
/* divide by rising factorial */
/* TODO: might better to use div_series, when it has a good basecase */
_acb_poly_inv_series(u, v, rflen, len, wp);
_acb_poly_mullow(v, t, len, u, len, len, wp);
}
}
else
{
/* rgamma(h) = rgamma(h+r) rf(h,r) */
if (r == 0)
{
acb_add_ui(f, h, r, wp);
_acb_poly_gamma_stirling_eval(t, f, n, len, wp);
_acb_vec_neg(t, t, len);
_acb_poly_exp_series(v, t, len, len, wp);
}
else
{
acb_set(f, h);
acb_one(f + 1);
rflen = FLINT_MIN(len, r + 1);
_acb_poly_rising_ui_series(t, f, FLINT_MIN(2, len), r, rflen, wp);
acb_add_ui(f, h, r, wp);
_acb_poly_gamma_stirling_eval(v, f, n, len, wp);
_acb_vec_neg(v, v, len);
_acb_poly_exp_series(u, v, len, len, wp);
_acb_poly_mullow(v, u, len, t, rflen, len, wp);
}
}
/* compose with nonconstant part */
acb_zero(t);
_acb_vec_set(t + 1, h + 1, hlen - 1);
_acb_poly_compose_series(res, v, len, t, hlen, len, prec);
acb_clear(f);
acb_clear(f + 1);
_acb_vec_clear(t, len);
_acb_vec_clear(u, len);
_acb_vec_clear(v, len);
}
void
_acb_poly_zeta_em_tail_naive(acb_ptr sum, const acb_t s, const acb_t Na, acb_srcptr Nasx, slong M, slong d, slong prec)
{
acb_ptr u, term;
acb_t Na2, splus, rec;
arb_t x;
fmpz_t c;
int aint;
slong r;
BERNOULLI_ENSURE_CACHED(2 * M);
u = _acb_vec_init(d);
term = _acb_vec_init(d);
acb_init(splus);
acb_init(rec);
acb_init(Na2);
arb_init(x);
fmpz_init(c);
_acb_vec_zero(sum, d);
/* u = 1/2 * Nasx */
_acb_vec_scalar_mul_2exp_si(u, Nasx, d, -WORD(1));
/* term = u * (s+x) / (N+a) */
_acb_poly_mullow_cpx(u, u, d, s, d, prec);
_acb_vec_scalar_div(term, u, d, Na, prec);
/* (N+a)^2 or 1/(N+a)^2 */
acb_mul(Na2, Na, Na, prec);
aint = acb_is_int(Na2);
if (!aint)
acb_inv(Na2, Na2, prec);
for (r = 1; r <= M; r++)
{
/* flint_printf("sum 2: %wd %wd\n", r, M); */
/* sum += bernoulli number * term */
arb_set_round_fmpz(x, fmpq_numref(bernoulli_cache + 2 * r), prec);
arb_div_fmpz(x, x, fmpq_denref(bernoulli_cache + 2 * r), prec);
_acb_vec_scalar_mul_arb(u, term, d, x, prec);
_acb_vec_add(sum, sum, u, d, prec);
/* multiply term by ((s+x)+2r-1)((s+x)+2r) / ((N+a)^2 * (2*r+1)*(2*r+2)) */
acb_set(splus, s);
arb_add_ui(acb_realref(splus), acb_realref(splus), 2*r-1, prec);
_acb_poly_mullow_cpx(term, term, d, splus, d, prec);
arb_add_ui(acb_realref(splus), acb_realref(splus), 1, prec);
_acb_poly_mullow_cpx(term, term, d, splus, d, prec);
/* TODO: combine with previous multiplication? */
if (aint)
{
arb_mul_ui(x, acb_realref(Na2), 2*r+1, prec);
arb_mul_ui(x, x, 2*r+2, prec);
_acb_vec_scalar_div_arb(term, term, d, x, prec);
}
else
{
fmpz_set_ui(c, 2*r+1);
fmpz_mul_ui(c, c, 2*r+2);
acb_div_fmpz(rec, Na2, c, prec);
_acb_vec_scalar_mul(term, term, d, rec, prec);
}
}
_acb_vec_clear(u, d);
_acb_vec_clear(term, d);
acb_clear(splus);
acb_clear(rec);
acb_clear(Na2);
arb_clear(x);
fmpz_clear(c);
}
