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/*
Copyright (C) 2015 Fredrik Johansson
This file is part of FLINT.
FLINT is free software: you can redistribute it and/or modify it under
the terms of the GNU Lesser General Public License (LGPL) as published
by the Free Software Foundation; either version 3 of the License, or
(at your option) any later version. See <https://www.gnu.org/licenses/>.
*/
#include "acb.h"
#include "acb_poly.h"
void
acb_polygamma(acb_t res, const acb_t s, const acb_t z, slong prec)
{
if (acb_is_zero(s))
{
acb_digamma(res, z, prec);
}
else if (acb_is_int(s) && arb_is_positive(acb_realref(s)))
{
acb_t t, u;
acb_init(t);
acb_init(u);
acb_add_ui(t, s, 1, prec);
acb_gamma(u, t, prec);
acb_hurwitz_zeta(t, t, z, prec);
if (acb_is_int_2exp_si(s, 1))
acb_neg(t, t);
acb_mul(res, t, u, prec);
acb_clear(t);
acb_clear(u);
}
else
{
acb_t t, u;
acb_struct v[2];
acb_init(t);
acb_init(u);
acb_init(v);
acb_init(v + 1);
/* u = psi(-s) + gamma */
acb_neg(t, s);
acb_digamma(u, t, prec);
arb_const_euler(acb_realref(v), prec);
arb_add(acb_realref(u), acb_realref(u), acb_realref(v), prec);
acb_add_ui(t, s, 1, prec);
_acb_poly_zeta_cpx_series(v, t, z, 0, 2, prec);
acb_addmul(v + 1, v, u, prec);
acb_neg(t, s);
acb_rgamma(u, t, prec);
acb_mul(res, v + 1, u, prec);
acb_clear(v);
acb_clear(v + 1);
acb_clear(t);
acb_clear(u);
}
}