arb/acb_dirichlet/gauss_sum_theta.c

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2016-04-12 15:07:04 +02:00
/*=============================================================================
This file is part of ARB.
ARB is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.
ARB is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with ARB; if not, write to the Free Software
Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
=============================================================================*/
/******************************************************************************
Copyright (C) 2016 Pascal Molin
******************************************************************************/
#include "acb_dirichlet.h"
void
acb_dirichlet_gauss_sum_theta(acb_t res, const acb_dirichlet_group_t G, const acb_dirichlet_char_t chi, slong prec)
{
arb_t x;
acb_t eps;
arb_init(x);
if ((G->q == 300 && (chi->n == 271 || chi->n == 131))
|| (G->q == 600 && (chi->n == 11 || chi->n == 91)))
{
/* or could use l'Hopital rule */
acb_dirichlet_gauss_sum_naive(res, G, chi, prec);
return;
}
arb_one(x);
acb_dirichlet_chi_theta(res, G, chi, x, prec);
acb_init(eps);
acb_conj(eps, res);
acb_div(eps, res, eps, prec);
if (chi->parity)
{
arb_zero(acb_realref(res));
arb_sqrt_ui(acb_imagref(res), G->q, prec);
}
else
{
arb_zero(acb_imagref(res));
arb_sqrt_ui(acb_realref(res), G->q, prec);
}
acb_mul(res, res, eps, prec);
arb_clear(x);
acb_clear(eps);
}