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/* specfunc/gsl_sf_dilog.h
*
* Copyright (C) 1996, 1997, 1998, 1999, 2000, 2004 Gerard Jungman
*
* This program 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.
*
* This program 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 this program; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
*/
/* Author: G. Jungman */
#ifndef __GSL_SF_DILOG_H__
#define __GSL_SF_DILOG_H__
#include <gsl/gsl_sf_result.h>
#undef __BEGIN_DECLS
#undef __END_DECLS
#ifdef __cplusplus
# define __BEGIN_DECLS extern "C" {
# define __END_DECLS }
#else
# define __BEGIN_DECLS /* empty */
# define __END_DECLS /* empty */
#endif
__BEGIN_DECLS
/* Real part of DiLogarithm(x), for real argument.
* In Lewin's notation, this is Li_2(x).
*
* Li_2(x) = - Re[ Integrate[ Log[1-s] / s, {s, 0, x}] ]
*
* The function in the complex plane has a branch point
* at z = 1; we place the cut in the conventional way,
* on [1, +infty). This means that the value for real x > 1
* is a matter of definition; however, this choice does not
* affect the real part and so is not relevant to the
* interpretation of this implemented function.
*/
int gsl_sf_dilog_e(const double x, gsl_sf_result * result);
double gsl_sf_dilog(const double x);
/* DiLogarithm(z), for complex argument z = x + i y.
* Computes the principal branch.
*
* Recall that the branch cut is on the real axis with x > 1.
* The imaginary part of the computed value on the cut is given
* by -Pi*log(x), which is the limiting value taken approaching
* from y < 0. This is a conventional choice, though there is no
* true standardized choice.
*
* Note that there is no canonical way to lift the defining
* contour to the full Riemann surface because of the appearance
* of a "hidden branch point" at z = 0 on non-principal sheets.
* Experts will know the simple algebraic prescription for
* obtaining the sheet they want; non-experts will not want
* to know anything about it. This is why GSL chooses to compute
* only on the principal branch.
*/
int
gsl_sf_complex_dilog_xy_e(
const double x,
const double y,
gsl_sf_result * result_re,
gsl_sf_result * result_im
);
/* DiLogarithm(z), for complex argument z = r Exp[i theta].
* Computes the principal branch, thereby assuming an
* implicit reduction of theta to the range (-2 pi, 2 pi).
*
* If theta is identically zero, the imaginary part is computed
* as if approaching from y > 0. For other values of theta no
* special consideration is given, since it is assumed that
* no other machine representations of multiples of pi will
* produce y = 0 precisely. This assumption depends on some
* subtle properties of the machine arithmetic, such as
* correct rounding and monotonicity of the underlying
* implementation of sin() and cos().
*
* This function is ok, but the interface is confusing since
* it makes it appear that the branch structure is resolved.
* Furthermore the handling of values close to the branch
* cut is subtle. Perhap this interface should be deprecated.
*/
int
gsl_sf_complex_dilog_e(
const double r,
const double theta,
gsl_sf_result * result_re,
gsl_sf_result * result_im
);
/* Spence integral; spence(s) := Li_2(1-s)
*
* This function has a branch point at 0; we place the
* cut on (-infty,0). Because of our choice for the value
* of Li_2(z) on the cut, spence(s) is continuous as
* s approaches the cut from above. In other words,
* we define spence(x) = spence(x + i 0+).
*/
int
gsl_sf_complex_spence_xy_e(
const double x,
const double y,
gsl_sf_result * real_sp,
gsl_sf_result * imag_sp
);
__END_DECLS
#endif /* __GSL_SF_DILOG_H__ */
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