/* 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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