.\" Copyright (c) 1985, 1991 Regents of the University of California. .\" All rights reserved. .\" .\" Redistribution and use in source and binary forms, with or without .\" modification, are permitted provided that the following conditions .\" are met: .\" 1. Redistributions of source code must retain the above copyright .\" notice, this list of conditions and the following disclaimer. .\" 2. Redistributions in binary form must reproduce the above copyright .\" notice, this list of conditions and the following disclaimer in the .\" documentation and/or other materials provided with the distribution. .\" 3. All advertising materials mentioning features or use of this software .\" must display the following acknowledgement: .\" This product includes software developed by the University of .\" California, Berkeley and its contributors. .\" 4. Neither the name of the University nor the names of its contributors .\" may be used to endorse or promote products derived from this software .\" without specific prior written permission. .\" .\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND .\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE .\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE .\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE .\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS .\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF .\" SUCH DAMAGE. .\" .\" from: @(#)erf.3 6.4 (Berkeley) 4/20/91 .\" $Id: tgamma.3,v 1.4 2004/12/20 21:35:46 scp Exp $ .\" .Dd July 02, 2008 .Dt TGAMMA 3 .Sh NAME .Nm tgamma , .Nm lgamma , .Nm gamma .Nd gamma and log of gamma .Sh SYNOPSIS .Fd #include <math.h> .Ft double .Fn tgamma "double x" .Ft long double .Fn tgammal "long double x" .Ft float .Fn tgammaf "float x" .Ft double .Fn lgamma_r "double x, int *psigngam" .Ft long double .Fn lgammal_r "long double x, int *psigngam" .Ft float .Fn lgammaf_r "float x, int *psigngam" .Ft double .Fn lgamma "double x" .Ft long double .Fn lgammal "long double x" .Ft float .Fn lgammaf "float x" .Sh DESCRIPTION .Fn tgamma calculates the gamma function of x. .Fn lgamma calculates the natural logorithm of the absolute value of the gamma function of x. .Fn gamma is the same function as tgamma. Its use is deprecated. .Pp .Fn lgamma_r is a thread-safe alternative to .Fn lgamma . Instead of setting the global variable .Fa signgam , it stores the sign of Gamma(x) in the location pointed to by its second argument. In order to use the .Fn lgamma_r function, define the macro _REENTRANT before including <math.h>. .Sh SPECIAL VALUES .Fn tgamma "±0" returns ±infinity and raises the "divide-by-zero" floating-point exception. .Pp .Fn tgamma "x" returns a NaN and raises the "invalid" floating-point exception if x is a negative integer. .Pp .Fn tgamma "-infinity" returns a NaN and raises the "invalid" floating-point exception. .Pp .Fn tgamma "+infinity" returns +infinity. .Pp .Fn tgamma "x" generates a domain error if x is a negative integer or if the result cannnot be respresented when x is 0. .Pp A range error may occur if the magnitude of x is too large or too small. .Pp .Fn lgamma "1" returns +0. .Pp .Fn lgamma "2" returns +0. .Pp .Fn lgamma "x" returns +infinity and raises the "divide-by-zero" floating-point exception if x is a negative integer or 0. .Pp .Fn lgamma "±infinity" returns +infinity. .Pp .Fn lgamma "x" generates a range error if x is too large. .Pp A range error may occur if x is a negative integer or 0. .Sh NOTE .Fn lgamma "x" and its variants have the (non-threadsafe) side-effect of setting the global variable .Fa signgam to ±1, equal to the sign of .Fn tgamma "x" . .Fn lgamma_r "x, psigngam" instead sets the user-allocated integer pointed to by the .Fa psigngam argument. .Pp .Fn gamma and .Fn gamma_r are deprecated, and should not be used. The .Fn tgamma function should be used instead. Note, however, that on some platforms, .Fn gamma and .Fn gamma_r historically computed the log of the Gamma function, instead of the Gamma function itself. When porting code from such platforms, it will be necessary to use .Fn lgamma or .Fn lgamma_r instead. .Sh SEE ALSO .Xr math 3 .Sh STANDARDS The .Fn tgamma , and .Fn lgamma functions conform to ISO/IEC 9899:1999(E).