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LGAMMA(3)		 BSD Library Functions Manual		     LGAMMA(3)

NAME
     lgamma, lgamma_r, lgammaf, lgammaf_r, gamma, gamma_r, gammaf, gammaf_r,
     tgamma, tgammaf — log gamma functions, gamma function

LIBRARY
     Math Library (libm, -lm)

SYNOPSIS
     #include <math.h>

     extern int signgam;

     double
     lgamma(double x);

     double
     lgamma_r(double x, int *signgamp);

     float
     lgammaf(float x);

     float
     lgammaf_r(float x, int *signgamp);

     double
     gamma(double x);

     double
     gamma_r(double x, int *signgamp);

     float
     gammaf(float x);

     float
     gammaf_r(float x, int *signgamp);

     double
     tgamma(double x);

     float
     tgammaf(float x);

DESCRIPTION
     lgamma(x) and lgammaf(x) return ln|Γ(x)|.	The external integer signgam
     returns the sign of Γ(x).

     lgamma_r(x, signgamp) and lgammaf_r(x, signgamp) provide the same func‐
     tionality as lgamma(x) and lgammaf(x) but the caller must provide an
     integer to store the sign of Γ(x).

     The tgamma(x) and tgammaf(x) functions return Γ(x), with no effect on
     signgam.

     gamma(), gammaf(), gamma_r(), and gammaf_r() are deprecated aliases for
     lgamma(), lgammaf(), lgamma_r(), and lgammaf_r(), respectively.

IDIOSYNCRASIES
     Do not use the expression “signgam∗exp(lgamma(x))” to compute g := Γ(x).
     Instead use a program like this (in C):

	   lg = lgamma(x); g = signgam∗exp(lg);

     Only after lgamma() or lgammaf() has returned can signgam be correct.

     For arguments in its range, tgamma() is preferred, as for positive argu‐
     ments it is accurate to within one unit in the last place.	 Exponentia‐
     tion of lgamma() will lose up to 10 significant bits.

RETURN VALUES
     gamma(), gamma_r(), gammaf(), gammaf_r(), lgamma(), lgamma_r(),
     lgammaf(), and lgammaf_r() return appropriate values unless an argument
     is out of range.  Overflow will occur for sufficiently large positive
     values, and non-positive integers.	 For large non-integer negative val‐
     ues, tgamma() will underflow.

SEE ALSO
     math(3)

STANDARDS
     The lgamma(), lgammaf(), tgamma(), and tgammaf() functions are expected
     to conform to ISO/IEC 9899:1999 (“ISO C99”).

HISTORY
     The lgamma() function appeared in 4.3BSD.	The gamma() function appeared
     in 4.4BSD as a function which computed Γ(x).  This version was used in
     FreeBSD 1.1.  The name gamma() was originally dedicated to the lgamma()
     function, and that usage was restored by switching to Sun's fdlibm in
     FreeBSD 1.1.5.  The tgamma() function appeared in FreeBSD 5.0.

BSD			       January 14, 2005				   BSD

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