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

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

LIBRARY
     Math Library (libm, -lm)

SYNOPSIS
     #include <math.h>

     extern int signgam;

     double
     lgamma(double x);

     float
     lgammaf(float x);

     double
     lgamma_r(double x, int *sign);

     float
     lgammaf_r(float x, int *sign);

     double
     gamma(double x);

     float
     gammaf(float x);

     double
     gamma_r(double x, int *sign);

     float
     gammaf_r(float x, int *sign);

     double
     tgamma(double x);

     float
     tgammaf(float x);

DESCRIPTION
     lgamma(x) returns ln|Γ(x)|.

     The external integer signgam returns the sign of Γ(x).

     lgamma_r() is a reentrant interface that performs identically to
     lgamma(), differing in that the sign of Γ(x) is stored in the location
     pointed to by the sign argument and signgam is not modified.

     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() has returned can signgam be correct.

RETURN VALUES
     lgamma() returns appropriate values unless an argument is out of range.
     Overflow will occur for sufficiently large positive values, and non-posi‐
     tive integers.  For large non-integer negative values, tgamma() will
     underflow.	 On the VAX, the reserved operator is returned, and errno is
     set to ERANGE.

SEE ALSO
     math(3)

HISTORY
     The lgamma function appeared in 4.3BSD.  The tgamma() function appeared
     in NetBSD 6.0.

BSD				  May 4, 2012				   BSD

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