TGAMMA(3)						   BSD Library Functions Manual 						 TGAMMA(3)

NAME

     tgamma, lgamma, gamma -- gamma and log of gamma

SYNOPSIS

     #include <math.h>

     double
     tgamma(double x);

     long double
     tgammal(long double x);

     float
     tgammaf(float x);

     double
     lgamma_r(double x, int *psigngam);

     long double
     lgammal_r(long double x, int *psigngam);

     float
     lgammaf_r(float x, int *psigngam);

     double
     lgamma(double x);

     long double
     lgammal(long double x);

     float
     lgammaf(float x);

DESCRIPTION

     tgamma() calculates the gamma function of x.  lgamma() calculates the natural logorithm of the absolute value of the gamma function of x.
     gamma() is the same function as tgamma. Its use is deprecated.

     lgamma_r() is a thread-safe alternative to lgamma().  Instead of setting the global variable signgam, it stores the sign of Gamma(x) in the
     location pointed to by its second argument.  In order to use the lgamma_r() function, define the macro _REENTRANT before including <math.h>.

SPECIAL VALUES

     tgamma(+-0) returns +-infinity and raises the "divide-by-zero" floating-point exception.

     tgamma(x) returns a NaN and raises the "invalid" floating-point exception if x is a negative integer.

     tgamma(-infinity) returns a NaN and raises the "invalid" floating-point exception.

     tgamma(+infinity) returns +infinity.

     tgamma(x) generates a domain error if x is a negative integer or if the result cannnot be respresented when x is 0.

     A range error may occur if the magnitude of x is too large or too small.

     lgamma(1) returns +0.

     lgamma(2) returns +0.

     lgamma(x) returns +infinity and raises the "divide-by-zero" floating-point exception if x is a negative integer or 0.

     lgamma(+-infinity) returns +infinity.

     lgamma(x) generates a range error if x is too large.

     A range error may occur if x is a negative integer or 0.

NOTE

     lgamma(x) and its variants have the (non-threadsafe) side-effect of setting the global variable signgam to +-1, equal to the sign of
     tgamma(x).  lgamma_r(x, psigngam) instead sets the user-allocated integer pointed to by the psigngam argument.

     gamma() and gamma_r() are deprecated, and should not be used.  The tgamma() function should be used instead.  Note, however, that on some
     platforms, gamma() and 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 lgamma() or lgamma_r() instead.

SEE ALSO

     math(3)

STANDARDS

     The tgamma() , and lgamma() functions conform to ISO/IEC 9899:2011.

								   July 02, 2008