| TGAMMA(3) | Library Functions Manual | TGAMMA(3) |
tgamma, lgamma,
gamma — gamma and log of
gamma
#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);
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>.
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.
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.
The tgamma() , and
lgamma() functions conform to ISO/IEC 9899:2011.
| July 2, 2008 |