lgamma, lgammaf, lgammal, lgamma_r, lgammaf_r, lgammal_r, signgam - log gamma function
#include <math.h>
double lgamma(double x);
float lgammaf(float x);
long double lgammal(long double x);
double lgamma_r(double x, int *signp);
float lgammaf_r(float x, int *signp);
long double lgammal_r(long double x, int *signp);
extern int signgam;
Link with -lm
.
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
lgamma():
_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L || _XOPEN_SOURCE || /* Since glibc 2.19: */ _DEFAULT_SOURCE || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L || /* Since glibc 2.19: */ _DEFAULT_SOURCE || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
lgamma_r(), lgammaf_r(), lgammal_r():
/* Since glibc 2.19: */ _DEFAULT_SOURCE || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
signgam
:
_XOPEN_SOURCE || /* Since glibc 2.19: */ _DEFAULT_SOURCE || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
For the definition of the Gamma function, see tgamma(3).
The lgamma(), lgammaf(), and
lgammal() functions return the natural logarithm of the
absolute value of the Gamma function. The sign of the Gamma function is
returned in the external integer signgam
declared in
<math.h>
. It is 1 when the Gamma function is positive or
zero, -1 when it is negative.
Since using a constant location signgam
is not thread-safe,
the functions lgamma_r(), lgammaf_r(),
and lgammal_r() have been introduced; they return the
sign via the argument signp
.
On success, these functions return the natural logarithm of Gamma(x).
If x
is a NaN, a NaN is returned.
If x
is 1 or 2, +0 is returned.
If x
is positive infinity or negative infinity, positive
infinity is returned.
If x
is a nonpositive integer, a pole error occurs, and the
functions return +HUGE_VAL,
+HUGE_VALF, or +HUGE_VALL,
respectively.
If the result overflows, a range error occurs, and the functions return HUGE_VAL, HUGE_VALF, or HUGE_VALL, respectively, with the correct mathematical sign.
See math_error(7) for information on how to determine whether an error has occurred when calling these functions.
The following errors can occur:
x
is a nonpositive integererrno
is set to ERANGE (but see BUGS). A
divide-by-zero floating-point exception (FE_DIVBYZERO)
is raised.
errno
is set to ERANGE. An overflow
floating-point exception (FE_OVERFLOW) is raised.
In glibc 2.9 and earlier, when a pole error occurs, errno
is
set to EDOM; instead of the POSIX-mandated
ERANGE. Since version 2.10, glibc does the right
thing.
tgamma(3)
This page is part of release 5.10 of the Linux man-pages
project. A description of the project, information about reporting bugs,
and the latest version of this page, can be found at
https://www.kernel.org/doc/man-pages/.