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
lgammaf(),
lgammal():
_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:
- Pole error: x is a nonpositive integer
- errno is set to ERANGE (but see BUGS). A divide-by-zero
floating-point exception (FE_DIVBYZERO) is raised.
- Range error: result overflow
- errno is set to ERANGE. An overflow floating-point exception
(FE_OVERFLOW) is raised.
The
lgamma() functions are specified in C99, POSIX.1-2001, and
POSIX.1-2008.
signgam is specified in POSIX.1-2001 and POSIX.1-2008,
but not in C99. The
lgamma_r() functions are nonstandard, but present
on several other systems.
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)