LGAMMASection: Linux Programmer's Manual (3)
Index Return to Main Contents
NAMElgamma, 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)):
_BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE || _ISOC99_SOURCE; or
lgammaf(), lgammal(): _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 600 || _ISOC99_SOURCE; or cc -std=c99
lgamma_r(), lgammaf_r(), lgammal_r(): _BSD_SOURCE || _SVID_SOURCE
signgam: _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE
DESCRIPTIONFor the definition of the Gamma function, see tgamma(3).
The lgamma() function returns 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.
RETURN VALUEOn 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 non-positive integer, a pole error occurs, and the functions return +HUGE_VAL, +HUGE_VALF, or +HUGE_VALL, respectively.
ERRORSSee 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 non-positive 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.
CONFORMING TOThe lgamma() functions are specified in C99 and POSIX.1-2001. signgam is specified in POSIX.1-2001, but not in C99. The lgamma_r() functions are non-standard, but present on several other systems.
BUGSFor a pole error, errno is set to EDOM; POSIX.1 says it should be set to ERANGE.
COLOPHONThis page is part of release 3.21 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.