NAME  SYNOPSIS  DESCRIPTION  RETURN VALUE  ERRORS  CONFORMING TO  BUGS  SEE ALSO  COLOPHON 

LGAMMA(3) Linux Programmer's Manual LGAMMA(3)
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 threadsafe, 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 dividebyzero floatingpoint exception (FE_DIVBYZERO) is raised. Range error: result overflow errno is set to ERANGE. An overflow floatingpoint exception (FE_OVERFLOW) is raised.
The lgamma() functions are specified in C99, POSIX.12001, and POSIX.12008. signgam is specified in POSIX.12001 and POSIX.12008, 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 POSIXmandated ERANGE. Since version 2.10, glibc does the right thing.
tgamma(3)
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20170915 LGAMMA(3)
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