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NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | STANDARDS | HISTORY | BUGS | SEE ALSO | COLOPHON |
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lgamma(3) Library Functions Manual lgamma(3)
lgamma, lgammaf, lgammal, lgamma_r, lgammaf_r, lgammal_r, signgam
- log gamma function
Math library (libm, -lm)
#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;
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 <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
lgammaf(), lgammal():
_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
|| /* Since glibc 2.19: */ _DEFAULT_SOURCE
|| /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
lgamma_r(), lgammaf_r(), lgammal_r():
/* Since glibc 2.19: */ _DEFAULT_SOURCE
|| /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
signgam:
_XOPEN_SOURCE
|| /* Since glibc 2.19: */ _DEFAULT_SOURCE
|| /* glibc <= 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.
lgamma()
lgammaf()
lgammal()
C11, POSIX.1-2008.
signgam
POSIX.1-2008.
lgamma_r()
lgammaf_r()
lgammal_r()
None.
lgamma()
lgammaf()
lgammal()
C99, POSIX.1-2001.
signgam
POSIX.1-2001.
lgamma_r()
lgammaf_r()
lgammal_r()
None.
In glibc 2.9 and earlier, when a pole error occurs, errno is set
to EDOM; instead of the POSIX-mandated ERANGE. Since glibc 2.10,
glibc does the right thing.
tgamma(3)
This page is part of the man-pages (Linux kernel and C library
user-space interface documentation) project. Information about
the project can be found at
⟨https://www.kernel.org/doc/man-pages/⟩. If you have a bug report
for this manual page, see
⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.
This page was obtained from the tarball man-pages-6.15.tar.gz
fetched from
⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on
2025-08-11. If you discover any rendering problems in this HTML
version of the page, or you believe there is a better or more up-
to-date source for the page, or you have corrections or
improvements to the information in this COLOPHON (which is not
part of the original manual page), send a mail to
man-pages@man7.org
Linux man-pages 6.15 2025-05-17 lgamma(3)
Pages that refer to this page: gamma(3), tgamma(3)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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