LGAMMA
Section: Linux Programmer's Manual (3)
Updated: 2017-09-15
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NAME
lgamma, lgammaf, lgammal, lgamma_r, lgammaf_r, lgammal_r, signgam -
log gamma function
SYNOPSIS
#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
DESCRIPTION
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.
RETURN VALUE
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.
ERRORS
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.
CONFORMING TO
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.
BUGS
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.
SEE ALSO
tgamma(3)
COLOPHON
This page is part of release 4.13 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/.
Index
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- RETURN VALUE
-
- ERRORS
-
- CONFORMING TO
-
- BUGS
-
- SEE ALSO
-
- COLOPHON
-
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