| 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. |
| lgammal() | C11, POSIX.1-2008. |
| signgam | POSIX.1-2008. |
| lgammal_r() | None. |
| lgammal() | C99, POSIX.1-2001. |
| signgam | POSIX.1-2001. |
| lgammal_r() | None. |
NAME
lgamma, lgammaf, lgammal, lgamma_r, lgammaf_r, lgammal_r, signgam - log gamma function
LIBRARY
Math library (libm, -lm)
SYNOPSIS
#include <math.h>double lgamma(double \nx\n);\n
\nfloat lgammaf(float \nx\n);\n
\nlong double lgammal(long double \nx\n);double lgamma_r(double \nx\n, int *\nsignp\n);\n
\nfloat lgammaf_r(float \nx\n, int *\nsignp\n);\n
\nlong double lgammal_r(long double \nx\n, int *\nsignp\n);extern int \nsigngam\n;lgamma\n():
\n
_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L || _XOPEN_SOURCE
\n
|| /* Since glibc 2.19: */ _DEFAULT_SOURCE
\n
|| /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCElgammaf(), lgammal():
\n
_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
\n
|| /* Since glibc 2.19: */ _DEFAULT_SOURCE
\n
|| /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCElgamma_r(), lgammaf_r(), lgammal_r():
\n
/* Since glibc 2.19: */ _DEFAULT_SOURCE
\n
|| /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCEsigngam:
\n
_XOPEN_SOURCE
\n
|| /* Since glibc 2.19: */ _DEFAULT_SOURCE
\n
|| /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCEDESCRIPTION
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.
STANDARDS
- lgamma()
- lgammaf()
- lgammal()
C11, POSIX.1-2008.
- signgam
POSIX.1-2008.
- lgamma_r()
- lgammaf_r()
- lgammal_r()
None.
HISTORY
- lgamma()
- lgammaf()
- lgammal()
C99, POSIX.1-2001.
- signgam
POSIX.1-2001.
- lgamma_r()
- lgammaf_r()
- lgammal_r()
None.
BUGS
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.
SEE ALSO
tgamma(3)