tgamma(3) Library Functions Manual tgamma(3)
NAME
tgamma, tgammaf, tgammal - true gamma function
LIBRARY
Math library (libm, -lm)
SYNOPSIS
#include <math.h>
double tgamma(double x);
float tgammaf(float x);
long double tgammal(long double x);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
tgamma(), tgammaf(), tgammal():
_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
DESCRIPTION
These functions calculate the Gamma function of x.
The Gamma function is defined by
Gamma(x) = integral from 0 to infinity of t^(x-1) e^-t dt
It is defined for every real number except for nonpositive integers.
For nonnegative integral m one has
Gamma(m+1) = m!
and, more generally, for all x:
Gamma(x+1) = x * Gamma(x)
Furthermore, the following is valid for all values of x outside the
poles:
Gamma(x) * Gamma(1 - x) = PI / sin(PI * x)
RETURN VALUE
On success, these functions return Gamma(x).
If x is a NaN, a NaN is returned.
If x is positive infinity, positive infinity is returned.
If x is a negative integer, or is negative infinity, a domain error oc-
curs, and a NaN is returned.
If the result overflows, a range error occurs, and the functions return
HUGE_VAL, HUGE_VALF, or HUGE_VALL, respectively, with the correct mathe-
matical sign.
If the result underflows, a range error occurs, and the functions return
0, with the correct mathematical sign.
If x is -0 or +0, a pole error occurs, and the functions return
HUGE_VAL, HUGE_VALF, or HUGE_VALL, respectively, with the same sign as
the 0.
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:
Domain error: x is a negative integer, or negative infinity
errno is set to EDOM. An invalid floating-point exception
(FE_INVALID) is raised (but see BUGS).
Pole error: x is +0 or -0
errno is set to ERANGE. A divide-by-zero floating-point excep-
tion (FE_DIVBYZERO) is raised.
Range error: result overflow
errno is set to ERANGE. An overflow floating-point exception
(FE_OVERFLOW) is raised.
glibc also gives the following error which is not specified in C99 or
POSIX.1-2001.
Range error: result underflow
An underflow floating-point exception (FE_UNDERFLOW) is raised,
and errno is set to ERANGE.
ATTRIBUTES
For an explanation of the terms used in this section, see attributes(7).
┌────────────────────────────────────────────┬───────────────┬─────────┐
│ Interface │ Attribute │ Value │
├────────────────────────────────────────────┼───────────────┼─────────┤
│ tgamma(), tgammaf(), tgammal() │ Thread safety │ MT-Safe │
└────────────────────────────────────────────┴───────────────┴─────────┘
STANDARDS
C11, POSIX.1-2008.
HISTORY
glibc 2.1. C99, POSIX.1-2001.
NOTES
This function had to be called "true gamma function" since there is al-
ready a function gamma(3) that returns something else (see gamma(3) for
details).
BUGS
Before glibc 2.18, the glibc implementation of these functions did not
set errno to EDOM when x is negative infinity.
Before glibc 2.19, the glibc implementation of these functions did not
set errno to ERANGE on an underflow range error.
In glibc versions 2.3.3 and earlier, an argument of +0 or -0 incorrectly
produced a domain error (errno set to EDOM and an FE_INVALID exception
raised), rather than a pole error.
SEE ALSO
gamma(3), lgamma(3)
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