tgamma, tgammaf, tgammal - true gamma function
#include <math.h>
double tgamma(double
x
);
float tgammaf(float x
);
long double tgammal(long double
x
);
Link with -lm
.
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
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)
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 occurs, 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 mathematical 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.
See math_error(7) for information on how to determine whether an error has occurred when calling these functions.
The following errors can occur:
x
is a negative integer, or negative
infinityerrno
is set to EDOM. An invalid
floating-point exception (FE_INVALID) is raised (but
see BUGS).
x
is +0 or -0errno
is set to ERANGE. A divide-by-zero
floating-point exception (FE_DIVBYZERO) is raised.
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.
An underflow floating-point exception (FE_UNDERFLOW)
is raised, and errno
is set to ERANGE.
These functions first appeared in glibc in version 2.1.
For an explanation of the terms used in this section, see attributes(7).
Interface | Attribute | Value |
tgamma(), tgammaf(), tgammal() | Thread safety | MT-Safe |
C99, POSIX.1-2001, POSIX.1-2008.
Before version 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. x
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.
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