Originální popis anglicky:
lgamma, lgammaf, lgammal, lgamma_r, lgammaf_r, lgammal_r - log gamma function
Návod, kniha: Linux Programmer's Manual
#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);
Link with -lm.
For the definition of the Gamma function, see
tgamma(3).
The
lgamma() function returns 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() etc. have been introduced; they return this sign via the
parameter
signp.
For nonpositive integer values of
x,
lgamma() returns HUGE_VAL,
sets
errno to ERANGE and raises the zero divide exception. (Similarly,
lgammaf() returns HUGE_VALF and
lgammal() returns HUGE_VALL.)
In order to check for errors, set
errno to zero and call
feclearexcept(FE_ALL_EXCEPT) before calling these functions. On return,
if
errno is non-zero or
fetestexcept(FE_INVALID | FE_DIVBYZERO |
FE_OVERFLOW | FE_UNDERFLOW) is non-zero, an error has occurred.
A range error occurs if x is too large. A pole error occurs if x is a negative
integer or zero.
C99, SVID 3, BSD 4.3
tgamma(3)
