lgamma(3) -- Linux man page
NAME
lgamma, lgammaf, lgammal, lgamma_r, lgammaf_r, lgammal_r - 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);
DESCRIPTION
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.)
ERRORS
An application wishing to check for error situations should 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.
CONFORMING TO
C99, SVID 3, BSD 4.3
SEE ALSO
tgamma(3)
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