lgamma, lgammaf, lgammal, lgamma_r, lgammaf_r, lgammal_r — log gamma function
#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) ; |
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Note |
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Compile with −std=c99; 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 non-positive 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.