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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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