GNU/Linux man pages
Livre :
Expressions régulières,
Syntaxe et mise en oeuvre :
GNU/Linux |
RedHat 9.0(Shrike) |
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lgammaf(3) |
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lgamma − 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);
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)
For x < 0.5 one can use
Gamma(x) * Gamma(1-x) = PI/sin(PI*x)
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.)
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.
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ERANGE |
Invalid argument - nonpositive integer value of x. |
C99, SVID 3, BSD 4.3
tgamma(3)
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lgammaf(3) | |