lgamma函数怎么调用，找不到库函数

[caoeryingzi]

vc中，要调用lgamma函数，可是，调用了math.h之后，仍然无法识别。

我想问一下这个函数如何调用。谢谢

[老邓]

Format

#define _XOPEN_SOURCE
#include <math.h>

double lgamma(double x);
extern int signgam;
int *__signgam(void);C99

#define _ISOC99_SOURCE
#include <math.h>

double lgamma(double x);
float lgammaf(float x);
long double lgammal(long double x);

[老邓]

GCC 4.4通过：

#include <math.h>
#include <stdio.h>

int main(void)
{
   double x=42, g_at_x;

   g_at_x = exp(lgamma(x));       /* g_at_x = 3.345253e+49 */
   printf ("The value of G(%4.2f) is %7.2e\n", x, g_at_x);
   return 0;
}

输出：
The value of G(42.00) is 3.35e+049

Process returned 0 (0x0) execution time : 0.094 s
Press any key to continue.

[lingyin55]

*nix 数学库里面有lgamma. 是log gamma. 如果你加了windows下面的math库还Link不到的话，那就自己编一个好了。下面是lgamma实现的功能。


NAME
lgamma - 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
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 func-
tions 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.)

CONFORMING TO
C99, SVID 3, BSD 4.3