练习2.13 不用库函数，写一个高效计算ln N的C函数

代码

#include<stdio.h>  
double MYLOG(double a)  
{  
   int N = 15;  
   int k,nk;  
   double x,xx,y;  
   x = (a-1)/(a+1);  
   xx = x*x;  
   nk = 2*N+1;  
   y = 1.0/nk;  
   for(k=N;k>0;k--)  
   {  
     nk = nk - 2;  
     y = 1.0/nk+xx*y;  
   }  
   return 2.0*x*y;  
}  
  
int main()  
{ 
	int N=100;
	for(int a=1;a<N;a++)
		printf("ln %d = %.10f \n",a,MYLOG(a));
    getchar();  
    return 0;  
}