bessy1.c

Numerical Recipes 是国际公认的高水平的、关于数值计算的书

#include <math.h>

float bessy1(x)
float x;
{
	float z;
	double xx,y,ans,ans1,ans2;
	float bessj1();

	if (x < 8.0) {
		y=x*x;
		ans1=x*(-0.4900604943e13+y*(0.1275274390e13
			+y*(-0.5153438139e11+y*(0.7349264551e9
			+y*(-0.4237922726e7+y*0.8511937935e4)))));
		ans2=0.2499580570e14+y*(0.4244419664e12
			+y*(0.3733650367e10+y*(0.2245904002e8
			+y*(0.1020426050e6+y*(0.3549632885e3+y)))));
		ans=(ans1/ans2)+0.636619772*(bessj1(x)*log(x)-1.0/x);
	} else {
		z=8.0/x;
		y=z*z;
		xx=x-2.356194491;
		ans1=1.0+y*(0.183105e-2+y*(-0.3516396496e-4
			+y*(0.2457520174e-5+y*(-0.240337019e-6))));
		ans2=0.04687499995+y*(-0.2002690873e-3
			+y*(0.8449199096e-5+y*(-0.88228987e-6
			+y*0.105787412e-6)));
		ans=sqrt(0.636619772/x)*(sin(xx)*ans1+z*cos(xx)*ans2);
	}
	return ans;
}