bessi0.c

来自「适合大型数值计算代码 现在网络上已经找不到了 购买需要20$」· C语言 代码 · 共 23 行

#include <math.h>

float bessi0(float x)
{
	float ax,ans;
	double y;

	if ((ax=fabs(x)) < 3.75) {
		y=x/3.75;
		y*=y;
		ans=1.0+y*(3.5156229+y*(3.0899424+y*(1.2067492
			+y*(0.2659732+y*(0.360768e-1+y*0.45813e-2)))));
	} else {
		y=3.75/ax;
		ans=(exp(ax)/sqrt(ax))*(0.39894228+y*(0.1328592e-1
			+y*(0.225319e-2+y*(-0.157565e-2+y*(0.916281e-2
			+y*(-0.2057706e-1+y*(0.2635537e-1+y*(-0.1647633e-1
			+y*0.392377e-2))))))));
	}
	return ans;
}