double angle4h(double v0[], double v1[]){
	double cos_theta = (dot4h(v0, v1)) / (length4h(v0)*length4h(v1));
	double theta;
	// theta = acos(cos_theta) * 180 / M_PI;
	theta = acos(cos_theta);

	#ifdef DEBUG
	printf("角度: %lf\n", theta);
	#endif
	return theta;
}
// ベクトル間の角度
double angle4h(double v0[], double v1[])
{
	double cos_theta = 0;
	double length_0 = length4h(v0);
	double length_1 = length4h(v1);
	if (length_0 != 0.0 && length_1 != 0.0)
	{
		cos_theta = dot4h(v0, v1) / (length_0 * length_1);
		return acos(cos_theta);
	}
	else
	{
		return 0;
	}
}