//解析几何+高斯迭代
#include <cstdio>
#include <cmath>
#define PI 3.141592653589793

class Point
{
	public:
		double x;
		double y;
};

Point p[4];
int iterfactor;
double x,y;

void setIterFactor(int num)
{
	iterfactor = num;
}

void setInitStatus(double a,double b)
{
	x = a;
	y = b;
}

int main()
{
	while(scanf("%lf %lf %lf %lf %lf %lf",
		&p[1].x,&p[1].y,&p[2].x,&p[2].y,&p[3].x,&p[3].y)!=EOF)
	{
		double a1,a2,c,b1,b2,d;
		a1 = p[3].x - p[1].x;
		a2 = p[3].y - p[1].y;
		c = (p[3].x + p[1].x) * a1 + (p[3].y + p[1].y) * a2;
		b1 = p[2].y - p[1].y;
		b2 = p[2].x - p[1].x;
		d = (p[2].y + p[1].y) * b1 + (p[2].x + p[1].x) * b2;

		if(a1==0&&b1==0)
		{
			y = (p[1].y + p[3].y) / 2.0;
			x = (p[1].x + p[2].x) / 2.0;
		}
		else if(a1==0)
		{
			a1 = p[3].x - p[2].x;
			a2 = p[3].y - p[2].y;
			c = (p[3].x + p[2].x) * a1 + (p[3].y + p[2].y) * a2;
			y = (p[1].y + p[3].y) / 2.0;
			x = (1.0 / (2.0 * a1)) * (c - 2.0 * a2 * y);
		}
		else if(b1==0)
		{
			b1 = p[2].y - p[3].y;
			b2 = p[2].x - p[3].x;
			d = (p[2].y + p[3].y) * b1 + (p[2].x + p[3].x) * b2;
			x = (p[1].x + p[2].x) / 2.0;
			y = (1.0 / (2.0 * b1)) * (d - 2.0 * b2 * x);
		}
		else
		{
			setIterFactor(11);
			setInitStatus(0,0);
			while(iterfactor--)
			{
				x = (1.0 / (2.0 * a1)) * (c - 2.0 * a2 * y);
				y = (1.0 / (2.0 * b1)) * (d - 2.0 * b2 * x);
			}
		}

		double L1_x = x - p[1].x;
		double L1_y = y - p[1].y;
		double r = sqrt(L1_x*L1_x+L1_y*L1_y);
		double circumference = 2 * PI * r;
		printf("%.2lf\n",circumference);
	}
}

会不会是有些输入的迭代矩阵用高斯迭代不收敛，求大神帮忙看看问题出在哪。。

• 高中几何知识即可求解。 (2) nero19960329 2016-07-09 16:51:02