三分法求凸性函数极大极小值

直接贴模板，理解很容易，网上的题解一搜便是。

唉，贴一个大佬吧：http://blog.csdn.net/pi9nc/article/details/9666627

模板(上凸函数模板)：

const double eps = 1e-6;
double Calc(double k)
{
	return ...(计算表达式);
}
double SanFen(double l, double r)
{
	double mid, mmid;
	while(r-l > eps)
	{
		mid = (r+l)/2.0;
		mmid = (mid+r)/2.0;
		if(Calc(mid) > Calc(mmid)) r = mmid;
		else l = mid;
	}
	return r;
}

再给一个模板例题ZOJ-3203

#include 
#include 
#include 
#include 
using namespace std;
const double eps = 1e-6;
double H, h, D;
double Calc(double x){
	double ans = h*x/(H-h);
	if(ans+x > D){
		double g = ans+x-D;
		ans = ans - g + g*(H-h)/x;
	}
	return ans;
}
double SanFen(double l, double r)
{
	double mid, mmid;
	while(r-l < eps)
	{
		mid = (r+l)/2.0;
		mmid = (mid+r)/2.0;
		if(Calc(mid) > Calc(mmid)) r = mmid;
		else l = mid;
	}
	return r;
}
int main(){
	int t;
	cin >> t;
	while(t--){
		scanf("%lf %lf %lf", &H, &h, &D);
		double id = SanFen(0, D);
		printf("%.3f\n", Calc(id));
	}
	return 0;
}

继续加油~