hdu 2899

                                             Strange fuction

Problem Description

Now, here is a fuction:
F(x) = 6 * x^7+8*x^6+7*x^3+5*x^2-y*x (0 <= x <=100)
Can you find the minimum value when x is between 0 and 100.


Input
The first line of the input contains an integer T(1<=T<=100) which means the number of test cases. Then T lines follow, each line has only one real numbers Y.(0 < Y <1e10)


Output
Just the minimum value (accurate up to 4 decimal places),when x is between 0 and 100.


Sample Input

2
100
200



Sample Output

-74.4291

-178.8534

题意：求单峰函数F(x)的最小值，可以用三分来求，虽然是凸函数，同样可以求。

<span style="font-size:18px;">#include <iostream>#include<cstdio>#include<cmath>#define ESP 1e-5using namespace std;double y;double f(double x,double y){    return 6*pow(x,7)+8*pow(x,6)+7*pow(x,3)+5*pow(x,2)-y*x;}double SanFen(double l,double r)//求【l,r】之间的最小值{    double fmid,fmmid;    while(r-l>ESP)    {        double mid=(l+r)/2.0;        double mmid=(mid+r)/2.0;        fmid=f(mid,y);        fmmid=f(mmid,y);        if(fmid<fmmid)//因为是求最小值，当fmid<fmmid时，将r向l靠近            r=mmid;        else//否则，将l向r靠近            l=mid;    }    return fmid;}int main(){    int t;    scanf("%d",&t);    while(t--)    {        scanf("%lf",&y);        printf("%0.4lf\n",SanFen(0,100));    }    return 0;}</span>