凹函數求極小值,三分。
代碼如下:
#include <iostream>
#include <cstdio>
#include <cmath>
#include <cstdlib>
#include <cstring>
using namespace std;
double fx(double x, double y)
{
return 6*pow(x,7)+8*pow(x,6)+7*pow(x,3)+5*pow(x,2)-y*x;
}
int main()
{
#ifdef test
freopen("input.txt", "r", stdin);
#endif
int t;
double y;
scanf("%d", &t);
while(t--)
{
double l = 0, r = 100;
scanf("%lf", &y);
while(l + 1e-7<= r)
{
double mid = (l + r) / 2;
double midmid = (mid + r) / 2;
double ans_mid = fx(mid, y), ans_midmid = fx(midmid, y);
if(ans_mid <= ans_midmid)
r = midmid;
else
l = mid;
}
printf("%.4lf\n", fx((l+r)/2, y));
}
return 0;
}