hdu 1724 Ellipse——辛普森积分

题目：http://acm.hdu.edu.cn/showproblem.php?pid=1724

#include<cstdio>
#include<cstring>
#include<algorithm>
#include<cmath>
#define db double
using namespace std;
const db eps=1e-5;
int T;db a,b,l,r;
db f(db x){return sqrt((1-x*x/a)*b);}
db cal(db l,db r){return (f(l)+4*f((l+r)/2)+f(r))*(r-l)/6;}
db simp(db l,db r,db eps,db ret)
{db mid=(l+r)/2,vl=cal(l,mid),vr=cal(mid,r);if(fabs(vl+vr-ret)<=15*eps)return vl+vr+(vl+vr-ret)/15;//not ret+()/15return simp(l,mid,eps/2,vl)+simp(mid,r,eps/2,vr);
}
int main()
{scanf("%d",&T);while(T--){scanf("%lf%lf%lf%lf",&a,&b,&l,&r);a*=a;b*=b;printf("%.3lf\n",simp(l,r,eps,cal(l,r))*2);}return 0;
}