三分
<pre><code>double f(double x){
//something
}
const double eps=1e-8;
double sanfen(double l, double r){
double mid,midr,ans;
while (fabs(r-l)>eps) {
mid=(l+r)/2;
midr=(mid+r)/2;
if(f(mid) < f(midr)) l=mid; else r=midr; //求最大值
}
ans=f(l);
return ans;
}</code></pre>