黄金比分割の三分探索 (algorithm/ternary_search.cpp)
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- Last commit date: 2020-04-29 14:28:04+09:00
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#ifndef H_ternary_search
#define H_ternary_search
/**
* @brief 黄金比分割の三分探索
* @author えびちゃん
*/
#include <cmath>
#include <utility>
template <typename Fn, typename Tp>
auto optimize_convex(Fn&& f, Tp xl, Tp xu, Tp err, bool maximize = true) {
// Return {argmax f(x), max f(x)} if maximize, {argmin f(x), min f(x)}
// otherwise. If f is not convex in [xl, xu], the behavior is undefined.
Tp const phi = (1 + std::sqrt(static_cast<Tp>(5))) / 2;
int const iter = (std::log(xu-xl) - std::log(err)) / std::log(phi) + 1;
Tp xml = (phi * xl + xu) / (1 + phi);
Tp xmu = (xl + phi * xu) / (1 + phi);
Tp yml = f(xml);
Tp ymu = f(xmu);
for (int i = 0; i < iter; ++i) {
if (!maximize ^ (yml > ymu)) {
xu = xmu;
xmu = xml;
ymu = yml;
xml = (phi * xl + xu) / (1 + phi);
yml = f(xml);
} else {
xl = xml;
xml = xmu;
yml = ymu;
xmu = (xl + phi * xu) / (1 + phi);
ymu = f(xmu);
}
}
return std::make_pair(xml, yml);
}
#endif /* !defined(H_ternary_search) */
#line 1 "algorithm/ternary_search.cpp"
/**
* @brief 黄金比分割の三分探索
* @author えびちゃん
*/
#include <cmath>
#include <utility>
template <typename Fn, typename Tp>
auto optimize_convex(Fn&& f, Tp xl, Tp xu, Tp err, bool maximize = true) {
// Return {argmax f(x), max f(x)} if maximize, {argmin f(x), min f(x)}
// otherwise. If f is not convex in [xl, xu], the behavior is undefined.
Tp const phi = (1 + std::sqrt(static_cast<Tp>(5))) / 2;
int const iter = (std::log(xu-xl) - std::log(err)) / std::log(phi) + 1;
Tp xml = (phi * xl + xu) / (1 + phi);
Tp xmu = (xl + phi * xu) / (1 + phi);
Tp yml = f(xml);
Tp ymu = f(xmu);
for (int i = 0; i < iter; ++i) {
if (!maximize ^ (yml > ymu)) {
xu = xmu;
xmu = xml;
ymu = yml;
xml = (phi * xl + xu) / (1 + phi);
yml = f(xml);
} else {
xl = xml;
xml = xmu;
yml = ymu;
xmu = (xl + phi * xu) / (1 + phi);
ymu = f(xmu);
}
}
return std::make_pair(xml, yml);
}