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// Copyright 2008, 2009 Brady J. Garvin
// This file is part of Covering Arrays by Simulated Annealing (CASA).
// CASA is free software: you can redistribute it and/or modify it
// under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
// CASA is distributed in the hope that it will be useful, but
// WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU General Public License for more details.
// You should have received a copy of the GNU General Public License
// along with CASA. If not, see <http://www.gnu.org/licenses/>.
#ifndef ANNEALING_FILTER_H
#define ANNEALING_FILTER_H
#include <cassert>
#include <iostream>
#include "search/GreedyFilter.H"
#include "events/Listener.H"
// Decides, according to the rules of simulated annealing, when to take good
// moves and when to take bad ones.
// Should be added as a listener to search iterations in order that cooling be
// synchronized with the search.
template<class STATE, class COST>class AnnealingFilter :
public GreedyFilter<STATE,COST>,
public Listener<SearchIteration> {
typedef Heuristic<STATE,COST> HeuristicT;
typedef Goal<STATE> GoalT;
double temperature;
const double decay;
public:
AnnealingFilter(double temperature, double decay) :
temperature(temperature),
decay(decay) {
assert(0 <= decay);
assert(decay <= 1);
}
virtual ~AnnealingFilter() {}
void setTemperature(double temperature) {
this->temperature = temperature;
}
virtual double convertToDelta(COST childEstimate, COST parentEstimate) const
= 0;
void signal(const SearchIteration&message) {
temperature *= decay;
}
void operator()
(std::set<STATE>&children,
const STATE&parent,
const HeuristicT&heuristic,
const GoalT&goal) const {
GreedyFilter<STATE,COST>::operator()(children, heuristic, goal);
assert(children.size() <= 1);
if (children.size()) {
typename std::set<STATE>::iterator child = children.begin();
COST childEstimate = heuristic.estimate(*child, goal);
COST parentEstimate = heuristic.estimate(parent, goal);
if (!(parentEstimate < childEstimate)) {
// Always take good moves.
return;
}
double delta = convertToDelta(childEstimate, parentEstimate);
double probability = exp(delta / temperature);
int boundary = (int)(probability * RAND_MAX);
if (rand() < boundary) {
// Sometimes take bad moves.
return;
}
children.clear();
}
// When no moves are possible or a bad move is rejected, keep the parent.
children.insert(parent);
}
};
#endif
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