代码 | 自适应大邻域搜索系列之(2) - ALNS算法主逻辑结构解析

//!   当前解。
ISolution* currentSolution;

//! 判断接受准则。
IAcceptanceModule* acceptanceCriterion;

//! ALNS算法运行的相关参数。
ALNS_Parameters* param;

//! destroy和repair方法的管理者。
AOperatorManager* opManager;

//! 最优解的管理者。
IBestSolutionManager* bestSolManager;

//! 局部搜索的管理者。
ILocalSearchManager* lsManager;

//! 自上次重新计算重新的权重以来的迭代次数。
size_t nbIterationsWC;

//! 当前迭代次数。
size_t nbIterations;

//! The current number of iterations without improvement.
size_t nbIterationsWithoutImprovement;

//! The number of iterations without improvement of the current solution.
size_t nbIterationsWithoutImprovementCurrent;

//! The number of iterations without acceptation of a transition.
size_t nbIterationsWithoutTransition;

//! The number of iterations since the last call to a local search
//! operator.
size_t nbIterationsWithoutLocalSearch;

//! 求解的总时间。
clock_t startingTime;

//! 最优解的下界。
double lowerBound;

//! A set containing the hash keys of the encountred solutions.
std::set<long long> knownKeys;

//! 用于计算求解过程的一些状态量。
Statistics stats;

//! 最近一次迭代的状态。
ALNS_Iteration_Status status;

//! 每次迭代完成后需要更新的对象。
std::vector<IUpdatable*> updatableStructures;

//! ALNS实例的名字。
std::string name;

//! Constructor.
//! \param name the name of the instance.
//! \param initialSolution the starting solution that is going to be optimized.
//! \param acceptanceCrit the module that determine whether or not a new solution
//! is accepted as the current solution.
//! \param parameters the set of parameters to be use by the ALNS.
//! \param opMan an operator manager.
ALNS(std::string instanceName,
	ISolution& initialSolution,
	IAcceptanceModule& acceptanceCrit,
	 ALNS_Parameters& parameters,
	 AOperatorManager& opMan,
	 IBestSolutionManager& solMan,
	 ILocalSearchManager& lsMan);

//! Destructor.
virtual ~ALNS();

//! This method launch the solving process.
//! \return true if a feasible solution is found,
//! false otherwise.
bool solve();

//! This method seeks if a solution is already known,
//! if not it is added to the set of known solutions.
//! \param sol the solution to be checked.
//! \return true if the solution was unknown, false otherwise.
bool checkAgainstKnownSolution(ISolution& sol);

//! This method perform one iteration of the ALNS solving
//! process.
void performOneIteration();

//! This method check whether or not the stopping criteria is met.
bool isStoppingCriterionMet();

//! Determine whether or not the new solution is better than the
//! best known solution.
bool isNewBest(ISolution* newSol);

//! \return the number of known solutions.
size_t getNumberKnownSolutions(){return knownKeys.size();};

//! Determine whether or not the new solution should be accepted
//! as the current solution.
bool transitionCurrentSolution(ISolution* newSol);

//! Return a pointer to the best known solution.
IBestSolutionManager* getBestSolutionManager(){return bestSolManager;};

//! Add an object to the list of object to be updated at the end of each
//! iteration of the ALNS.
//! \param up the updatable object to be added.
void addUpdatable(IUpdatable& up){updatableStructures.push_back(&up);};

//! Destroy the manager that have been provided at the construction of
//! the instance.
void end();

//构造
ALNS::ALNS(string instanceName,
		 ISolution& initialSolution,
		 IAcceptanceModule& acceptanceCrit,
		 ALNS_Parameters& parameters,
		 AOperatorManager& opMan,
		 IBestSolutionManager& bestSolMan,
		 ILocalSearchManager& lsMan)
{
	name = instanceName;
	currentSolution = initialSolution.getCopy();
	acceptanceCriterion = &acceptanceCrit;
	param = &parameters;
	lowerBound = -DBL_MAX;
	nbIterationsWC = 0;
	nbIterations = 0;
	nbIterationsWithoutImprovement = 0;
	opManager = &opMan;
	bestSolManager = &bestSolMan;
	lsManager = &lsMan;

	opManager->setStatistics(&stats);

	// We add the initial solution in the best solution manager.
	bestSolManager->isNewBestSolution(initialSolution);

	nbIterationsWithoutImprovementCurrent = 0;

	nbIterationsWithoutTransition = 0;

	nbIterationsWithoutLocalSearch = 0;
}
//析构
ALNS::~ALNS()
{
	delete currentSolution;
}

void ALNS::performOneIteration()
{
    //重新初始化一些状态量。
	status.partialReinit();
    //选择Repair和Destroy方法
	ARepairOperator& repair = opManager->selectRepairOperator();
	ADestroyOperator& destroy = opManager->selectDestroyOperator();

	ISolution* newSolution = currentSolution->getCopy();
    //输出迭代次数等信息。 param->getLogFrequency()获取的是logFrequency变量的值，logFrequency变量表示的意思是每隔多少次输出一下相关信息。
	if(nbIterations % param->getLogFrequency() == 0)
	{
		cout << "[ALNS] it. " << nbIterations << " best sol: " << (*(bestSolManager->begin()))->getObjectiveValue() << " nb known solutions: " << knownKeys.size() << endl;
	}
    //destroy操作
	destroy.destroySolution(*newSolution);
    //更新状态
	status.setAlreadyDestroyed(ALNS_Iteration_Status::TRUE);
	status.setAlreadyRepaired(ALNS_Iteration_Status::FALSE);//未进行repair操作
    //表示newSolution还是status的信息对解进行更新。这里只提供接口，后面应用的时候要具体重写。
	for(vector<IUpdatable*>::iterator it = updatableStructures.begin(); it != updatableStructures.end(); it++)
	{
		(*it)->update(*newSolution,status);
	}
    //进行repair操作
	repair.repairSolution(*newSolution);
	status.setAlreadyRepaired(ALNS_Iteration_Status::TRUE);
    //更新迭代次数
	nbIterations++;
	status.setIterationId(nbIterations);
	nbIterationsWC++;

	double newCost = newSolution->getObjectiveValue();
    //判断新生产的解是不是新的最优解
	isNewBest(newSolution);
    //判断新生成的解之前有没有出现过
	checkAgainstKnownSolution(*newSolution);
    //判断新生成的解和当前解谁更优
	bool betterThanCurrent = (*newSolution)<(*currentSolution);
    //如果新生成的解更优
	if(betterThanCurrent)
	{
		nbIterationsWithoutImprovementCurrent = 0;//清0
		status.setImproveCurrentSolution(ALNS_Iteration_Status::TRUE);
	}
    //否则
	else
	{
		nbIterationsWithoutImprovementCurrent++;
		status.setImproveCurrentSolution(ALNS_Iteration_Status::FALSE);//解没有得到提高
	}
    //更新状态
	status.setNbIterationWithoutImprovementCurrent(nbIterationsWithoutImprovementCurrent);
    //param->getPerformLocalSearch()指出要不要用LocalSearch，然后再用LocalSearch对新生成的解进行搜索。lsManager->useLocalSearch(*newSolution,status)将返回true如果经过LocalSearch之后的解有改进的话。
	if(param->getPerformLocalSearch() && lsManager->useLocalSearch(*newSolution,status))
	{
    //判断LocalSearch之后的新解是不是最优解。
		bestSolManager->isNewBestSolution(*newSolution);
	}
    //判断是否接受当前的解。
	bool transitionAccepted = transitionCurrentSolution(newSolution);
    //如果接受
	if(transitionAccepted)
	{
		status.setAcceptedAsCurrentSolution(ALNS_Iteration_Status::TRUE);
		nbIterationsWithoutTransition = 0;
	}
    //否则
	else
	{
		status.setAcceptedAsCurrentSolution(ALNS_Iteration_Status::FALSE);
		nbIterationsWithoutTransition++;
	}
    //更新信息
	status.setNbIterationWithoutTransition(nbIterationsWithoutTransition);
    //再一次进行LocalSearch操作，以取得更好的效果。
	if(param->getPerformLocalSearch() && lsManager->useLocalSearch(*newSolution,status))
	{
		bestSolManager->isNewBestSolution(*newSolution);
		if(status.getAcceptedAsCurrentSolution() == ALNS_Iteration_Status::TRUE)
		{
			transitionCurrentSolution(newSolution);
		}
	}
    //对destroy,repair方法进行成绩更新。
	opManager->updateScores(destroy,repair,status);

    //记录本次迭代过程的一些信息。
	stats.addEntry(static_cast<double>(clock()-startingTime)/CLOCKS_PER_SEC,nbIterations,destroy.getName(),repair.getName(),newCost,currentSolution->getObjectiveValue(),(*(bestSolManager->begin()))->getObjectiveValue(),knownKeys.size());

    //更新destroy,repair方法的权重。是在进行了一定迭代次数以后才更新的，具体次数由param->getTimeSegmentsIt()获得。
	if(nbIterationsWC % param->getTimeSegmentsIt() == 0)
	{
		opManager->recomputeWeights();
		nbIterationsWC = 0;
	}
    //接口，对解的某些部分再次更新。
	for(vector<IUpdatable*>::iterator it = updatableStructures.begin(); it != updatableStructures.end(); it++)
	{
		(*it)->update(*newSolution,status);
	}
    //如果有需要，将当前解转变成最优解再进行下一次迭代操作。
	currentSolution = bestSolManager->reloadBestSolution(currentSolution,status);

	delete newSolution;
}

bool ALNS::checkAgainstKnownSolution(ISolution& sol)
{
	bool notKnownSolution = false;
	long long keySol = sol.getHash();
    //哈希值匹配
	if(knownKeys.find(keySol) == knownKeys.end())
	{
		notKnownSolution = true;
		knownKeys.insert(keySol);
	}
    //之前已经出现过的解。
	if(!notKnownSolution)
	{
		status.setAlreadyKnownSolution(ALNS_Iteration_Status::TRUE);
	}
    //全新的解，之前没有出现过。
	else
	{
		status.setAlreadyKnownSolution(ALNS_Iteration_Status::FALSE);
	}
	return notKnownSolution;
}

bool ALNS::isNewBest(ISolution* newSol)
{
    //如果是新的最优解
	if(bestSolManager->isNewBestSolution(*newSol))
	{
		status.setNewBestSolution(ALNS_Iteration_Status::TRUE);
		nbIterationsWithoutImprovement = 0;
		status.setNbIterationWithoutImprovement(nbIterationsWithoutImprovement);
		status.setNbIterationWithoutImprovementSinceLastReload(0);
		return true;
	}
    //如果不是。
	else
	{
		status.setNewBestSolution(ALNS_Iteration_Status::FALSE);
		nbIterationsWithoutImprovement++;
		status.setNbIterationWithoutImprovement(nbIterationsWithoutImprovement);
		status.setNbIterationWithoutImprovementSinceLastReload(status.getNbIterationWithoutImprovementSinceLastReload()+1);
		return false;
	}
}

bool ALNS::transitionCurrentSolution(ISolution* newSol)
{
    //如果接受。
	if(acceptanceCriterion->transitionAccepted(*bestSolManager,*currentSolution,*newSol,status))
	{
		delete currentSolution;
		currentSolution = newSol->getCopy();
		return true;
	}
    //不接受，原来解不变，什么也不做。
	else
	{
		return false;
	}
}

bool ALNS::isStoppingCriterionMet()
{
    //是否找到最优可行解。
	if((*(bestSolManager->begin()))->isFeasible() && (*(bestSolManager->begin()))->getObjectiveValue() == lowerBound)
	{
		return true;
	}
	else
	{
		switch(param->getStopCrit())
		{
            //是否达到最大迭代次数。
			case ALNS_Parameters::MAX_IT: {
				return nbIterations >= param->getMaxNbIterations();
			}
            //是否达到最大限制运行时间。
			case ALNS_Parameters::MAX_RT: {
				clock_t currentTime = clock();
				double elapsed = (static_cast<double>(currentTime - startingTime)) / CLOCKS_PER_SEC;
				return elapsed >= param->getMaxRunningTime();
			}
            //the maximum number of iterations without improvement. 
			case ALNS_Parameters::MAX_IT_NO_IMP: {
				return nbIterationsWithoutImprovement >= param->getMaxNbIterationsNoImp();
			}
           //a mix of the MAX_IT, MAX_RT and MAX_IT_NO_IMP.
			case ALNS_Parameters::ALL: {
				if(nbIterations >= param->getMaxNbIterations())
				{
					return true;
				}
				if(nbIterationsWithoutImprovement >= param->getMaxNbIterationsNoImp())
				{
					return true;
				}
				clock_t currentTime = clock();
				double elapsed = (static_cast<double>(currentTime - startingTime)) / CLOCKS_PER_SEC;
				if(elapsed >= param->getMaxRunningTime())
				{
					return true;
				}
				return false;
			}

			default: {
				assert(false);
				return false;
			}
		}
	}

}

bool ALNS::solve()
{
	startingTime = clock();
	param->setLock();
	acceptanceCriterion->startSignal();
	opManager->startSignal();
	stats.setStart();
    //如果没有遇到终止条件，那么将一次次迭代下去。
	while(!isStoppingCriterionMet())
	{
		performOneIteration();
	}
    //获取运行结果，返回解是否可行。
	string pathGlob = param->getStatsGlobPath();
	pathGlob += name;
	pathGlob += ".txt";
	string pathOp = param->getStatsOpPath();
	pathOp += name;
	pathOp += ".txt";
	stats.generateStatsFile(pathGlob,pathOp);
	return (*(bestSolManager->begin()))->isFeasible();
}