代码 | 自适应大邻域搜索系列之(3) - Destroy和Repair方法代码实现解析

前言

上一篇文章中我们具体解剖了ALNS类的具体代码实现过程，不过也留下了很多大坑。接下来的文章基本都是“填坑”了，把各个模块一一展现解析给大家。不过碍于文章篇幅等原因呢，也不会每一行代码都进行讲解，那些简单的代码就跳过了，相信大家也能一眼就看懂。好了，废话不多说，开始干活吧。

01 照旧总体概述

前面我们提到，ALNS中的重中之重就是Destroy和Repair方法了，在整一个ALNS框架中呢，涉及这俩货的有Destroy和Repair方法的具体实现、Destroy和Repair方法管理（包括各个Destroy和Repair方法权重分配、成绩打分、按权重选择哪个Destroy和Repair方法等操作）。所以在这次的ALNS代码中呢，这俩货的代码实现呢也分为两个模块：

• Destroy和Repair方法具体实现模块
• Destroy和Repair方法管理模块

下面我们将对其进行一一讲解，不知道大家小板凳准备好了没有。

02 Destroy和Repair方法具体实现

关于Destroy和Repair方法，由三个类组成，分别是AOperator、ADestroyOperator、ARepairOperator。它们之间的继承派生关系如下：

下面对其一一讲解。

2.1 AOperator

这是一个基础父类，它抽象了Destroy和Repair方法共有的一些方法和特征（成绩、权重、名称等等），然后Destroy和Repair方法再各自继承于它，实现自己的功能模块。成员变量已经注释清楚了，关于protected的一个成员noise噪声模式会在后面讲到。其他的方法也很简单就不做多解释了。

class AOperator
{
private:
	//! Total number of calls during the process.
	size_t totalNumberOfCalls;

	//! Number of calls since the last evaluation.
	size_t nbCallsSinceLastEval;

	//! score of the operator.
	double score;

	//! weight of the operator.
	double weight;

	//! designation of the operator.
	std::string operatorName;

protected:
	//! Indicate if the operator is used in noise mode or not.
	bool noise;
public:

	//! Constructor.
	AOperator(std::string name){
		operatorName = name;
		init();
	}

	//! Destructor.
	virtual ~AOperator(){};

	//! Initialize the values of the numbers of calls.
	void init()
	{
		totalNumberOfCalls = 0;
		nbCallsSinceLastEval = 0;
		score = 0;
		weight = 1;
	}

	//! reset the number of calls since last eval.
	void resetNumberOfCalls()
	{
		nbCallsSinceLastEval = 0;
	}

	//! Simple getter.
	//! \return the total number of calls to the operator since
	//! the beginning of the optimization process.
	size_t getTotalNumberOfCalls(){return totalNumberOfCalls;};

	//! Simple getter.
	//! \return the number of calls to this operator since the last
	//! evaluation.
	size_t getNumberOfCallsSinceLastEvaluation(){return nbCallsSinceLastEval;};

	void increaseNumberOfCalls()
	{
		totalNumberOfCalls++;
		nbCallsSinceLastEval++;
	}

	//! Simple getter.
	double getScore() const
    {
        return score;
    }

	//! Simple getter.
    double getWeight() const
    {
        return weight;
    }

    //! resetter.
    void resetScore()
    {
        this->score = 0;
    }

    //! Simple setter.
	void setScore(double s)
	{
		this->score = s;
	}

    //! Simple setter.
    void setWeight(double weight)
    {
        this->weight = weight;
    }

    //! Simple getter.
    std::string getName(){return operatorName;};

    //! Set noise to true.
    void setNoise(){noise=true;};

    //! Set noise to false.
    void unsetNoise(){noise=false;};

};

2.2 ADestroyOperator

该类主要是继承于上面的AOperator类，然后再此基础上加上Destroy操作的具体实现。它是一个抽象类，需要在后续的应用中重写Destroy操作的方法。

class ADestroyOperator : public AOperator {
protected:
	//! The minimum destroy size used.
	size_t minimunDestroy;
	//! The maximum destroy size used.
	size_t maximumDestroy;

public:
	//! Constructor.
	//! \param mini the minimum destroy size.
	//! \param maxi the maximum destroy size.
	//! \param s the name of the destroy operator.
	ADestroyOperator(size_t mini, size_t maxi, std::string s) : AOperator(s)
	{
		minimunDestroy = mini;
		maximumDestroy = maxi;
	}

	//! Destructor.
	virtual ~ADestroyOperator(){};

	//! This function is the one called to destroy a solution.
	//! \param sol the solution to be destroyed.
	virtual void destroySolution(ISolution& sol)=0;
};

2.3 ARepairOperator

同理，也是由AOperator类派生出来并加上Repair自己的实现方法的类。也是一个抽象类，需要在后续的使用中重写Repair方法。

class ARepairOperator : public AOperator {

public:
	ARepairOperator(std::string s) : AOperator(s)
	{
	}

	virtual ~ARepairOperator(){};

	virtual void repairSolution(ISolution& sol)=0;
};

03 Destroy和Repair方法管理

对Destroy和Repair方法进行管理的由两个类来实现：AOperatorManager、OperatorManager。其中AOperatorManager是抽象类，只提供接口，OperatorManager继承于AOperatorManager。并对其接口进行实现。

3.1 AOperatorManager

该类抽象了OperatorManager的一些特征，只提供接口。因此成员函数都是纯虚函数。相关方法的说明已经注释在代码里面了。关于保护成员：stats用于保存算法迭代过程中的一些状态量，这个类后续也会讲解的。

class AOperatorManager
{
public:
	//! This method selects a destroy operator.
	//! \return a destroy operator.
	virtual ADestroyOperator& selectDestroyOperator()=0;

	//! This method selects a repair operator.
	//! \return a repair operator.
	virtual ARepairOperator& selectRepairOperator()=0;

	virtual void recomputeWeights()=0;

	//! Update the scores of the operators.
	virtual void updateScores(ADestroyOperator& des, ARepairOperator& rep, ALNS_Iteration_Status& status)=0;

	//! Indicate that the optimization process starts.
	virtual void startSignal()=0;

	//! Destroy the operators registered to this operator manager.
	virtual void end()=0;

    //! Simple setter.
	void setStatistics(Statistics* statistics){stats = statistics;};
protected:
	//! A pointer to the instance of the statistics module.
	Statistics* stats;
};

3.2 OperatorManager

该类在AOperatorManager基础上也添加了一些自己额外的成员变量和函数方法。具体还是看代码理解吧，挺简单的，没有需要多解释的，我在这多少无益。

class OperatorManager: public AOperatorManager {
private:
	//! The set of repair operators.
	std::vector<AOperator*> repairOperators;

	//! The set of destroy operators.
	std::vector<AOperator*> destroyOperators;

	//! The sum of the weights of the repair operators.
	double sumWeightsRepair;

	//! The sum of the weights of the destroy operators.
	double sumWeightsDestroy;

	//! The paramaters to be used by the ALNS.
	ALNS_Parameters* parameters;

	//! Indicate whether or not the next operators to be return
	//! should be noised or not.
	bool noise;

	//! A counter that indicates the number of times repair operators with noise have been successfull
	double performanceRepairOperatorsWithNoise;
	//! A counter that indicates the number of times repair operators without noise have been successfull
	double performanceRepairOperatorsWithoutNoise;

	//! Use a roulette wheel to select an operator in a vector of operators.
	//! \return the selected operator.
	AOperator& selectOperator(std::vector<AOperator*>& vecOp, double sumW);

	//! Recompute the weight of an operator.
	void recomputeWeight(AOperator& op, double& sumW);
public:
	//! Constructor
	//! \param param the parameters to be used.
	OperatorManager(ALNS_Parameters& param);

	//! Destructor.
	virtual ~OperatorManager();

	//! This function recompute the weights of every operator managed by this
	//! manager.
	void recomputeWeights();

	//! This method selects a destroy operator.
	//! \return a destroy operator.
	ADestroyOperator& selectDestroyOperator();

	//! This method selects a repair operator.
	//! \return a repair operator.
	ARepairOperator& selectRepairOperator();

	//! This method adds a repair operator to the list
	//! of repair operator managed by this manager.
	//! \param repairOperator the repair operator to be added.
	void addRepairOperator(ARepairOperator& repairOperator);

	//! This method adds a destroy operator to the list
	//! of destroy operator managed by this manager.
	//! \param destroyOperator the destroy operator to be added.
	void addDestroyOperator(ADestroyOperator& destroyOperator);

	//! This method run some sanity checks to ensure that it is possible
	//! to "safely" use this manager within the ALNS.
	void sanityChecks();

	//! Update the scores of the operators.
	virtual void updateScores(ADestroyOperator& des, ARepairOperator& rep, ALNS_Iteration_Status& status);

	//! Indicate that the optimization process starts.
	virtual void startSignal();

	//! Destroy all the operators registered to this operator.
	void end();
};

上面是该类的.h文件，关于其中某些函数方法的实现，小编下面挑一些来重点给大家讲讲，那些以小编的脑瓜子都能理解的代码就省略了，大家应该都能懂……

3.3 OperatorManager具体实现

又到了一大波代码时间，来吧来吧，小板凳准备好，要开始啦~

3.3.1 OperatorManager::recomputeWeight(...)

重新计算单个操作的权重。其有两个参数AOperator& op, double& sumW，其中 op是要重新计算权重的repair或者destroy方法，sumW是其对应集合的权重总和。

这里只讲一个新权重的计算方式就行：



其中：

Rho为设定的[0, 1]之间的参数，PrevWeight表示旧的权重，nbCalls表示在上一次自上一次更新完权重到现在该方法被调用的次数，timeSegmentsIt表示迭代多少次需要重新计算一下权重的迭代次数，currentScore表示旧的成绩。理解了这些就很easy了。

void OperatorManager::recomputeWeight(AOperator& op, double& sumW)
{
	double prevWeight = op.getWeight();
	sumW -= prevWeight;
	double currentScore = op.getScore();
	size_t nbCalls = op.getNumberOfCallsSinceLastEvaluation();
	double newWeight = (1-parameters->getRho())*prevWeight + parameters->getRho()*(static_cast<double>(nbCalls)/static_cast<double>(parameters->getTimeSegmentsIt()))*currentScore;
	// We ensure that the weight is within the bounds.
	if(newWeight > parameters->getMaximumWeight())
	{
		newWeight = parameters->getMaximumWeight();
	}
	if(newWeight < parameters->getMinimumWeight())
	{
		newWeight = parameters->getMinimumWeight();
	}

	sumW += newWeight;
	op.setWeight(newWeight);
	op.resetScore();
	op.resetNumberOfCalls();
}

值得注意的是还有一个OperatorManager::recomputeWeights()成员函数是用于重新计算repair或者destroy方法集合的，它的实现主要也还是调用OperatorManager::recomputeWeight(AOperator& op, double& sumW)方法来实现的。

3.3.2 OperatorManager::selectOperator(...)

相信了解过遗传算法轮盘赌实现过程的小伙伴对这里都不会陌生，当然，并不是说权重大的方法一定会被选中，只是被选中的可能性会大而已。具体过程是先生成一个在0到sumWeight之间的中间权重randomWeightPos ，然后从第一个方法开始用变量cumulSum进行权重累加，直到cumulSum>=randomWeightPos 为止，那么停止累加时最后这个方法就是幸运儿了。

AOperator& OperatorManager::selectOperator(std::vector<AOperator*>& vecOp, double sumW)
{
	double randomVal = static_cast<double>(rand())/static_cast<double>(RAND_MAX);
	double randomWeightPos = randomVal*sumW;
	double cumulSum = 0;
	for(size_t i = 0; i < vecOp.size(); i++)
	{
		cumulSum += vecOp[i]->getWeight();
		if(cumulSum >= randomWeightPos)
		{
			if(noise)
			{
				vecOp[i]->setNoise();
			}
			else
			{
				vecOp[i]->unsetNoise();
			}
			vecOp[i]->increaseNumberOfCalls();
			return *(vecOp[i]);
		}
	}
	assert(false);
	return *(vecOp.back());
}

3.3.3 OperatorManager::updateScores(...)

该成员函数用来更新各个Destroy和Repair方法的成绩。参数是Destroy和Repair方法的集合，以及ALNS迭代过程中的各种状态信息。便于说明下面用rScore和dScore分别代表Repair和Destroy方法的成绩。具体实现如下：

1. 如果找到新的最优解，rScore+=Sigma1，dScore+=Sigma1。其中Sigma1是设定参数。
2. 如果当前解得到改进，rScore+=Sigma2，dScore+=Sigma2。其中Sigma2是设定参数。
3. 如果当前解没有得到改进 and 当前解是之前没有出现过的 and 当前解被接受作为新的解了，rScore+=Sigma3，dScore+=Sigma3。其中Sigma3是设定参数。

void OperatorManager::updateScores(ADestroyOperator& des, ARepairOperator& rep, ALNS_Iteration_Status& status)
{
	if(status.getNewBestSolution() == ALNS_Iteration_Status::TRUE)
	{
		rep.setScore(rep.getScore()+parameters->getSigma1());
		des.setScore(des.getScore()+parameters->getSigma1());
		performanceRepairOperatorsWithNoise += 1;
		performanceRepairOperatorsWithoutNoise += 1;
	}

	if(status.getImproveCurrentSolution() == ALNS_Iteration_Status::TRUE)
	{
		rep.setScore(rep.getScore()+parameters->getSigma2());
		des.setScore(des.getScore()+parameters->getSigma2());
		performanceRepairOperatorsWithNoise += 1;
		performanceRepairOperatorsWithoutNoise += 1;
	}

	if(status.getImproveCurrentSolution() == ALNS_Iteration_Status::FALSE
			&& status.getAcceptedAsCurrentSolution() == ALNS_Iteration_Status::TRUE
			&& status.getAlreadyKnownSolution() == ALNS_Iteration_Status::FALSE)
	{
		rep.setScore(rep.getScore()+parameters->getSigma3());
		des.setScore(des.getScore()+parameters->getSigma3());
		performanceRepairOperatorsWithNoise += 1;
		performanceRepairOperatorsWithoutNoise += 1;
	}
	/* OLD VERSION */
	/*
	if(parameters->getNoise())
	{
		double randNoise = static_cast<double>(rand())/RAND_MAX;
		noise = (randNoise<parameters->getProbabilityOfNoise());
	}
	*/
	/* NEW VERSION */

	if(parameters->getNoise())
	{
		double performanceRepairOperatorsGlobal = 0;
		performanceRepairOperatorsGlobal += performanceRepairOperatorsWithNoise;
		performanceRepairOperatorsGlobal += performanceRepairOperatorsWithoutNoise;

		double randomVal = static_cast<double>(rand())/RAND_MAX;
		double randomWeightPos = randomVal*performanceRepairOperatorsGlobal;
		noise = (randomWeightPos < performanceRepairOperatorsGlobal);
	}
}

至此，差不过难点都讲完了，不知道你萌都understand了吗？

04 小结

好了，以上就是今天的代码内容，别急着走开哦，后面还有好多好多的内容没讲呢。

这是个天坑，希望大家和小编一起努力，共同填完它。哈哈，谢谢各位的至此。