代码 | 自适应大邻域搜索系列之(5)

前言

上一篇推文说了，后面的代码难度直线下降，各位小伙伴可以放去n的100次方心了。今天讲讲一些细枝末节，就是前面一直有提到的参数和一些状态的记录代码。这个简单啦，小编也不作过多解释了。大家直接看代码都能看懂，不过小编还是会把逻辑结构给大家梳理出来的。好了，开始干活。

01 ALNS_Iteration_Status

这个类，咳咳，不是抽象类了哈。主要用来记录ALNS迭代过程中的一些中间变量和状态等。主要是成员变量，成员函数都是简单的getter（获取成员变量的接口）或者setter（设置成员变量的接口）。所以这里就把成员变量贴出来好了，各个变量记录的内容注释也写得很详细，小编就不做多赘述以免扰乱了大家看代码的心。

private:

	//! Id of the iteration corresponding to this status.
	size_t iterationId;

	//! Number of iteration since the last improvement of the BKS
	size_t nbIterationWithoutImprovement;

	//! Number of iteration since the last improvement of the BKS
	//! or the last reload of the best known solution.
	size_t nbIterationWithoutImprovementSinceLastReload;

	//! Number of iterations since the last improvement of the current
	//! solution.
	size_t nbIterationWithoutImprovementCurrent;

	//! Number of iterations without transition.
	size_t nbIterationWithoutTransition;

	//! Indicate if a new best solution has been obtained.
	State newBestSolution;

	//! Indicate if the new solution has been accepted as the
	//! current solution.
	State acceptedAsCurrentSolution;

	//! Indicate if the new solution is already known.
	State alreadyKnownSolution;

	//! Indicate if the new solution improve the current solution.
	State improveCurrentSolution;

	//! Indicate if a local search operator has been used.
	State localSearchUsed;

	//! Indicate if solution has been improved by local search.
	State improveByLocalSearch;

	//! Indicate if the solution has already been repaired.
	State alreadyRepaired;

	//! Indicate if the new solution has already been destroyed.
	State alreadyDestroyed;

};

02 ALNS_Parameters

该类是ALNS运行过程中的一些参数设置，和上面的ALNS_Iteration_Status差不多，主要功能集中在成员变量上，成员函数都是简单的getter（获取成员变量的接口）或者setter（设置成员变量的接口）。照例把成员变量贴出来吧~

public:

	//! Enumeration representing the various kind of stopping criteria.
	//! MAX_IT: the maximum number of iterations.
	//! MAX_RT: the maximum run time.
	//! MAX_IT_NO_IMP: the maximum number of iterations without improvement.
	//! ALL: a mix of the MAX_IT, MAX_RT and MAX_IT_NO_IMP.
	enum StoppingCriteria {
		MAX_IT,
		MAX_RT,
		MAX_IT_NO_IMP,
		ALL
	};

	//! An enumeration listing a set of packaged AcceptanceModule Implementation.
	enum AcceptanceCriterioKind {
		SA
	};
protected:
	//! Maximum number of iterations performed by the ALNS.
	size_t maxNbIterations;

	//! Maximum running time of the ALNS.
	double maxRunningTime;

	//! Maximum number of iterations without any improvement.
	size_t maxNbIterationsNoImp;

	//! Which stopping criterion should be used.
	StoppingCriteria stopCrit;

	//! Indicate if noise should be used.
	bool noise;

	//! Indicate after how many iterations should the scores of
	//! the operators be recomputed.
	size_t timeSegmentsIt;

	//! Indicate the number of iterations that should be performed
	//! before reinitialization of the scores of the operators.
	size_t nbItBeforeReinit;

	//! score adjustment parameter in case the last remove-insert
	//! operation resulted in a new global best solution
	int sigma1;

	//! score adjustment parameter in case that the last remove-insert
	//! operation resulted in a solution that has not been accepted before and
	//! the objective value is better than the objective value of current solution
	int sigma2;

	//! score adjustment parameter in case that the last remove-insert
	//! operation resulted in a solution that has not been accepted before and such
	//! that the score objective value is worse than the one of current solution but
	//! the solution was accepted.
	int sigma3;

	//! reaction factor 0 <= rho <= 1 for the update of the weights of the
	//! operators.
	double rho;

	//! The minimum possible weight for an operator.
	double minimumWeight;

	//! The maximum possible weight for an operator.
	double maximumWeight;

	//! Indicates the probability of using noised operators.
	double probabilityOfNoise;

	//! Kind of acceptance criterion used.
	AcceptanceCriterioKind acKind;

	//! patht to the configuration file of the acceptance criterion.
	std::string acPath;

	//! path to the file where the global stats have to be saved.
	std::string statsGlobPath;

	//! path to the file where the operators stats have to be saved.
	std::string statsOpPath;

	//! Indicate every each iteration logging is done. 不懂看后面。
	int logFrequency;

	//! A set of forbidden operators. 不懂看后面。
	std::vector<std::string> forbidenOperators;

	//! A set of forbidden local search operators. 不懂看后面。
	std::vector<std::string> forbidenLsOperators;

	//! The minimum percentage of the solution destroyed by the destroy operators.
	int minDestroyPerc;

	//! The maximum percentage of the solution destroyed by the destroy operators.
	int maxDestroyPerc;

	//! Indicate after how many iterations without improvement
	//! does the best known solution is reloaded.
	size_t reloadFrequency;

	//! Indicate if local search should be used.
	bool performLocalSearch;

	//! When the optimization process start, the parameters
	//! should not be modified. lock is set to true when the
	//! optimization begin. If the setter of the value
	//! of one parameter is called while lock is true, an
	//! error is raised.
	bool lock;

};

不过有几个变量大家看了注释可能还不太明白是干嘛用的。在这里再解释一下。

logFrequency，隔多少次迭代输出一下当前的信息。直接给大家上两个图让大家心领神会一下：

1. logFrequency = 1
   

2. logFrequency = 100
   

懂了吧。

forbidenOperators是禁止的某些repair和destroy方法的集合，学过禁忌搜索的都知道这意味着什么，有些repair和destroy方法效果太差劲了，所以我们把它们给ban掉。

forbidenLsOperators和forbidenOperators差不多，不过它是禁止的某些LocalSearch方法的集合，效果太差嘛。。。

03 再论ALNS_Parameters

关于ALNS_Parameters它的大部分成员函数是简单的getter（获取成员变量的接口）或者setter（设置成员变量的接口）。但其CPP文件中，还有一个函数是从xml文件读取相应参数的。代码就不具体介绍了，主要是xml文件操作的一些api的使用，有现成的lib库，感兴趣的同学了解一下。

至于为什么用xml文件呢？其实直接把参数写死在程序里面也是可以的，不过读取xml文件获取相应的参数更符合标准，在实际生产中也更方便实用而已。

04 小结

至此，整一个ALNS模块已经讲得差不多了，不知道大家都看懂了没有。看不懂的话可以多看几遍，很多地方也只是小编个人的理解，不一定正确，如果你觉得你有更好的想法，也可以联系小编一起讨论。

后面再出多几篇估计就差不多了。把判断接受准则讲讲，把局部搜索讲讲就差不多可以了。最后谢谢大家一路过来的支持哈。

代码及相关内容可关注公众号。更多精彩尽在微信公众号【程序猿声】