代码 | 自适应大邻域搜索系列之(5) - ALNS_Iteration_Status和ALNS_Parameters的代码解析
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：
-
logFrequency = 1
-
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。
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