论文标题

频繁更改的前导者快速重新挑选

Fast Re-Optimization of LeadingOnes with Frequent Changes

论文作者

Bulanova, Nina, Buzdalova, Arina, Doerr, Carola

论文摘要

在实际优化方案中,要求我们解决的问题实例可能会在优化过程中发生变化,例如,当可用新信息或环境条件发生变化时。在这种情况下,人们可以希望通过从最佳解决方案的最佳解决方案继续进行搜索来实现合理的绩效。同样,人们可能希望,在解决彼此相似的几个问题实例时,``温暖启动''第二个实例的优化过程是通过第一个实例的最佳解决方案的优化过程。但是,在[Doerr等,Gecco 2019]中表明,即使使用结构良好的溶液初始化,进化算法也可能具有通过结构上更糟糕的溶液替换这些良好溶液的趋势,从而导致优化时间与相同算法没有优化的时间从scratch开始。 Doerr等人。还提出了一种克服这个问题的多样性机制。他们的方法平衡了围绕当前问题的最佳解决方案的贪婪搜索,并在上一个实例的最佳发现解决方案周围进行了搜索。 在这项工作中,我们首先表明Doerr等人建议的重新优化方法。当问题实例容易发生更频繁的更改时,达到限制。更确切地说,我们证明它们被陷入了动态领导者问题,而目标字符串会定期更改。然后,我们提出了对其算法的修改,该算法在围绕先前最好的解决方案和当前最佳解决方案之间进行了插值。我们从经验上评估了具有各种变化频率和不同扰动因子的Leadings实例上的平滑复选算法,并表明它表现出优于完全重新启动的(1+1)进化算法和Doerr等人的重新挑选方法。

In real-world optimization scenarios, the problem instance that we are asked to solve may change during the optimization process, e.g., when new information becomes available or when the environmental conditions change. In such situations, one could hope to achieve reasonable performance by continuing the search from the best solution found for the original problem. Likewise, one may hope that when solving several problem instances that are similar to each other, it can be beneficial to ``warm-start'' the optimization process of the second instance by the best solution found for the first. However, it was shown in [Doerr et al., GECCO 2019] that even when initialized with structurally good solutions, evolutionary algorithms can have a tendency to replace these good solutions by structurally worse ones, resulting in optimization times that have no advantage over the same algorithms started from scratch. Doerr et al. also proposed a diversity mechanism to overcome this problem. Their approach balances greedy search around a best-so-far solution for the current problem with search in the neighborhood around the best-found solution for the previous instance. In this work, we first show that the re-optimization approach suggested by Doerr et al. reaches a limit when the problem instances are prone to more frequent changes. More precisely, we show that they get stuck on the dynamic LeadingOnes problem in which the target string changes periodically. We then propose a modification of their algorithm which interpolates between greedy search around the previous-best and the current-best solution. We empirically evaluate our smoothed re-optimization algorithm on LeadingOnes instances with various frequencies of change and with different perturbation factors and show that it outperforms both a fully restarted (1+1) Evolutionary Algorithm and the re-optimization approach by Doerr et al.

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