Elsevier

Applied Mathematics and Computation

Volume 222, 1 October 2013, Pages 94-106
Applied Mathematics and Computation

An improved global-best harmony search algorithm

https://doi.org/10.1016/j.amc.2013.07.020Get rights and content

Abstract

This paper introduces an improved global-best harmony search (IGHS) algorithm. The proposed modifications effectively combines a novel improvisation scheme with a previously developed mechanism for updating the pitch adjustment rate (PAR) and the distance bandwidth (bw). The aim of this modification is to efficiently investigate the search space by going through the stages of exploration and exploitation. The proposed algorithm is compared against seven previous modifications to HS using rigorous statistical tests when applied to the CEC05 benchmark functions showing a superior performance on most of the tested functions.

Introduction

Harmony search (HS) [6], [16] is a relatively new optimization algorithm that has been proposed in the last decade. The main idea behind the algorithm is to simulate the behavior of a musician looking for the right harmony. Among the many benefits of HS [6] is having a few and relatively easy mathematical equations as well as considering all the members of the current population while producing a new harmony.

The main drawback of HS is the failure to fine tune the final solution towards the end of the search [7]. Many attempts have been pursued to overcome this disadvantage and improve the performance of HS. The authors in [7] introduced the improved HS by proposing new technique for adjusting the algorithm parameters during the search. Ideas borrowed from swarm intelligence have been also utilized in the global-best HS [10]. Differential evolution operators have been incorporated into HS in [4]. Finally, two adaptive versions of HS have been recently proposed in [15], [12].

In this paper, we introduce an improved version of the global-best HS by proposing a new harmony improvisation scheme that is effectively combined with a mechanism for adjusting the algorithm parameters. The main reason for this modification is to control the algorithm search strategy and allow it to gradually shift from the exploration behavior at the beginning of the search to the exploitation behavior at the end. Our algorithm is compared against all other previously introduced HS algorithms when applied to a well-known benchmark library.

Section 2 gives an introduction to HS. All previously proposed improvements for HS are covered in Section 3. Our proposed algorithm is presented in Section 4. Section 5 presents the experimental results. Finally, the paper is concluded in Section 6.

Section snippets

Harmony search

HS [6], [16] was introduced as an imitation of the musical process that searches for a harmony balance. In HS, each variable of the problem is regarded as the pitch of a different musical instrument and the complete solution is referred to as a harmony vector. If the pitch (decision variable value) makes good harmony (good objective function value), it is stored in memory.

The memory part is modeled using a memory structure referred to as the Harmony Memory (HM). Initially, HS is initialized

Previous improvements

The overview presented in [8] covered most of the previous improvements introduced into HS. These improvements were categorized into improvements in terms of parameter settings or in terms of hybridization with other meta-heuristic algorithms. According to this classification, the variants tested in this work fall in the first category.

Improved global-best harmony search

In this work, we introduce a new improved global-best harmony search (IGHS) algorithm. We believe that a lot of successful improvements were introduced in HS. However, these improvements could be mixed more efficiently to have a better performance.

The basic idea is that we need to have an explorative performance at the beginning of the search while having an exploiting one towards the end. The explorative behavior is realized by searching around randomly selected harmonies from memory with

Experimental procedure

HS, HSPop, DHS, GHS, IHS, AHS, SGHS and IGHS are all applied to the CEC05 benchmark functions [14] for problem sizes of D=10,D=30 and D=50. The algorithms are allowed to perform a maximum of 104×D function evaluations. Function f8 was excluded from the comparisons as it has the global optimum near the bounds and it acts as the needle-in-hay-stack problem. All algorithms applied to this function practically reach the same solution.

The MATLAB code for HS was obtained through private communication

Conclusions

This paper introduced an improved global-best harmony search (IGHS) algorithm. The algorithm exhibited the desirable behavior of exploring the search space at the beginning while moving towards exploiting good solutions near the end. This was achieved by searching a wide area around random solutions (using Gaussian distribution) while searching a small area around the best solution (using uniform distribution). The searching areas were made smaller over time by exponentially decreasing bw and

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    Then, HS moves candidate solutions in the search space to find the optimal solution through application of some search operators that model the pitch selection and adjustment actions in production of right harmonies. Despite significant success of HS applications, several studies have pointed out that search mechanisms of HS exhibit excellent explorative behavior but poor exploitative ability [21,22]. This inefficiency is originated from the insufficient utilization of history information and experience gathered during search process in harmony memory (HM).

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