A Mixed-coding Harmony Search Algorithm for the Closed Loop Layout Problem

Closed Loop Layout Problem (CLLP) is an NP-hard facility layout problem that determines the most favorable placement of facilities along a rectangle loop with adjustable size. The primary objective of the CLLP is to minimize the total transportation cost of the material flow between facilities. To obtain this objective, the optimal placement sequence of the facilities and the corresponding optimal size of the rectangle loop must be obtained at the same time. Although several metaheuristic-based methods have been proposed to tackle the CLLP, those methods only use metaheuristics to search the optimal placement sequence of facilities, and the optimal size of the rectangle loop is obtained by enumeration method. In order to improve the search efficiency of metaheuristics for the CLLP, this paper presents a Mixed-coding Harmony Search (MHS) algorithm which includes Permutation-based Discrete Harmony Search (PDHS) and Continuous Harmony Search (CHS). The PDHS part is designed to search the optimal placement sequence of facilities, and the CHS part is used to find the optimal size of the rectangle loop. Comparing experiments, which were conducted on 13 CLLP instances, have shown that the MHS algorithm obtains better results in less time than other existing metaheuristics.