Iterated local search with ejection chains for the space-free multi-row facility layout problem

This paper presents an iterated local search algorithm based on ejection chains to solve the space-free multi-row facility layout problem. The aim of this problem is to find a non-overlapping layout of facilities on a given number of rows such that there is no space between two adjacent facilities. In addition, the left-most facility of the arrangement must have zero abscissa. Our algorithm looks for a local optimal solution by continuously alternating ejection moves and trial moves to form an ejection chain. Since the ejection chain can compound simple moves to create more complex and powerful moves, it has a greater chance to discover better solutions. Additionally, we propose a directional perturbation strategy to produce a solution of both high quality and good diversity. The idea is to calculate the score of each facility based on the location concentration of facilities in the elite solution set and the historical perturbation times of facilities in the search process, and to select the facility with the highest score for perturbation. Experimental results on four benchmark sets containing a total of 290 instances reveal that the proposed algorithm performs better for 131 (45.2%) instances in terms of best solution values and for 196 (80.0%) instances in terms of average solution values than a recently reported state-of-the-art algorithm.