Optim Lett (2013) 7:407–413 DOI 10.1007/s11590-011-0426-8 ORIGINAL PAPER Optimal solutions for the double row layout problem André R. S. Amaral Received: 9 August 2011 / Accepted: 19 November 2011 / Published online: 30 November 2011 © Springer-Verlag 2011 Abstract The double row layout problem is how to allocate a given set of n machines on both sides of a straight line corridor so that the total cost of transporting materials between machines is minimized. This is a very difficult combinatorial optimization problem with important applications in industry. We formulate the problem as a mixed- integer program. Computational tests show that the proposed formulation presents a far superior performance than that of a previously published model. Keywords Double row layout problem · Machine layout problem · Facility layout · Integer programming 1 Introduction The double row layout problem (DRLP) is a very difficult combinatorial optimiza- tion problem. It occurs in automated manufacturing environments, where a material- handling device transports materials among machines arranged in a double-row layout, i.e. a layout in which the machines are located on both sides of a straight line corridor (see, for example, [15, 17]). An application of the DRLP within a fabrication line that produces liquid crystal display (LCD) was described by Chung and Tanchoco [8]. Facility layout problems are generally NP-hard, which means that their exact solu- tion within reasonable computer times is a very difficult task (e.g. for the two-dimen- sional facility layout problems considered by Sherali et al. [24], the largest instance size that could be solved to optimality has 9 machines). This work was carried out while the author was with CEG/IST - Instituto Superior Técnico, Portugal. A. R. S. Amaral (B ) Departamento de Informática, Universidade Federal do Espírito Santo (UFES), Vitória, ES 29060-900, Brazil e-mail: amaral@inf.ufes.br 123