Two-level modified simulated annealing based approach for solving facility layout problem

In this paper, we are considering the quadratic assignment model (QAP) of the facility layout problem (FLP) which is known to be NP-hard. We relax the integer constraints of the QAP and solve it on a commercially available package called LINGO 8. In the optimal solution so obtained, Xijs take real values between zero and one. We identify promising Xijs having a value strictly greater than 0.5 in the optimal solution and set them to one. We add the constraints (Xij = 1) associated with promising Xijs into the QAP (with integer restrictions) and resolve using LINGO 8. In all the cases attempted we obtained a superior feasible solution to the QAP which was further improved by the proposed modified simulated annealing (MSA) procedure. An encouraging comparative performance of this procedure is thus reported.