co nd - m at / 9 90 20 34 2 Fe b 19 99 Combinatorial Optimization by Iterative Partial

A procedure is presented which considerably improves the performance of local search based heuristic algorithms for combinatorial optimization problems. It increases the average \gain" of the individual local searches by merging pairs of solutions: certain parts of either solution are transcribed by the related parts of the respective other solution, corresponding to ipping clusters of a spin glass. This iterative partial transcription acts as a local search in the subspace spanned by the diiering components of both solutions. Embedding it in the simple multi-start-local-search algorithm and in the thermal-cycling method, we demonstrate its eeectiveness for several instances of the travel-ing salesman problem. The obtained results indicate that, for this task, such approaches are far superior to simulated annealing.