A 2-opt tour move removes two boundary arcs and reverses the intervening block to reconnect one tour. Such moves define a local-search neighbourhood; block reversals of length two include adjacent swaps and hence connect permutation schedules. For directed costs the asymmetric 2-opt reversal cost must include every reversed internal arc, not just the boundary changes.
2-opt is a local search algorithm commonly used to optimize routes in the field of combinatorial optimization, particularly in solving the traveling salesman problem (TSP) and related routing problems. The basic idea of 2-opt is to improve a given tour (or route) by iteratively removing two edges and reconnecting the two segments in a way that results in a shorter total distance.
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