The traveling salesman problem on grids with forbidden neighborhoods


We introduce the traveling salesman problem with forbidden neighborhoods (TSPFN). This is an extension of the Euclidean TSP in the plane where direct connections between points that are too close are forbidden. The TSPFN is motivated by an application in laser beam melting. In the production of a workpiece in several layers using this method one hopes to reduce the internal stresses of the workpiece by excluding the heating of positions that are too close. The points in this application are often arranged in some regular (grid) structure. In this paper we study optimal solutions of TSPFN instances where the points in the Euclidean plane are the points of a regular grid. Indeed, we explicitly determine the optimal values for the TSPFN and its associated path version on rectangular regular grids for different minimal distances of the points visited consecutively. For establishing lower bounds on the optimal values we use combinatorial counting arguments depending on the parities of the grid dimensions. Furthermore we provide construction schemes for optimal TSPFN tours for the considered cases.

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  1. 1.

    Note that we rotated the m-n-coordinate system of the Euclidean plane by 90\(^\circ \) in clockwise direction in order to work with the usual matrix numbering of the grid cells later on.

  2. 2.

    In slight abuse of notation we will often write in this paper that a path has a start (the first node mentioned) and an end vertex (the last node mentioned) although we are in the undirected case.

  3. 3.

    The only exception is in the upper left corner, when we go from (1, 3) to (1, 1) and then over (2, 2), to (3, 3) and (4, 4).


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We thank Richard Kordaß and Thomas Töppel from the Fraunhofer IWU in Dresden for introducing us to this optimization problem in laser beam melting and for providing several real-world instances.

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Correspondence to Anja Fischer.

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Fischer, A., Hungerländer, P. The traveling salesman problem on grids with forbidden neighborhoods. J Comb Optim 34, 891–915 (2017).

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  • Shortest Hamiltonian path problem
  • Traveling salesman problem
  • Constrained Euclidean traveling salesman problem
  • Grid
  • Explicit solutions

Mathematics Subject Classification

  • 90C27
  • 05C38