Well-solvable special cases of the TSP : a survey

The Traveling Salesman Problem belongs to the most important and most investigated problems in combinatorial optimization. Although it is an NP-hard problem, many of its special cases can be solved efficiently. We survey these special cases with emphasis on results obtained during the decade 1985-1995. This survey complements an earlier survey from 1985 compiled by Gilmore, Lawler and Shmoys. Keywords: Traveling Salesman Problem, Combinatorial optimization, Polynomial time algorithm, Computational complexity

A well-solvable special case of the bounded knapsack problem

We identify a polynomially solvable special case of the bounded knapsack problem that is characterized by a set of simple inequalities relating item weight ratios to item profit ratios. Our result generalizes and extends a corresponding result of Zukerman, et al. [M. Zukerman, L. Jia, T. Neame, G.J. Woeginger, A polynomially solvable special case of the unbounded knapsack problem, Operations Research Letters 29 (2001) 13–16] for the unbounded knapsack problem

Some problems around travelling salesmen, dart boards, and Euro-coins

In 1957 Fred Supnick investigated and solved a special case of the Travelling Salesman Problem. Since then, Supnick's results have been rediscovered many times by other researchers. This article discusses Supnick's results and some of the rediscoveries

A study of exponential neighborhoods for the Travelling Salesman Problem and for the Quadratic Assignment Problem

This paper deals with exponential neighborhoods for combinatorial optimization problems. Exponential neighborhoods are large sets of feasible solutions whose size grows exponentially with the input length. We are especially interested in exponential neighborhoods over which the TSP (respectively, the QAP) can be solved in polynomial time, and we investigate combinatorial and algorithmical questions related to such neighborhoods.First, we perform a careful study of exponential neighborhoods for the TSP. We investigate neighborhoods that can be defined in a simple way via assignments, matchings in bipartite graphs, partial orders, trees and other combinatorial structures. We identify several properties of these combinatorial structures that lead to polynomial time optimization algorithms, and we also provide variants that slightly violate these properties and lead to NP-complete optimization problems. Whereas it is relatively easy to find exponential neighborhoods over which the TSP can be solved in polynomial time, the corresponding situation for the QAP looks pretty hopeless: Every exponential neighborhood that is considered in this paper provably leads to an NP-complete optimization problem for the QAP

A solvable case of the quadratic assignment problem

This short note investigates a restricted version of the quadratic assignment problem (QAP), where one of the coefficient matrices is a Kalmanson matrix, and where the other coefficient matrix is a symmetric circulant matrix that is generated by a decreasing function. This restricted version is called the Kalmanson-circulant QAP. We prove that – in strong contrast to the general QAP – this version can be solved easily. Our result naturally generalizes a well-known theorem of Kalmanson on the travelling salesman problem

Some problems around travelling salesmen, dart boards, and Euro-coins

In 1957 Fred Supnick investigated and solved a special case of the Travelling Salesman Problem. Since then, Supnick's results have been rediscovered many times by other researchers. This article discusses Supnick's results and some of the rediscoveries

On the dimension of simple monotonic games

We show that the following problem is NP-hard, and hence computationally intractable: "Given d weighted majority games, decide whether the dimension of their intersection exactly equals d". Our result indicates that the dimension of simple monotonic games is a combinatorially complicated concept

The maximum Travelling Salesman Problem on symmetric Demidenko matrices

It is well-known that the Travelling Salesman Problem (TSP) is solvable in polynomial time, if the distance matrix fulfills the so-called Demidenko conditions. This paper investigates the closely related Maximum Travelling Salesman Problem (MaxTSP) on symmetric Demidenko matrices. Somewhat surprisingly, we show that — in strong contrast to the minimization problem — the maximization problem is NP-hard to solve. Moreover, we identify several special cases that are solvable in polynomial time. These special cases contain and generalize several predecessor results by Quintas and Supnick and by Kalmanson