Hard Equality Constrained Integer Knapsacks

  • Authors:
  • Karen Aardal;Arjen K. Lenstra

  • Affiliations:
  • -;-

  • Venue:
  • Proceedings of the 9th International IPCO Conference on Integer Programming and Combinatorial Optimization
  • Year:
  • 2002

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Abstract

We consider the following integer feasibility problem: "Given positive integer numbers a0, a1,..., an, with gcd(a1,..., an) = 1 and a = (a1,..., an), does there exist a nonnegative integer vector x satisfying ax = a0?" Some instances of this type have been found to be extremely hard to solve by standard methods such as branch-and-bound, even if the number of variables is as small as ten. We observe that not only the sizes of the numbers a0, a1,..., an, but also their structure, have a large impact on the difficulty of the instances. Moreover, we demonstrate that the characteristics that make the instances so difficult to solve by branch-and-bound make the solution of a certain reformulation of the problem almost trivial. We accompany our results by a small computational study.