Hard Equality Constrained Integer Knapsacks

  • Authors:
  • Karen Aardal;Arjen K. Lenstra

  • Affiliations:
  • -;-

  • Venue:
  • Mathematics of Operations Research
  • Year:
  • 2004

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Abstract

We consider the following integer feasibility problem: Given positive integer numbersa0,a1, ... , a n , with gcd( a1,..., a n ) = 1 anda = ( a1,..., a n ), does there exist a vectorx?Z n =0satisfyinga x= a0? We prove that if the coefficientsa1,..., a nhave a certain decomposable structure, then the Frobenius number associated witha1,..., a n , i.e., the largest value ofa0 for whicha x= a0 does not have a nonnegative integer solution, is close to a known upper bound. In the instances we consider, we takea0 to be the Frobenius number. Furthermore, we show that the decomposable structure ofa1,..., a nmakes the solution of a lattice reformulation of our problem almost trivial, since the number of lattice hyperplanes that intersect the polytope resulting from the reformulation in the direction of the last coordinate is going to be very small. For branch-and-bound such instances are difficult to solve, since they are infeasible and have large values ofa0/ a i , 1= i= n. We illustrate our results by some computational examples.