The Complexity of Lifted Inequalities for the Knapsack Problem

Hartvigsen, D. and E. Zemel, The complexity of lifted inequalities for the knapsack problem, Discrete Applied Mathematics 39 (1992) 11. 123. It is well known that one can obtain facets and valid inequalities for the knapsack polytope by lifting simple inequalities associated with minimal covers. We study the complexity of lifting. We show that recognizing integral lifted facets or valid inequalities can be done in O(n”) time, even if the minimal cover from which they are lifted is not given. We show that the complexities of recognizing nonintegral lifted facets and valid inequalities are similar, respectively, to those of recognizing general (not necessarily lifted) facets and valid inequalities. Finally, we show that recognizing valid inequalitles is in coNPC while recognizing facets is in Dp. The question of whether recognizing facets is complete for LY’ is open.