0/1 polytopes with quadratic chvátal rank

  • Authors:
  • Thomas Rothvoß;Laura Sanitá

  • Affiliations:
  • MIT, Boston;University of Waterloo, Canada

  • Venue:
  • IPCO'13 Proceedings of the 16th international conference on Integer Programming and Combinatorial Optimization
  • Year:
  • 2013
  • Reverse chvátal-gomory rank

    IPCO'13 Proceedings of the 16th international conference on Integer Programming and Combinatorial Optimization

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Abstract

For a polytope P, the Chvátal closureP′⊆P is obtained by simultaneously strengthening all feasible inequalities cx≤β (with integral c) to $cx \leq \lfloor\beta\rfloor$. The number of iterations of this procedure that are needed until the integral hull of P is reached is called the Chvátal rank. If P⊆[0,1]n, then it is known that O(n2 logn) iterations always suffice (Eisenbrand and Schulz (1999)) and at least $(1+\frac{1}{e}-o(1))n$ iterations are sometimes needed (Pokutta and Stauffer (2011)), leaving a huge gap between lower and upper bounds. We prove that there is a polytope contained in the 0/1 cube that has Chvátal rank Ω(n2), closing the gap up to a logarithmic factor. In fact, even a superlinear lower bound was mentioned as an open problem by several authors. Our choice of P is the convex hull of a semi-random Knapsack polytope and a single fractional vertex. The main technical ingredient is linking the Chvátal rank to simultaneous Diophantine approximations w.r.t. the ∥·∥1-norm of the normal vector defining P.