Backdoor Branching

  • Authors:
  • Matteo Fischetti;Michele Monaci

  • Affiliations:
  • Department of Information Engineering, University of Padova, 35131 Padova, Italy;Department of Information Engineering, University of Padova, 35131 Padova, Italy

  • Venue:
  • INFORMS Journal on Computing
  • Year:
  • 2013

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Abstract

We present an exact mixed-integer programming MIP solution scheme where a set-covering model is used to find a small set of first-choice branching variables. In a preliminary “sampling” phase, our method quickly collects a number of relevant low-cost fractional solutions that qualify as obstacles for the linear programming LP relaxation bound improvement. Then a set covering model is solved to detect a small subset of variables a “backdoor,” in the artificial intelligence jargon that “cover the fractionality” of the collected fractional solutions. These backdoor variables are put in a priority branching list, and a black-box MIP solver is eventually run---in its default mode---by taking this list into account, thus avoiding any other interference with its highly optimized internal mechanisms. Computational results on a large set of instances from the literature are presented, showing that some speedup can be achieved even with respect to a state-of-the-art solver such as IBM ILOG CPLEX 12.2.