Embedding Formulations and Complexity for Unions of Polyhedra

Published Online:https://doi.org/10.1287/mnsc.2017.2856

It is well known that selecting a good mixed-integer programming (MIP) formulation is crucial for effectively obtaining a solution with state-of-the art solvers. Although best practices and guidelines for constructing good formulations abound, there is rarely a single systematic construction approach that leads to the best possible formulation. Here, we introduce embedding formulations and complexity as a new MIP formulation paradigm for systematically constructing formulations for disjunctive constraints that are optimal with respect to size. More specifically, they yield the smallest possible ideal formulation (i.e., one whose LP relaxation has integral extreme points) among all formulations that only use 0-1 auxiliary variables. We use the paradigm to characterize optimal formulations for special ordered sets of type 2 and certain piecewise linear functions of two variables. We also show that the resultant formulations can provide a significant computational advantage over all known formulations for piecewise linear functions.

This paper was accepted by Yinyu Ye, optimization.

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