Abstract
Sparse structures are frequently sought when pursuing tractability in optimization problems. They are exploited from both theoretical and computational perspectives to handle complex problems that become manageable when sparsity is present. An example of this type of structure is given by treewidth: a graph theoretical parameter that measures how “tree-like” a graph is. This parameter has been used for decades for analyzing the complexity of various optimization problems and for obtaining tractable algorithms for problems where this parameter is bounded. The goal of this work is to contribute to the understanding of the limits of the treewidth-based tractability in optimization. Our results are as follows. First, we prove that, in a certain sense, the already known positive results on extension complexity based on low treewidth are the best possible. Secondly, under mild assumptions, we prove that treewidth is the only graph-theoretical parameter that yields tractability for a wide class of optimization problems, a fact well known in Graphical Models in Machine Learning and in Constraint Satisfaction Problems, which here we extend to an approximation setting in Optimization.
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Notes
Sometimes called primal constraint graph or Gaifman graph.
Probability at least \(1 - 1/|V(G)|^c\) for some constant \(c>1\).
By equivalent, we mean that feasible solutions of one optimization problem can be mapped to feasible solutions of the other with the same objective value, and vice-versa.
Existence is proven by a counting argument, and it is thus a non-constructive proof. It remains open to find such a family constructively.
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Acknowledgements
We would like to thank the anonymous reviewers whose suggestions greatly helped improving this article. Research reported in this paper was partially supported by NSF CAREER award CMMI-1452463 and by the Institute for Data Valorisation (IVADO).
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Faenza, Y., Muñoz, G. & Pokutta, S. New limits of treewidth-based tractability in optimization. Math. Program. 191, 559–594 (2022). https://doi.org/10.1007/s10107-020-01563-5
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DOI: https://doi.org/10.1007/s10107-020-01563-5