Please use this identifier to cite or link to this item: http://hdl.handle.net/2445/33855
 Title: Sherali-Adams Relaxations and Indistinguishability in Counting Logics Author: Atserias, AlbertManeva, Elitza Keywords: Lògica de primer ordreProgramació linealTeoria de grafsFirst-order logicLinear programmingGraph theory Issue Date: 17-Jan-2013 Publisher: Society for Industrial and Applied Mathematics Abstract: Two graphs with adjacency matrices $\mathbf{A}$ and $\mathbf{B}$ are isomorphic if there exists a permutation matrix $\mathbf{P}$ for which the identity $\mathbf{P}^{\mathrm{T}} \mathbf{A} \mathbf{P} = \mathbf{B}$ holds. Multiplying through by $\mathbf{P}$ and relaxing the permutation matrix to a doubly stochastic matrix leads to the linear programming relaxation known as fractional isomorphism. We show that the levels of the Sherali--Adams (SA) hierarchy of linear programming relaxations applied to fractional isomorphism interleave in power with the levels of a well-known color-refinement heuristic for graph isomorphism called the Weisfeiler--Lehman algorithm, or, equivalently, with the levels of indistinguishability in a logic with counting quantifiers and a bounded number of variables. This tight connection has quite striking consequences. For example, it follows immediately from a deep result of Grohe in the context of logics with counting quantifiers that a fixed number of levels of SA suffice to determine isomorphism of planar and minor-free graphs. We also offer applications in both finite model theory and polyhedral combinatorics. First, we show that certain properties of graphs, such as that of having a flow circulation of a prescribed value, are definable in the infinitary logic with counting with a bounded number of variables. Second, we exploit a lower bound construction due to Cai, Fürer, and Immerman in the context of counting logics to give simple explicit instances that show that the SA relaxations of the vertex-cover and cut polytopes do not reach their integer hulls for up to $\Omega(n)$ levels, where $n$ is the number of vertices in the graph. Note: Reproducció del document publicat a: http://dx.doi.org/10.1137/120867834 It is part of: SIAM Journal on Computing, 2013, vol. 42, num. 1, p. 112-137 Related resource: http://dx.doi.org/10.1137/120867834 URI: http://hdl.handle.net/2445/33855 ISSN: 0097-5397 Appears in Collections: Articles publicats en revistes (Matemàtiques i Informàtica)

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