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Isoperimetric inequalities in simplicial complexes. (English) Zbl 1389.05174
Authors’ abstract: In graph theory there are intimate connections between the expansion properties of a graph and the spectrum of its Laplacian. In this paper we define a notion of combinatorial expansion for simplicial complexes of general dimension, and prove that similar connections exist between the combinatorial expansion of a complex, and the spectrum of the high dimensional Laplacian defined by Eckmann. In particular, we present a Cheeger-type inequality, and a high-dimensional expander mixing lemma. As a corollary, using the work of J. Pach [Comput. Geom. 10, No. 2, 71–76 (1998; Zbl 0896.68143)], we obtain a connection between spectral properties of complexes and Gromov’s notion of geometric overlap. Using the work of A. Gundert and U. Wagner [in: Proceedings of the 28th annual symposium on computational geometry, SoCG 2012, Chapel Hill, NC, USA, June 17–20, 2012. New York, NY: Association for Computing Machinery (ACM). 151–160 (2012; Zbl 1293.05210)], we give an estimate for the combinatorial expansion and geometric overlap of random Linial-Meshulam complexes.
Reviewer’s remark: Finally, five open questions are proposed.

##### MSC:
 05E45 Combinatorial aspects of simplicial complexes 05C80 Random graphs (graph-theoretic aspects) 55U10 Simplicial sets and complexes in algebraic topology 35P05 General topics in linear spectral theory for PDEs
##### Citations:
Zbl 0896.68143; Zbl 1293.05210
Full Text:
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