We prove upper bounds on the graph diameters of polytopes in two settings. The first is a worst-case bound for integer polytopes in terms of the length of the description of the polytope (in bits) and the minimum angle between facets of its polar. The second is a smoothed analysis bound: given an appropriately normalized polytope, we add small Gaussian noise to each constraint. We consider a natural geometric measure on the vertices of the perturbed polytope (corresponding to the mean curvature measure of its polar) and show that with high probability there exists a "giant component" of vertices, with measure 1-o(1) and polynomial diameter. Both bounds rely on spectral gaps - of a certain Schrödinger operator in the first case, and a certain continuous time Markov chain in the second - which arise from the log-concavity of the volume of a simple polytope in terms of its slack variables.
@InProceedings{narayanan_et_al:LIPIcs.ITCS.2022.108, author = {Narayanan, Hariharan and Shah, Rikhav and Srivastava, Nikhil}, title = {{A Spectral Approach to Polytope Diameter}}, booktitle = {13th Innovations in Theoretical Computer Science Conference (ITCS 2022)}, pages = {108:1--108:22}, series = {Leibniz International Proceedings in Informatics (LIPIcs)}, ISBN = {978-3-95977-217-4}, ISSN = {1868-8969}, year = {2022}, volume = {215}, editor = {Braverman, Mark}, publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik}, address = {Dagstuhl, Germany}, URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ITCS.2022.108}, URN = {urn:nbn:de:0030-drops-157044}, doi = {10.4230/LIPIcs.ITCS.2022.108}, annote = {Keywords: Polytope diameter, Markov Chain} }
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