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DOI: 10.4230/LIPIcs.APPROX-RANDOM.2019.48
URN: urn:nbn:de:0030-drops-112630
URL: https://drops.dagstuhl.de/opus/volltexte/2019/11263/
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Efthymiou, Charilaos ; Galanis, Andreas ; Hayes, Thomas P. ; Stefankovic, Daniel ; Vigoda, Eric

Improved Strong Spatial Mixing for Colorings on Trees

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LIPIcs-APPROX-RANDOM-2019-48.pdf (0.5 MB)


Abstract

Strong spatial mixing (SSM) is a form of correlation decay that has played an essential role in the design of approximate counting algorithms for spin systems. A notable example is the algorithm of Weitz (2006) for the hard-core model on weighted independent sets. We study SSM for the q-colorings problem on the infinite (d+1)-regular tree. Weak spatial mixing (WSM) captures whether the influence of the leaves on the root vanishes as the height of the tree grows. Jonasson (2002) established WSM when q>d+1. In contrast, in SSM, we first fix a coloring on a subset of internal vertices, and we again ask if the influence of the leaves on the root is vanishing. It was known that SSM holds on the (d+1)-regular tree when q>alpha d where alpha ~~ 1.763... is a constant that has arisen in a variety of results concerning random colorings. Here we improve on this bound by showing SSM for q>1.59d. Our proof establishes an L^2 contraction for the BP operator. For the contraction we bound the norm of the BP Jacobian by exploiting combinatorial properties of the coloring of the tree.

BibTeX - Entry

@InProceedings{efthymiou_et_al:LIPIcs:2019:11263,
  author =	{Charilaos Efthymiou and Andreas Galanis and Thomas P. Hayes and Daniel Stefankovic and Eric Vigoda},
  title =	{{Improved Strong Spatial Mixing for Colorings on Trees}},
  booktitle =	{Approximation, Randomization, and Combinatorial Optimization. Algorithms and Techniques (APPROX/RANDOM 2019)},
  pages =	{48:1--48:16},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-125-2},
  ISSN =	{1868-8969},
  year =	{2019},
  volume =	{145},
  editor =	{Dimitris Achlioptas and L{\'a}szl{\'o} A. V{\'e}gh},
  publisher =	{Schloss Dagstuhl--Leibniz-Zentrum fuer Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{http://drops.dagstuhl.de/opus/volltexte/2019/11263},
  URN =		{urn:nbn:de:0030-drops-112630},
  doi =		{10.4230/LIPIcs.APPROX-RANDOM.2019.48},
  annote =	{Keywords: colorings, regular tree, spatial mixing, phase transitions}
}

Keywords: colorings, regular tree, spatial mixing, phase transitions
Seminar: Approximation, Randomization, and Combinatorial Optimization. Algorithms and Techniques (APPROX/RANDOM 2019)
Issue Date: 2019
Date of publication: 19.09.2019


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