Adaptive Massively Parallel Coloring in Sparse Graphs

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A4 Artikkeli konferenssijulkaisussa

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en

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11

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PODC 2024 - Proceedings of the 2024 ACM Symposium on Principles of Distributed Computing, pp. 508-518

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Classic symmetry-breaking problems on graphs have gained a lot of attention in models of modern parallel computation. The Adaptive Massively Parallel Computation (AMPC) is a model that captures the central challenges in data center computations. Chang et al. [PODC'2019] gave an extremely fast, constant time, algorithm for the (δ+1)-coloring problem, where Δis the maximum degree of an input graph of n nodes. The algorithm works in the most restrictive low-space setting, where each machine has nδ local space for a constant 0 < δ < 1.The standard approaches for (Δ+ 1)-coloring are ignorant about the graph topology in the following sense: They exploit the property that any partial coloring can be extended to a feasible (Δ+ 1)-coloring of the whole graph. For most graphs, the chromatic number is much smaller than Δ+ 1 and we would like to find colorings with fewer colors. However, as soon as we have fewer than Δ+ 1 colors, it might not be possible to complete partial colorings.In this work, we study the vertex-coloring problem in sparse graphs parameterized by their arboricity α, a standard measure for sparsity. We give deterministic algorithms that in constant, or almost constant, time give poly α and O(α)-colorings, where α can be arbitrarily smaller than δ. A strong and standard approach to compute arboricity-dependent colorings is through the Nash-Williams forest decomposition, which gives rise to an (acyclic) orientation of the edges such that each node has a small out-degree.Our main technical contribution is giving efficient deterministic algorithms to compute these orientations and showing how to leverage them to find colorings in low-space AMPC. A key technical challenge is that the color of a node may depend on almost all of the other nodes in the graph and these dependencies cannot be stored on a single machine. Nevertheless, our novel and careful exploration technique yields the orientation, and the arboricity-dependent coloring, with a sublinear number of adaptive queries per node.

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Publisher Copyright: © 2024 Association for Computing Machinery. All rights reserved.

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Latypov, R, Maus, Y, Pai, S & Uitto, J 2024, Adaptive Massively Parallel Coloring in Sparse Graphs. in PODC 2024 - Proceedings of the 2024 ACM Symposium on Principles of Distributed Computing. ACM, pp. 508-518, ACM Symposium on Principles of Distributed Computing, Nantes, France, 17/06/2024. https://doi.org/10.1145/3662158.3662821