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Approximating Sparsest Cut in Low-treewidth Graphs via Combinatorial Diameter

Published: 22 January 2024 Publication History

Abstract

The fundamental Sparsest Cut problem takes as input a graph G together with edge capacities and demands and seeks a cut that minimizes the ratio between the capacities and demands across the cuts. For n-vertex graphs G of treewidth k, Chlamtáč, Krauthgamer, and Raghavendra (APPROX’10) presented an algorithm that yields a factor-\(2^{2^k}\) approximation in time \(2^{O(k)} \cdot n^{O(1)}\). Later, Gupta, Talwar, and Witmer (STOC’13) showed how to obtain a 2-approximation algorithm with a blown-up runtime of \(n^{O(k)}\). An intriguing open question is whether one can simultaneously achieve the best out of the aforementioned results, that is, a factor-2 approximation in time \(2^{O(k)} \cdot n^{O(1)}\).
In this article, we make significant progress towards this goal via the following results:
(i)
A factor-\(O(k^2)\) approximation that runs in time \(2^{O(k)} \cdot n^{O(1)}\), directly improving the work of Chlamtáč et al. while keeping the runtime single-exponential in k.
(ii)
For any \(\varepsilon \in (0,1]\), a factor-\(O(1/\varepsilon ^2)\) approximation whose runtime is \(2^{O(k^{1+\varepsilon }/\varepsilon)} \cdot n^{O(1)}\), implying a constant-factor approximation whose runtime is nearly single-exponential in k and a factor-\(O(\log ^2 k)\) approximation in time \(k^{O(k)} \cdot n^{O(1)}\).
Key to these results is a new measure of a tree decomposition that we call combinatorial diameter, which may be of independent interest.

References

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Published In

cover image ACM Transactions on Algorithms
ACM Transactions on Algorithms  Volume 20, Issue 1
January 2024
297 pages
EISSN:1549-6333
DOI:10.1145/3613497
  • Editor:
  • Edith Cohen
Issue’s Table of Contents

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Association for Computing Machinery

New York, NY, United States

Publication History

Published: 22 January 2024
Online AM: 14 November 2023
Accepted: 30 October 2023
Revised: 09 October 2023
Received: 26 September 2021
Published in TALG Volume 20, Issue 1

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Author Tags

  1. Sparsest cut
  2. treewidth
  3. approximation algorithms
  4. parameterized complexity

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  • Research-article

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  • European Research Council (ERC)
  • European Union’s Horizon 2020
  • Academy of Finland Research Fellowship
  • French National Research Agency (ANR)

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