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arXiv · 2210.13395

Improved Bi-point Rounding Algorithms and a Golden Barrier for $k$-Median

Kishen N. Gowda·Thomas Pensyl·Aravind Srinivasan·Khoa Trinh
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Abstract

The current best approximation algorithms for $k$-median rely on first obtaining a structured fractional solution known as a bi-point solution, and then rounding it to an integer solution. We improve this second step by unifying and refining previous approaches. We describe a hierarchy of increasingly-complex partitioning schemes for the facilities, along with corresponding sets of algorithms and factor-revealing non-linear programs. We prove that the third layer of this hierarchy is a $2.613$-approximation, improving upon the current best ratio of $2.675$, while no layer can be proved better than $2.588$ under the proposed analysis. On the negative side, we give a family of bi-point solutions which cannot be approximated better than the square root of the golden ratio, even if allowed to open $k+o(k)$ facilities. This gives a barrier to current approaches for obtaining an approximation better than $2 \sqrt{\phi} \approx 2.544$. Altogether we reduce the approximation gap of bi-point solutions by two thirds.

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Kishen N. Gowda, Thomas Pensyl, Aravind Srinivasan, Khoa Trinh. 2022-10-24. Improved Bi-point Rounding Algorithms and a Golden Barrier for $k$-Median. https://arxiv.org/abs/2210.13395

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