,
Euiwoong Lee
,
Pasin Manurangsi
Creative Commons Attribution 4.0 International license
Parameterized Inapproximability Hypothesis (PIH) is a central question in the field of parameterized complexity. PIH asserts that given as input a 2-CSP on k variables and alphabet size n, it is 𝖶[1]-hard parameterized by k to distinguish if the input is perfectly satisfiable or if every assignment to the input violates 1% of the constraints. An important implication of PIH is that it yields the tight parameterized inapproximability of the k-maxcoverage problem. In the k-maxcoverage problem, we are given as input a set system, a threshold τ > 0, and a parameter k and the goal is to determine if there exist k sets in the input whose union is at least τ fraction of the entire universe. PIH is known to imply that it is 𝖶[1]-hard parameterized by k to distinguish if there are k input sets whose union is at least τ fraction of the universe or if the union of every k input sets is not much larger than τ⋅ (1-1/e) fraction of the universe. In this work we present a gap preserving FPT reduction (in the reverse direction) from the k-maxcoverage problem to the aforementioned 2-CSP problem, thus showing that the assertion that approximating the k-maxcoverage problem to some constant factor is 𝖶[1]-hard implies PIH. In addition, we present a gap preserving FPT reduction from the k-median problem (in general metrics) to the k-maxcoverage problem, further highlighting the power of gap preserving FPT reductions over classical gap preserving polynomial time reductions.
@InProceedings{karthikc.s._et_al:LIPIcs.IPEC.2024.6,
author = {Karthik C. S. and Lee, Euiwoong and Manurangsi, Pasin},
title = {{On Equivalence of Parameterized Inapproximability of k-Median, k-Max-Coverage, and 2-CSP}},
booktitle = {19th International Symposium on Parameterized and Exact Computation (IPEC 2024)},
pages = {6:1--6:18},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-353-9},
ISSN = {1868-8969},
year = {2024},
volume = {321},
editor = {Bonnet, \'{E}douard and Rz\k{a}\.{z}ewski, Pawe{\l}},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.IPEC.2024.6},
URN = {urn:nbn:de:0030-drops-222322},
doi = {10.4230/LIPIcs.IPEC.2024.6},
annote = {Keywords: Parameterized complexity, Hardness of Approximation, Parameterized Inapproximability Hypothesis, max coverage, k-median}
}