Creative Commons Attribution 3.0 Unported license
We present several sparsification lower and upper bounds for classic problems in graph theory and logic. For the problems 4-Coloring, (Directed) Hamiltonian Cycle, and (Connected) Dominating Set, we prove that there is no polynomial-time algorithm that reduces any n-vertex input to an equivalent instance, of an arbitrary problem, with bitsize O(n^{2-epsilon}) for epsilon > 0, unless NP is a subset of coNP/poly and the polynomial-time hierarchy collapses. These results imply that existing linear-vertex kernels for k-Nonblocker and k-Max Leaf Spanning Tree (the parametric duals of (Connected) Dominating Set) cannot be improved to have O(k^{2-epsilon}) edges, unless NP is a subset of NP/poly. We also present a positive result and exhibit a non-trivial sparsification algorithm for d-Not-All-Equal-SAT. We give an algorithm that reduces an n-variable input with clauses of size at most d to an equivalent input with O(n^{d-1}) clauses, for any fixed d. Our algorithm is based on a linear-algebraic proof of Lovász that bounds the number of hyperedges in critically 3-chromatic d-uniform n-vertex hypergraphs by binom{n}{d-1}. We show that our kernel is tight under the assumption that NP is not a subset of NP/poly.
@InProceedings{jansen_et_al:LIPIcs.IPEC.2015.163,
author = {Jansen, Bart M. P. and Pieterse, Astrid},
title = {{Sparsification Upper and Lower Bounds for Graphs Problems and Not-All-Equal SAT}},
booktitle = {10th International Symposium on Parameterized and Exact Computation (IPEC 2015)},
pages = {163--174},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-939897-92-7},
ISSN = {1868-8969},
year = {2015},
volume = {43},
editor = {Husfeldt, Thore and Kanj, Iyad},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.IPEC.2015.163},
URN = {urn:nbn:de:0030-drops-55806},
doi = {10.4230/LIPIcs.IPEC.2015.163},
annote = {Keywords: sparsification, graph coloring, Hamiltonian cycle, satisfiability}
}