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Creative Commons Attribution 4.0 International license (CC BY 4.0)
When quoting this document, please refer to the following
DOI: 10.4230/LIPIcs.STACS.2021.54
URN: urn:nbn:de:0030-drops-136990
URL: http://dagstuhl.sunsite.rwth-aachen.de/volltexte/2021/13699/
Okrasa, Karolina ;
Rzążewski, Paweł
Complexity of the List Homomorphism Problem in Hereditary Graph Classes
Abstract
A homomorphism from a graph G to a graph H is an edge-preserving mapping from V(G) to V(H). For a fixed graph H, in the list homomorphism problem, denoted by LHom(H), we are given a graph G, whose every vertex v is equipped with a list L(v) ⊆ V(H). We ask if there exists a homomorphism f from G to H, in which f(v) ∈ L(v) for every v ∈ V(G). Feder, Hell, and Huang [JGT 2003] proved that LHom(H) is polynomial time-solvable if H is a so-called bi-arc-graph, and NP-complete otherwise.
We are interested in the complexity of the LHom(H) problem in F-free graphs, i.e., graphs excluding a copy of some fixed graph F as an induced subgraph. It is known that if F is connected and is not a path nor a subdivided claw, then for every non-bi-arc graph the LHom(H) problem is NP-complete and cannot be solved in subexponential time, unless the ETH fails. We consider the remaining cases for connected graphs F.
If F is a path, we exhibit a full dichotomy. We define a class called predacious graphs and show that if H is not predacious, then for every fixed t the LHom(H) problem can be solved in quasi-polynomial time in P_t-free graphs. On the other hand, if H is predacious, then there exists t, such that the existence of a subexponential-time algorithm for LHom(H) in P_t-free graphs would violate the ETH.
If F is a subdivided claw, we show a full dichotomy in two important cases: for H being irreflexive (i.e., with no loops), and for H being reflexive (i.e., where every vertex has a loop). Unless the ETH fails, for irreflexive H the LHom(H) problem can be solved in subexponential time in graphs excluding a fixed subdivided claw if and only if H is non-predacious and triangle-free. On the other hand, if H is reflexive, then LHom(H) cannot be solved in subexponential time whenever H is not a bi-arc graph.
BibTeX - Entry
@InProceedings{okrasa_et_al:LIPIcs.STACS.2021.54,
author = {Okrasa, Karolina and Rz\k{a}\.{z}ewski, Pawe{\l}},
title = {{Complexity of the List Homomorphism Problem in Hereditary Graph Classes}},
booktitle = {38th International Symposium on Theoretical Aspects of Computer Science (STACS 2021)},
pages = {54:1--54:17},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-180-1},
ISSN = {1868-8969},
year = {2021},
volume = {187},
editor = {Bl\"{a}ser, Markus and Monmege, Benjamin},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/opus/volltexte/2021/13699},
URN = {urn:nbn:de:0030-drops-136990},
doi = {10.4230/LIPIcs.STACS.2021.54},
annote = {Keywords: list homomorphism, fine-grained complexity, hereditary graph classes}
}
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Keywords: |
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list homomorphism, fine-grained complexity, hereditary graph classes |
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Collection: |
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38th International Symposium on Theoretical Aspects of Computer Science (STACS 2021) |
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Issue Date: |
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2021 |
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Date of publication: |
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10.03.2021 |
