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List Homomorphism: Beyond the Known Boundaries
S. Bhyravarapu, S. Jana, , S. Saurabh, S. Verma
Published in Springer Science and Business Media Deutschland GmbH
2022
Volume: 13568 LNCS
   
Pages: 593 - 609
Abstract
Given two graphs G and H, and a list L(u) ⊆ V(H) associated with each u∈ V(G), a list homomorphism from G to H is a mapping f: V(G) → V(H) such that (i) for all u∈ V(G), f(u) ∈ L(u), and (ii) for all u, v∈ V(G), if uv∈ E(G) then f(u) f(v) ∈ E(H). The List Homomorphism problem asks whether there exists a list homomorphism from G to H. Enright, Stewart and Tardos [SIAM J. Discret. Math., 2014] showed that the List Homomorphism problem can be solved in O(nk2-3k+4) time on graphs where every connected induced subgraph of G admits “a multichain ordering” (see the introduction for the definition of multichain ordering of a graph), that includes permutation graphs, biconvex graphs, and interval graphs, where n= | V(G) | and k= | V(H) |. We prove that List Homomorphism parameterized by k even when G is a bipartite permutation graph is W[1]-hard. In fact, our reduction implies that it is not solvable in time no(k), unless the Exponential Time Hypothesis (ETH) fails. We complement this result with a matching upper bound and another positive result. 1.There is a O(n8k+3) time algorithm for List Homomorphism on bipartite graphs that admit a multichain ordering that includes the class of bipartite permutation graphs and biconvex graphs.2.For bipartite graph G that admits a multichain ordering, List Homomorphism is fixed parameter tractable when parameterized by k and the number of layers in the multichain ordering of G. In addition, we study a variant of List Homomorphism called List Locally Surjective Homomorphism. We prove that List Locally Surjective Homomorphism parameterized by the number of vertices in H is W[1]-hard, even when G is a chordal graph and H is a split graph. © 2022, Springer Nature Switzerland AG.
About the journal
JournalLecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics)
PublisherSpringer Science and Business Media Deutschland GmbH
ISSN03029743