Title
FINDING LARGE H-COLORABLE SUBGRAPHS IN HEREDITARY GRAPH CLASSES
Abstract
We study the MAX PARTIAL H-COLORING problem: given a graph G, find the largest induced subgraph of G that admits a homomorphism into H, where H is a fixed pattern graph without loops. Note that when H is a complete graph on k vertices, the problem reduces to finding the largest induced k-colorable subgraph, which for k = 2 is equivalent (by complementation) to ODD CYCLE TRANSVERSAL. We prove that for every fixed pattern graph H without loops, MAX PARTIAL H-COLORING can be solved in {P-5, F}-free graphs in polynomial time, whenever F is a threshold graph; in {P-5, bull}-free graphs in polynomial time; in P-5-free graphs in time n(O(omega(G))); and in {P-6, 1-subdivided claw}-free graphs in time n(O(omega(G)3)). Here, n is the number of vertices of the input graph G and omega(G) is the maximum size of a clique in G. Furthermore, by combining the mentioned algorithms for P-5-free and for {P-6, 1-subdivided claw}-free graphs with a simple branching procedure, we obtain subexponential-time algorithms for MAX PARTIAL H-COLORING in these classes of graphs. Finally, we show that even a restricted variant of MAX PARTIAL H-COLORING is NP-hard in the considered subclasses of P-5-free graphs if we allow loops on H.
Year
DOI
Venue
2021
10.1137/20M1367660
SIAM JOURNAL ON DISCRETE MATHEMATICS
Keywords
DocType
Volume
odd cycle transversal, graph homomorphism, P-5-free graphs
Journal
35
Issue
ISSN
Citations 
4
0895-4801
0
PageRank 
References 
Authors
0.34
0
5
Name
Order
Citations
PageRank
Maria Chudnovsky139046.13
Jason King200.68
michal pilipczuk340351.93
Pawel Rzazewski44219.73
Sophie Theresa Spirkl587.36