Computing tree decompositions with small independence numberDallard, Clément Jean (Avtor) Fomin, Fedor V. (Avtor) Golovach, Petr A. (Avtor) Korhonen, Tuukka (Avtor) Milanič, Martin (Avtor) tree-independence numberapproximationparameterized algorithmThe independence number of a tree decomposition is the maximum of the independence numbers of the subgraphs induced by its bags. The tree-independence number of a graph is the minimum independence number of a tree decomposition of it. Several NP-hard graph problems, like maximum-weight independent set, can be solved in time n^O(k) if the input n-vertex graph is given together with a tree decomposition of independence number k. Yolov, in SODA 2018, gave an algorithm that, given an n-vertex graph G and an integer k, in time n^O(k^3) either constructs a tree decomposition of G whose independence number is O(k^3) or correctly reports that the tree-independence number of G is larger than k. In this article, we first give an algorithm for computing the tree-independence number with a better approximation ratio and running time and then prove that our algorithm is, in some sense, the best one can hope for. Our second result is that the exact computation of the tree-independence number is para-NP-hard: We show that for every constant k ≥ 4 it is NP-complete to decide whether a given graph has the tree-independence number at most k.20262025-12-16 17:51:13Članek v reviji22213UDK: 51ISSN pri članku: 1549-6325DOI: 10.1145/3767730COBISS.SI-ID: 261744131sl