1. Computing tree decompositions with small independence numberClément Jean Dallard, Fedor V. Fomin, Petr A. Golovach, Tuukka Korhonen, Martin Milanič, 2026, original scientific article Abstract: The 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.
Keywords: tree-independence number, approximation, parameterized algorithm
Published in RUP: 16.12.2025; Views: 256; Downloads: 4
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2. On ▫$L^2$▫ approximation by planar Pythagorean-hodograph curvesRida T. Farouki, Marjetka Knez, Vito Vitrih, Emil Žagar, 2025, original scientific article Abstract: The ▫$L^2$▫ approximation of planar curves by Pythagorean-hodograph (PH) polynomial curves is addressed, based on the distance defined by a metric for planar curves represented as complex valued functions of a real parameter. Because of the nonlinear nature of polynomial PH curves, constructing ▫$L^2$▫ approximants involves solving a nonlinear optimization problem. However, a simplified method that requires only the solution of a linear system may be developed by formulating the ▫$L^2$▫ approximation in the preimage space. The extension of the methodology to approximation by PH B-spline curves is also addressed, and several examples are provided to illustrate its implementation and potential.
Keywords: ▫$L^2$▫ approximation, complex polynomial, Pythagorean-hodograph curve, Pythagorean-hodograph spline, preimage
Published in RUP: 30.05.2025; Views: 2308; Downloads: 16
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4. Scaffolding problems revisited : complexity, approximation and fixed parameter tractable algorithms, and some special casesMathias Weller, Annie Chateau, Clément Jean Dallard, Rodolphe Giroudeau, 2018, original scientific article Keywords: complexity, approximation, lower bound, kernel, scaffolding, {ISK4, wheel}-free graph
Published in RUP: 11.02.2020; Views: 2962; Downloads: 65
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7. Perfect phylogenies via branchings in acyclic digraphs and a generalization of Dilworth's theoremAdemir Hujdurović, Martin Milanič, Edin Husić, Romeo Rizzi, Alexandru I. Tomescu, 2017, published scientific conference contribution abstract Keywords: perfect phylogeny, NP-hard problem, branching, acyclic digraph, chain partition, Dilworth's theorem, min-max theorem, approximation algorithm, heuristic
Published in RUP: 17.09.2018; Views: 3876; Downloads: 125
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8. Reconstructing perfect phylogenies via binary matrices, branchings in DAGs, and a generalization of Dilworth's theoremAdemir Hujdurović, Martin Milanič, Edin Husić, Romeo Rizzi, Alexandru I. Tomescu, 2018, published scientific conference contribution abstract Keywords: perfect phylogeny, NP-hard problem, branching, acyclic digraph, chain partition, Dilworth's theorem, min-max theorem, approximation algorithm, heuristic
Published in RUP: 17.09.2018; Views: 3673; Downloads: 105
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9. Reconstructing perfect phylogenies via binary matrices, branchings in DAGs, and a generalization of Dilworth's theoremMartin Milanič, 2018, published scientific conference contribution abstract (invited lecture) Keywords: perfect phylogeny, NP-hard problem, graph coloring, branching, acyclic digraph, chain partition, Dilworth's theorem, min-max theorem, approximation algorithm, heuristic
Published in RUP: 17.09.2018; Views: 3476; Downloads: 22
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10. Perfect phylogenies via branchings in acyclic digraphs and a generalization of Dilworth's theoremAdemir Hujdurović, Edin Husić, Martin Milanič, Romeo Rizzi, Alexandru I. Tomescu, 2018, original scientific article Keywords: perfect phylogeny, minimum conflict-free row split problem, branching, acyclic digraph, chain partition, Dilworth's theorem, min-max theorem, approximation algorithm, APXhardness
Published in RUP: 08.05.2018; Views: 4178; Downloads: 162
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