Now showing items 1-20 of 26

• #### Approximating Acyclicity Parameters of Sparse Hypergraphs ﻿

(Conference object; Peer reviewed; Journal article, 2009)
The notions of hypertree width and generalized hypertree width were introduced by Gottlob, Leone, and Scarcello (PODS'99, PODS'01) in order to extend the concept of hypergraph acyclicity. These notions were further generalized ...
• #### Connecting Vertices by Independent Trees ﻿

(Conference object, 2014)
We study the paramereteized complexity of the following connectivity problem. For a vertex subset U of a graph G, trees T1, . . . , Ts of G are completely independent spanning trees of U if each of them contains U , and ...
• #### Covering Vectors by Spaces in Perturbed Graphic Matroids and Their Duals ﻿

(Peer reviewed; Journal article, 2019)
Perturbed graphic matroids are binary matroids that can be obtained from a graphic matroid by adding a noise of small rank. More precisely, an r-rank perturbed graphic matroid M is a binary matroid that can be represented ...
• #### Decomposition of map graphs with applications ﻿

(Peer reviewed; Journal article, 2019)
• #### Exact algorithms for treewidth and minimum fill-in ﻿

(Journal article, 2006)
• #### Exploring Subexponential Parameterized Complexity of Completion Problems ﻿

(Peer reviewed; Journal article, 2014-02-19)
Let F be a family of graphs. In the F-Completion problem, we are given an n-vertex graph G and an integer k as input, and asked whether at most k edges can be added to G so that the resulting graph does not contain a graph ...
• #### Finding Induced Subgraphs via Minimal Triangulations ﻿

(Conference object; Peer reviewed; Journal article, 2010)
Potential maximal cliques and minimal separators are combinatorial objects which were introduced and studied in the realm of minimal triangulation problems in- cluding Minimum Fill-in and Treewidth. We discover unexpected ...
• #### A Fixed-Parameter Perspective on #BIS ﻿

(Peer reviewed; Journal article, 2019-07-18)
The problem of (approximately) counting the independent sets of a bipartite graph (#BIS) is the canonical approximate counting problem that is complete in the intermediate complexity class #RHΠ1. It is believed that #BIS ...
• #### Going Far From Degeneracy ﻿

(Peer reviewed; Journal article, 2019-09-06)
An undirected graph G is d-degenerate if every subgraph of G has a vertex of degree at most d. By the classical theorem of Erd\H{o}s and Gallai from 1959, every graph of degeneracy d>1 contains a cycle of length at least ...
• #### Kernel(s) for Problems with No Kernel: On Out-Trees with Many Leaves ﻿

(Conference object; Peer reviewed; Journal article, 2009)
The {\sc $k$-Leaf Out-Branching} problem is to find an out-branching, that is a rooted oriented spanning tree, with at least $k$ leaves in a given digraph. The problem has recently received much attention from the ...
• #### Largest chordal and interval subgraphs faster than 2n ﻿

(Peer reviewed; Journal article, 2015-08-22)
We prove that in a graph with n vertices, induced chordal and interval subgraphs with the maximum number of vertices can be found in time O(2λn) for some λ< 1. These are the first algorithms breaking the trivial 2nnO(1) ...
• #### Minimum Fill-in of Sparse Graphs: Kernelization and Approximation ﻿

(Conference object; Peer reviewed; Journal article, 2011)
The Minimum Fill-in problem is to decide if a graph can be triangulated by adding at most k edges. The problem has important applications in numerical algebra, in particular in sparse matrix computations. We develop ...
• #### Modification to planarity is fixed parameter tractable ﻿

(Peer reviewed; Journal article, 2019)
A replacement action is a function L that maps each k-vertex labeled graph to another k-vertex graph. We consider a general family of graph modification problems, called L-Replacement to C, where the input is a graph G and ...
• #### A Note on Exact Algorithms for Vertex Ordering Problems on Graphs ﻿

(Peer reviewed; Journal article, 2011-01-21)
In this note, we give a proof that several vertex ordering problems can be solved in O ∗(2 n ) time and O ∗(2 n ) space, or in O ∗(4 n ) time and polynomial space. The algorithms generalize algorithms for the Travelling ...
• #### On width measures and topological problems on semi-complete digraphs ﻿

(Peer reviewed; Journal article, 2019)
The topological theory for semi-complete digraphs, pioneered by Chudnovsky, Fradkin, Kim, Scott, and Seymour [10], [11], [12], [28], [43], [39], concentrates on the interplay between the most important width measures — ...
• #### Parameterized complexity of secluded connectivity problems ﻿

(Conference object; Peer reviewed; Journal article, 2015)
The Secluded Path problem introduced by Chechik et al. in [ESA 2013] models a situation where a sensitive information has to be transmitted between a pair of nodes along a path in a network. The measure of the quality of ...
• #### Parameterized complexity of the spanning tree congestion problem ﻿

(Peer reviewed; Journal article, 2012-09)
We study the problem of determining the spanning tree congestion of a graph. We present some sharp contrasts in the parameterized complexity of this problem. First, we show that on apex-minor-free graphs, a general class ...
• #### Parameterized k-Clustering: Tractability Island ﻿

(Peer reviewed; Journal article, 2019)
In k-Clustering we are given a multiset of n vectors X subset Z^d and a nonnegative number D, and we need to decide whether X can be partitioned into k clusters C_1, ..., C_k such that the cost sum_{i=1}^k min_{c_i in R^d} ...
• #### Parameterized Single-Exponential Time Polynomial Space Algorithm for Steiner Tree ﻿

(Peer reviewed; Journal article, 2019)
In the Steiner Tree problem, we are given as input a connected $n$-vertex graph with edge weights in $\{1,2,\ldots,W\}$, and a set of $k$ terminal vertices. Our task is to compute a minimum-weight tree that contains ...
• #### Path Contraction Faster Than 2n ﻿

(Peer reviewed; Journal article, 2019)
A graph G is contractible to a graph H if there is a set X subseteq E(G), such that G/X is isomorphic to H. Here, G/X is the graph obtained from G by contracting all the edges in X. For a family of graphs F, the F-Contraction ...