On the complexity of finding a sun in a graph

Finding a sun in building-free graphs

Deciding whether an arbitrary graph contains a sun was recently shown to be NP-complete. We show that whether a building-free graph contains a sun can be decided in O(min$\{m{n^3}, m^{1.5}n^2\}$) time and, if a sun exists, it can be found in the same time bound. The class of building-free graphs contains many interesting classes of perfect graphs such as Meyniel graphs which, in turn, contains classes such as hhd-free graphs, i-triangulated graphs, and parity graphs. Moreover, there are imperfect graphs that are building-free. The class of building-free graphs generalizes several classes of gr…

On the complexity of finding gapped motifs

This paper has been withdrawn by the corresponding author because the newest version is now published in Journal of Discrete Algorithms.

On the complexity of finding well-balanced orientations with upper bounds on the out-degrees

We show that the problem of deciding whether a given graph $G$ has a well-balanced orientation $\vec{G}$ such that $d_{\vec{G}}^+(v)\leq \ell(v)$ for all $v \in V(G)$ for a given function $\ell:V(G)\rightarrow \mathbb{Z}_{\geq 0}$ is NP-complete. We also prove a similar result for best-balanced orientations. This improves a result of Bern\' ath, Iwata, Kir\' aly, Király and Szigeti and answers a question of Frank.

The parameterized complexity of finding secluded solutions to some classical optimization problems on graphs

This work studies the parameterized complexity of finding secluded solutions to classical combinatorial optimization problems on graphs such as finding minimum s-t separators, feedback vertex sets, dominating sets, maximum independent sets, and vertex deletion problems for hereditary graph properties: Herein, one searches not only to minimize or maximize the size of the solution, but also to minimize the size of its neighborhood. This restriction has applications in secure routing and community detection.

On the Complexity of Newman's Community Finding Approach for Biological and Social Networks

Given a graph of interactions, a module (also called a community or cluster) is a subset of nodes whose fitness is a function of the statistical significance of the pairwise interactions of nodes in the module. The topic of this paper is a model-based community finding approach, commonly referred to as modularity clustering, that was originally proposed by Newman and has subsequently been extremely popular in practice. Various heuristic methods are currently employed for finding the optimal solution. However, the exact computational complexity of this approach is still largely unknown. To this…

关于在无桥三次图中寻找良分布完美匹配的时间复杂度

On the time complexity of finding a well-spread perfect matching in bridgeless cubic graphs

本文提出一种O(n log^4 n)时间算法，用于在3-边连通三次图中寻找与每个3-边割恰好交于一条边的完美匹配，并应用于奇异边受限的图嵌入计算，支持Cycle Double Cover猜想研究。