scholarly journals Ordered Vertex Partitioning

2000 ◽  
Vol Vol. 4 no. 1 ◽  
Author(s):  
Ross M. Mcconnell ◽  
Jeremy P. Spinrad
Keyword(s):  
Canonical Representation ◽  
Modular Decomposition ◽  
Running Time ◽  
Dual Problems ◽  
International Audience ◽  
Transitive Orientation ◽  
Time Bounds

International audience A transitive orientation of a graph is an orientation of the edges that produces a transitive digraph. The modular decomposition of a graph is a canonical representation of all of its modules. Finding a transitive orientation and finding the modular decomposition are in some sense dual problems. In this paper, we describe a simple O(n + m \log n) algorithm that uses this duality to find both a transitive orientation and the modular decomposition. Though the running time is not optimal, this algorithm is much simpler than any previous algorithms that are not Ω (n^2). The best known time bounds for the problems are O(n+m) but they involve sophisticated techniques.

scholarly journals Partial Quicksort and Quickpartitionsort

2010 ◽  
Vol DMTCS Proceedings vol. AM,... (Proceedings) ◽  
Author(s):  
Conrado Martínez ◽  
Uwe Rösler
Keyword(s):  
Lower Bound ◽  
Time Analysis ◽  
Information Theoretic ◽  
Running Time ◽  
Running Time Analysis ◽  
International Audience

International audience Partial Quicksort sorts the $l$ smallest elements in a list of length $n$. We provide a complete running time analysis for this combination of Find and Quicksort. Further we give some optimal adapted versions, called Partition Quicksort, with an asymptotic running time $c_1l\ln l+c_2l+n+o(n)$. The constant $c_1$ can be as small as the information theoretic lower bound $\log_2 e$.

scholarly journals Modular decomposition and transitive orientation

1999 ◽  
Vol 201 (1-3) ◽  
pp. 189-241 ◽  
Author(s):  
Ross M. McConnell ◽  
Jeremy P. Spinrad
Keyword(s):  
Modular Decomposition ◽  
Transitive Orientation

scholarly journals Fast separation in a graph with an excluded minor

2005 ◽  
Vol DMTCS Proceedings vol. AE,... (Proceedings) ◽  
Author(s):  
Bruce Reed ◽  
David R. Wood
Keyword(s):  
Open Problem ◽  
Time Algorithm ◽  
Total Weight ◽  
Running Time ◽  
Fast Separation ◽  
Edge Graph ◽  
Excluded Minor ◽  
International Audience ◽  
Vertex Sets

International audience Let $G$ be an $n$-vertex $m$-edge graph with weighted vertices. A pair of vertex sets $A,B \subseteq V(G)$ is a $\frac{2}{3} - \textit{separation}$ of $\textit{order}$ $|A \cap B|$ if $A \cup B = V(G)$, there is no edge between $A \backslash B$ and $B \backslash A$, and both $A \backslash B$ and $B \backslash A$ have weight at most $\frac{2}{3}$ the total weight of $G$. Let $\ell \in \mathbb{Z}^+$ be fixed. Alon, Seymour and Thomas [$\textit{J. Amer. Math. Soc.}$ 1990] presented an algorithm that in $\mathcal{O}(n^{1/2}m)$ time, either outputs a $K_\ell$-minor of $G$, or a separation of $G$ of order $\mathcal{O}(n^{1/2})$. Whether there is a $\mathcal{O}(n+m)$ time algorithm for this theorem was left as open problem. In this paper, we obtain a $\mathcal{O}(n+m)$ time algorithm at the expense of $\mathcal{O}(n^{2/3})$ separator. Moreover, our algorithm exhibits a tradeoff between running time and the order of the separator. In particular, for any given $\epsilon \in [0,\frac{1}{2}]$, our algorithm either outputs a $K_\ell$-minor of $G$, or a separation of $G$ with order $\mathcal{O}(n^{(2-\epsilon )/3})$ in $\mathcal{O}(n^{1+\epsilon} +m)$ time.

scholarly journals A Branch-and-Reduce Algorithm for Finding a Minimum Independent Dominating Set

2012 ◽  
Vol Vol. 14 no. 1 (Graph and Algorithms) ◽  
Author(s):  
Serge Gaspers ◽  
Mathieu Liedloff
Keyword(s):  
Dominating Set ◽  
Independent Set ◽  
Time Algorithm ◽  
Worst Case ◽  
Running Time ◽  
Running Time Analysis ◽  
Np Hard Problem ◽  
International Audience ◽  
Maximal Independent Sets ◽  
Independent Dominating Set

Graphs and Algorithms International audience An independent dominating set D of a graph G = (V,E) is a subset of vertices such that every vertex in V \ D has at least one neighbor in D and D is an independent set, i.e. no two vertices of D are adjacent in G. Finding a minimum independent dominating set in a graph is an NP-hard problem. Whereas it is hard to cope with this problem using parameterized and approximation algorithms, there is a simple exact O(1.4423^n)-time algorithm solving the problem by enumerating all maximal independent sets. In this paper we improve the latter result, providing the first non trivial algorithm computing a minimum independent dominating set of a graph in time O(1.3569^n). Furthermore, we give a lower bound of \Omega(1.3247^n) on the worst-case running time of this algorithm, showing that the running time analysis is almost tight.

scholarly journals On P_4-tidy graphs

1997 ◽  
Vol Vol. 1 ◽  
Author(s):  
V. Giakoumakis ◽  
F. Roussel ◽  
H. Thuillier
Keyword(s):  
Optimization Problems ◽  
Linear Time ◽  
Hamiltonian Path ◽  
Clique Number ◽  
Stability Number ◽  
Sparse Graphs ◽  
Modular Decomposition ◽  
New Class ◽  
International Audience ◽  
Linear Algorithms

International audience We study the P_4-tidy graphs, a new class defined by Rusu [30] in order to illustrate the notion of P_4-domination in perfect graphs. This class strictly contains the P_4-extendible graphs and the P_4-lite graphs defined by Jamison & Olariu in [19] and [23] and we show that the P_4-tidy graphs and P_4-lite graphs are closely related. Note that the class of P_4-lite graphs is a class of brittle graphs strictly containing the P_4-sparse graphs defined by Hoang in [14]. McConnel & Spinrad [2] and independently Cournier & Habib [5] have shown that the modular decomposition tree of any graph is computable in linear time. For recognizing in linear time P_4-tidy graphs, we apply a method introduced by Giakoumakis in [9] and Giakoumakis & Fouquet in [6] using modular decomposition of graphs and we propose linear algorithms for optimization problems on such graphs, as clique number, stability number, chromatic number and scattering number. We show that the Hamiltonian Path Problem is linear for this class of graphs. Our study unifies and generalizes previous results of Jamison & Olariu ([18], [21], [22]), Hochstattler & Schindler[16], Jung [25] and Hochstattler & Tinhofer [15].

scholarly journals Graph Decompositions and Factorizing Permutations

2002 ◽  
Vol Vol. 5 ◽  
Author(s):  
Christian Capelle ◽  
Michel Habib ◽  
Fabien Montgolfier
Keyword(s):  
Graph Decomposition ◽  
Chordal Graphs ◽  
Decomposition Algorithms ◽  
Decomposition Tree ◽  
Modular Decomposition ◽  
Graph Decompositions ◽  
Linear Algorithm ◽  
Common Generalization ◽  
International Audience

International audience A factorizing permutation of a given graph is simply a permutation of the vertices in which all decomposition sets appear to be factors. Such a concept seems to play a central role in recent papers dealing with graph decomposition. It is applied here for modular decomposition and we propose a linear algorithm that computes the whole decomposition tree when a factorizing permutation is provided. This algorithm can be seen as a common generalization of Ma and Hsu for modular decomposition of chordal graphs and Habib, Huchard and Spinrad for inheritance graphs decomposition. It also suggests many new decomposition algorithms for various notions of graph decompositions.

scholarly journals The master ring problem

2005 ◽  
Vol DMTCS Proceedings vol. AD,... (Proceedings) ◽  
Author(s):  
Hadas Shachnai ◽  
Lisa Zhang
Keyword(s):  
Network Design ◽  
Optical Network ◽  
Practical Interest ◽  
Exact Algorithm ◽  
Running Time ◽  
Ring Problem ◽  
Optical Network Design ◽  
Naive Algorithm ◽  
International Audience ◽  
Special Case

International audience We consider the $\textit{master ring problem (MRP)}$ which often arises in optical network design. Given a network which consists of a collection of interconnected rings $R_1, \ldots, R_K$, with $n_1, \ldots, n_K$ distinct nodes, respectively, we need to find an ordering of the nodes in the network that respects the ordering of every individual ring, if one exists. Our main result is an exact algorithm for MRP whose running time approaches $Q \cdot \prod_{k=1}^K (n_k/ \sqrt{2})$ for some polynomial $Q$, as the $n_k$ values become large. For the $\textit{ring clearance problem}$, a special case of practical interest, our algorithm achieves this running time for rings of $\textit{any}$ size $n_k \geq 2$. This yields the first nontrivial improvement, by factor of $(2 \sqrt{2})^K \approx (2.82)^K$, over the running time of the naive algorithm, which exhaustively enumerates all $\prod_{k=1}^K (2n_k)$ possible solutions.

scholarly journals A Parameterized Measure-and-ConquerAnalysis for Finding a k-Leaf Spanning Treein an Undirected Graph

2014 ◽  
Vol Vol. 16 no. 1 (Discrete Algorithms) ◽  
Author(s):  
Daniel Binkele-Raible ◽  
Henning Fernau
Keyword(s):  
Spanning Tree ◽  
Undirected Graph ◽  
Standard Measure ◽  
Algorithm Analysis ◽  
Np Hard ◽  
Running Time ◽  
Discrete Algorithms ◽  
Parameterized Algorithmics ◽  
International Audience ◽  
Number Of Leaves

Discrete Algorithms International audience The problem of finding a spanning tree in an undirected graph with a maximum number of leaves is known to be NP-hard. We present an algorithm which finds a spanning tree with at least k leaves in time O*(3.4575k) which improves the currently best algorithm. The estimation of the running time is done by using a non-standard measure. The present paper is one of the still few examples that employ the Measure & Conquer paradigm of algorithm analysis in the area of Parameterized Algorithmics.

scholarly journals The analysis of find and versions of it

2012 ◽  
Vol Vol. 14 no. 2 (Analysis of Algorithms) ◽  
Author(s):  
Diether Knof ◽  
Uwe Roesler
Keyword(s):  
Branching Process ◽  
Analysis Of Algorithms ◽  
Time Analysis ◽  
Running Time ◽  
Random Time Change ◽  
Running Time Analysis ◽  
Finite Dimensional ◽  
Exponential Moments ◽  
International Audience ◽  
Point Measure

Analysis of Algorithms International audience In the running time analysis of the algorithm Find and versions of it appear as limiting distributions solutions of stochastic fixed points equation of the form X D = Sigma(i) AiXi o Bi + C on the space D of cadlag functions. The distribution of the D-valued process X is invariant by some random linear affine transformation of space and random time change. We show the existence of solutions in some generality via the Weighted Branching Process. Finite exponential moments are connected to stochastic fixed point of supremum type X D = sup(i) (A(i)X(i) + C-i) on the positive reals. Specifically we present a running time analysis of m-median and adapted versions of Find. The finite dimensional distributions converge in L-1 and are continuous in the cylinder coordinates. We present the optimal adapted version in the sense of low asymptotic average number of comparisons. The limit distribution of the optimal adapted version of Find is a point measure on the function [0, 1] there exists t -> 1 + mint, 1 - t.

scholarly journals An expected polynomial time algorithm for coloring 2-colorable 3-graphs

2011 ◽  
Vol Vol. 13 no. 2 (Graph and Algorithms) ◽  
Author(s):  
Yury Person ◽  
Mathias Schacht
Keyword(s):  
Polynomial Time ◽  
Polynomial Time Algorithm ◽  
Time Algorithm ◽  
Running Time ◽  
Uniform Hypergraphs ◽  
Average Running Time ◽  
International Audience

Graphs and Algorithms International audience We present an algorithm that for 2-colorable 3-uniform hypergraphs, finds a 2-coloring in average running time O (n(5) log(2) n).

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