15 research outputs found
Uncertain Multi-Criteria Optimization Problems
Most real-world search and optimization problems naturally involve multiple criteria as objectives. Generally, symmetry, asymmetry, and anti-symmetry are basic characteristics of binary relationships used when modeling optimization problems. Moreover, the notion of symmetry has appeared in many articles about uncertainty theories that are employed in multi-criteria problems. Different solutions may produce trade-offs (conflicting scenarios) among different objectives. A better solution with respect to one objective may compromise other objectives. There are various factors that need to be considered to address the problems in multidisciplinary research, which is critical for the overall sustainability of human development and activity. In this regard, in recent decades, decision-making theory has been the subject of intense research activities due to its wide applications in different areas. The decision-making theory approach has become an important means to provide real-time solutions to uncertainty problems. Theories such as probability theory, fuzzy set theory, type-2 fuzzy set theory, rough set, and uncertainty theory, available in the existing literature, deal with such uncertainties. Nevertheless, the uncertain multi-criteria characteristics in such problems have not yet been explored in depth, and there is much left to be achieved in this direction. Hence, different mathematical models of real-life multi-criteria optimization problems can be developed in various uncertain frameworks with special emphasis on optimization problems
A Polynomial-Time Algorithm for MCS Partial Search Order on Chordal Graphs
We study the partial search order problem (PSOP) proposed recently by
Scheffler [WG 2022]. Given a graph together with a partial order over the
vertices of , this problem determines if there is an -ordering
that is consistent with the given partial order, where is a graph
search paradigm like BFS, DFS, etc. This problem naturally generalizes the
end-vertex problem which has received much attention over the past few years.
It also generalizes the so-called -tree recognition problem
which has just been studied in the literature recently. Our main contribution
is a polynomial-time dynamic programming algorithm for the PSOP on chordal
graphs with respect to the maximum cardinality search (MCS). This resolves one
of the most intriguing open questions left in the work of Sheffler [WG 2022].
To obtain our result, we propose the notion of layer structure and study
numerous related structural properties which might be of independent interest.Comment: 12 page
Graphs with at most two moplexes
A moplex is a natural graph structure that arises when lifting Dirac's
classical theorem from chordal graphs to general graphs. However, while every
non-complete graph has at least two moplexes, little is known about structural
properties of graphs with a bounded number of moplexes. The study of these
graphs is motivated by the parallel between moplexes in general graphs and
simplicial modules in chordal graphs: Unlike in the moplex setting, properties
of chordal graphs with a bounded number of simplicial modules are well
understood. For instance, chordal graphs having at most two simplicial modules
are interval. In this work we initiate an investigation of -moplex graphs,
which are defined as graphs containing at most moplexes. Of particular
interest is the smallest nontrivial case , which forms a counterpart to
the class of interval graphs. As our main structural result, we show that the
class of connected -moplex graphs is sandwiched between the classes of
proper interval graphs and cocomparability graphs; moreover, both inclusions
are tight for hereditary classes. From a complexity theoretic viewpoint, this
leads to the natural question of whether the presence of at most two moplexes
guarantees a sufficient amount of structure to efficiently solve problems that
are known to be intractable on cocomparability graphs, but not on proper
interval graphs. We develop new reductions that answer this question negatively
for two prominent problems fitting this profile, namely Graph Isomorphism and
Max-Cut. On the other hand, we prove that every connected -moplex graph
contains a Hamiltonian path, generalising the same property of connected proper
interval graphs. Furthermore, for graphs with a higher number of moplexes, we
lift the previously known result that graphs without asteroidal triples have at
most two moplexes to the more general setting of larger asteroidal sets
Linear Time LexDFS on Chordal Graphs
Lexicographic Depth First Search (LexDFS) is a special variant of a Depth
First Search (DFS), which was introduced by Corneil and Krueger in 2008. While
this search has been used in various applications, in contrast to other graph
searches, no general linear time implementation is known to date. In 2014,
K\"ohler and Mouatadid achieved linear running time to compute some special
LexDFS orders for cocomparability graphs. In this paper, we present a linear
time implementation of LexDFS for chordal graphs. Our algorithm is able to find
any LexDFS order for this graph class. To the best of our knowledge this is the
first unrestricted linear time implementation of LexDFS on a non-trivial graph
class. In the algorithm we use a search tree computed by Lexicographic Breadth
First Search (LexBFS)
Proceedings of the 1st International Conference on Algebras, Graphs and Ordered Sets (ALGOS 2020)
International audienceOriginating in arithmetics and logic, the theory of ordered sets is now a field of combinatorics that is intimately linked to graph theory, universal algebra and multiple-valued logic, and that has a wide range of classical applications such as formal calculus, classification, decision aid and social choice.This international conference “Algebras, graphs and ordered set” (ALGOS) brings together specialists in the theory of graphs, relational structures and ordered sets, topics that are omnipresent in artificial intelligence and in knowledge discovery, and with concrete applications in biomedical sciences, security, social networks and e-learning systems. One of the goals of this event is to provide a common ground for mathematicians and computer scientists to meet, to present their latest results, and to discuss original applications in related scientific fields. On this basis, we hope for fruitful exchanges that can motivate multidisciplinary projects.The first edition of ALgebras, Graphs and Ordered Sets (ALGOS 2020) has a particular motivation, namely, an opportunity to honour Maurice Pouzet on his 75th birthday! For this reason, we have particularly welcomed submissions in areas related to Maurice’s many scientific interests:• Lattices and ordered sets• Combinatorics and graph theory• Set theory and theory of relations• Universal algebra and multiple valued logic• Applications: formal calculus, knowledge discovery, biomedical sciences, decision aid and social choice, security, social networks, web semantics..
Graph Searches and Their End Vertices
Graph search, the process of visiting vertices in a graph in a specific
order, has demonstrated magical powers in many important algorithms. But a
systematic study was only initiated by Corneil et al.~a decade ago, and only by
then we started to realize how little we understand it. Even the apparently
na\"{i}ve question "which vertex can be the last visited by a graph search
algorithm," known as the end vertex problem, turns out to be quite elusive. We
give a full picture of all maximum cardinality searches on chordal graphs,
which implies a polynomial-time algorithm for the end vertex problem of maximum
cardinality search. It is complemented by a proof of NP-completeness of the
same problem on weakly chordal graphs.
We also show linear-time algorithms for deciding end vertices of
breadth-first searches on interval graphs, and end vertices of lexicographic
depth-first searches on chordal graphs. Finally, we present -time algorithms for deciding the end vertices of breadth-first
searches, depth-first searches, maximum cardinality searches, and maximum
neighborhood searches on general graphs
On distance-preserving elimination orderings in graphs: Complexity and algorithms
International audienceFor every connected graph G, a subgraph H of G is isometric if the distance between any two vertices in H is the same in H as in G. A distance-preserving elimination ordering of G is a total ordering of its vertex-set V (G), denoted (v 1 , v 2 ,. .. , v n), such that any subgraph G i = G\(v 1 , v 2 ,. .. , v i) with 1 ≤ i < n is isometric. This kind of ordering has been introduced by Chepoi in his study on weakly modular graphs [11]. We prove that it is NP-complete to decide whether such ordering exists for a given graph — even if it has diameter at most 2. Then, we prove on the positive side that the problem of computing a distance-preserving ordering when there exists one is fixed-parameter-tractable in the treewidth. Lastly, we describe a heuristic in order to compute a distance-preserving ordering when there exists one that we compare to an exact exponential time algorithm and to an ILP formulation for the problem
Distance-preserving orderings in graphs
For every connected graph G, a subgraph H of G is isometric if the distance between any two vertices in H is the same in H as in G. A distance-preserving elimination ordering of G is a total ordering of its vertex-set V (G), denoted (v1; v2;...,vn), such that any subgraph Gi = G n (v1; v2;..., vi) with 1 ≤ i < n is isometric. This kind of ordering has been introduced by Chepoi in his study on weakly modular graphs [11]. We prove that it is NP-complete to decide whether such ordering exists for a given graph | even if it has diameter at most 2. Then, we prove on the positive side that the problem of computing a distance-preserving ordering when there exists one is fixed-parameter-tractable in the treewidth. Lastly, we describe a heuristic in order to compute a distance-preserving ordering when there exists one that we compare to an exact exponential time algorithm and to an ILP formulation for the problem.Nous étudions les ordres d’élimination des sommets préservant les distances dans les graphes
Unified View of Graph Searching and LDFS-Based Certifying Algorithms
International audienc