Mathematical Engineering
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Alain Bretto
Hypergraph Theory
An Introduction
123
Alain Bretto
Computer Science Department
Universite de Caen
Caen
France
ISSN 2192-4732
ISBN 978-3-319-00079-4
DOI 10.1007/978-3-319-00080-0
Springer Cham Heidelberg New York Dordrecht London
ISSN 2192-4740 (electronic)
ISBN 978-3-319-00080-0
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Do not worry if you have difficulties in math,
I can assure you mine are far greater
Albert Einstein
Preface
Hypergraphs are systems of finite sets and form, probably, the most general
concept in discrete mathematics. This branch of mathematics has developed very
rapidly during the latter part of the twentieth century, influenced by the advent of
computer science. Many theorems on set systems were already known at the
beginning of the twentieth century, but these results did not form a mathematical
field in itself. It was only in the early 1960s that hypergraphs become an inde-
pendent theory. Hence, hypergraph theory is a recent theory. It was mostly
developed in Hungary and France under the leadership of mathematicians like Paul
Erdös, László Lovász, Paul Turán,… but also by C. Berge, for the French school.
Originally, developed in France by Claude Berge in 1960, it is a generalization of
graph theory. The basic idea consists in considering sets as generalized edges and
then in calling hypergraph the family of these edges (hyperedges). As extension of
graphs, many results on trees, cycles, coverings, and colorings of hypergraphs will
be seen in this book.
Hypergraphs model more general types of relations than graphs do. In the past
decades, the theory of hypergraphs has proved to be of a major interest in appli-
cations to real-world problems. These mathematical tools can be used to model
networks, biology networks, data structures, process scheduling, computations and
a variety of other systems where complex relationships between the objects in the
system play a dominant role. From a theoretical point of view, hypergraphs allow
to generalize certain theorems on graphs, even to replace several theorems on
graphs by a single theorem of hypergraphs. For instance, the Berge’s weak perfect
graph conjecture, which says that a graph is perfect if and only if its complement is
perfect, was proved thanks to the concept of normal hypergraph. From a practical
point of view, they are now increasingly preferred to graphs.
In this book, we give a general and nonstandard presentation of the theory of
hypergraphs, although many paragraphs deal with the traditional elements of this
theory.
In Chap. 1, we introduce the basic language of hypergraphs. The last para-
graphs are devoted to more original concepts such as entropy of hypergraph.
Similarities and kernels are also discussed. This chapter could be useful to engi-
neers and anyone interested in applied science.
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Preface
Chapter 2 provides the first properties such as the Helly property, the König
property, and so on. Standard invariants of hypergraphs are also discussed. In
Chap. 3, the classical notions of colorings are addressed.
In the early 1980s, scientists information theory introduced decomposition-join
approaches into the design and study of databases with large size. A decomposi-
tion of a relation induces a database scheme, that is a hypergraph on the attributer
set. So tree and hypertree decompositions are introduced at the end of Chap. 4, as
well as the concept of acyclicities which are important in computer science. The
first paragraphs are devoted to specific classical hypergraphs. The last paragraph
introduces planarity.
With the emergence of information sciences and life science, the sizes of the
systems we deal with are becoming bigger and bigger. Hence Chap. 5 is devoted to
the reduction of hypergraphs. These reductions make it possible to preserve good
topological, combinatorial, and geometrical properties such as connexity, color-
ings, planarity, and so on. Thus, to solve a problem on hypergraph, we can develop
algorithms on its reduced hypergraph.
Chapter 6 deals with directed hypergraphs. We give some of their basic
properties, then we study the cycles in a directed hypergraph. We also introduce
the notion a algebraic representation of a dirhypergraph.
Chapter 7 gives some applications, not exhaustive and some prospective on
hypergraphs.
To summarize, this book can be divided into three, five, seven chapters or
levels. Three chapters represent learning, five chapters represent the knowledge of
the theory, seven chapters represent the culmination of everything the reader has
worked in the three and five levels.
Paris, December 2012
Alain Bretto
Acknowledgments
I make a point of cordially thanking all those who helped me in preparing this
book especially:
• Alain Faisant (Associate Professor to Université de Saint-Étienne),
• Francois Hennercart (Professor to Université de Saint-Étienne),
• Thierry Vallée.
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