In this thesis we adapt fundamental parts of the Graph Minors series of Robertson and Seymour for the study of matching minors and investigate a connection to the study of directed graphs. We develope matching theoretic to established results of graph minor theory: We characterise the existence of a cross over a conformal cycle by means of a topological property. Furthermore, we develope a theory for perfect matching width, a width parameter for graphs with perfect matchings introduced by Norin. here we show that the disjoint alternating paths problem can be solved in polynomial time on graphs of bounded width. Moreover, we show that every bipartite graph with high perfect matching width must contain a large grid as a matching minor. Finally, we prove an analogue of the we known Flat Wall theorem and provide a qualitative description of all bipartite graphs which exclude a fixed matching minor. In der vorliegenden Arbeit werden fundamentale Teile des Graphminorenprojekts von Robertson und Seymour für das Studium von Matching Minoren adaptiert und Verbindungen zur Strukturtheorie gerichteter Graphen aufgezeigt. Wir entwickeln matchingtheoretische Analogien zu etablierten Resultaten des Graphminorenprojekts: Wir charakterisieren die Existenz eines Kreuzes über einem konformen Kreis mittels topologischer Eigenschaften. Weiter entwickeln wir eine Theorie zu perfekter Matchingweite, einem Weiteparameter für Graphen mit perfekten Matchings, der von Norin eingeführt wurde. Hier zeigen wir, dass das Disjunkte Alternierende Pfade Problem auf bipartiten Graphen mit beschränkter Weite in Polynomialzeit lösbar ist. Weiter zeigen wir, dass jeder bipartite Graph mit hoher perfekter Matchingweite ein großes Gitter als Matchingminor enthalten muss. Schließlich zeigen wir ein Analogon des bekannten Flat Wall Theorem und geben eine qualitative Beschreibung aller bipartiter Graphen an, die einen festen Matching Minor ausschließen.

This book constitutes the revised papers of the 45th International Workshop on Graph-Theoretic Concepts in Computer Science, WG 2019, held in Vall de Núria, Spain, in June 2019. The 29 full papers presented in this volume were carefully reviewed and selected from 87 submissions. They cover a wide range of areas, aiming at connecting theory and applications by demonstrating how graph-theoretic concepts can be applied in various areas of computer science. Another focus is on presenting recent results and on identifying and exploring promising directions of future research.

In this thesis we describe dualities in directed as well as undirected graphs based on tools such as width-parameters, obstructions and substructures. We mainly focus on directed graphs and their structure. In the context of a long open conjecture that bounds the monotonicity costs of a version of the directed cops and robber game, we introduce new width-measures based on directed separations that are closely related to DAG-width. We identify a tangle-like obstruction for which we prove a duality theorem. Johnson, Reed, Robertson, Seymour and Thomas introduced the width measure directed treewidth as a generalisation of treewidth for directed graphs. We introduce a new width measure, the cyclewidth, which is parametrically equivalent to directed treewidth. Making use of the connection between directed graphs and bipartite graphs with perfect matchings we characterise the digraphs of low cyclewidth. Generalising the seminal work by Robertson and Seymour resulting in a global structure theorem for undirected graphs, there is the goal of obtaining a structure theorem, based on directed treewidth, describing the structure of the directed graphs excluding a fixed butterfly minor. Working in this direction we present a new flat wall theorem for directed graphs which we believe to provide a better base for a directed structure theorem than the existing ones. On undirected graphs we present several results on induced subgraphs in the graphs themselves or the square graph of their linegraph. These results range from general statements about all graphs to the consideration of specific graph classes such as the one with exactly two moplexes. In der vorliegenden Arbeit beschreiben wir Dualitäten in gerichteten sowie in ungerichteten Graphen basierend auf Konzepten wie Weiteparametern, Obstruktionen und Substrukturen. Der Hauptfokus der Arbeit liegt bei gerichteten Graphen und ihrer Struktur. Im Kontext einer lange offenen Vermutung, dass die Monotoniekosten einer Variante des Räuber und Gendarm Spiels für gerichtete Graphen beschränkt sind, führen wir neue Weiteparameter ein, die auf gerichteten Separationen basieren und eng mit DAG-Weite verwandt sind. Wir identifizieren Tangle-artige Obstruktionen zu diesen Weiteparametern und beweisen die Dualität zwischen diesen beiden Konzepten. Johnson, Reed, Robertson, Seymour und Thomas haben die gerichtete Baumweite als gerichtete Verallgemeinerung der Baumweite auf ungerichteten Graphen eingeführt. Wir führen einen neuen Weiteparameter, die Cyclewidth, ein, der parametrisch equivalent zur gerichteten Baumweite ist. Unter Nutzung der Verwandtschaft von gerichteten Graphen und bipartiten Graphen mit perfekten Matchings charakterisieren wir die gerichteten Graphen mit kleiner Cyclewidth. Ein einschlagendes Ergebnis in der Graphenstrukturtheorie ist das Strukturtheorem von Robertson und Seymour. Basierend darauf gibt es Anstrengungen ein solches Strukturtheorem auch für gerichtete Graphen zu finden und dafür die gerichtete Baumweite als Grundlage zu nutzen. Dieses Theorem soll die Struktur aller gerichteten Graphen beschreiben, die einen festen gerichteten Graphen als Butterflyminoren ausschließen. In diesem Kontext beweisen wir ein neues Flat-wall-theorem für gerichtete Graphen, dass unserer Erwartung nach eine bessere Basis für ein gerichtetes Strukturtheorem bietet als die bisher betrachteten Alternativen. Auf ungerichteten Graphen präsentieren wir einige Ergebnisse bezüglich induzierten Subgraphen in gegebenen Graphen oder ihren Linegraphen. Diese Ergebnisse reichen von der Betrachtung spezifischer Graphklassen, wie den Graphen mit zwei Moplexen, bis zu Ergebnissen auf der allgemeinen Klasse aller Graphen.

This book collects the extended abstracts of the accepted contributions to EuroComb21. A similar book is published at every edition of EuroComb (every two years since 2001) collecting the most recent advances in combinatorics, graph theory, and related areas. It has a wide audience in the areas, and the papers are used and referenced broadly.

The matching problem is central to graph theory and the theory of algorithms. This book provides a comprehensive and straightforward introduction to the basic methods for designing efficient parallel algorithms for graph matching problems. Written for students at the beginning graduate level, the exposition is largely self-contained and example-driven; prerequisites have been kept to a minimum by including relevant background material. The book contains full details of several new techniques and will be of interest to researchers in computer science, operations research, discrete mathematics, and electrical engineering. The main theoretical tools are presented in three independent chapters, devoted to combinatorial tools, probabilistic tools, and algebraic tools. One of the goals of the book is to show how these three approaches can be combined to develop efficient parallel algorithms. The book represents a meeting point of interesting algorithmic techniques and opens up new algebraic and geometric areas.

Professional electronic edition, and student eBook edition (freely installable PDF with navigational links), available from diestel-graph-theory.com This standard textbook of modern graph theory, now in its sixth edition, combines the authority of a classic with the engaging freshness of style that is the hallmark of active mathematics. It covers the core material of the subject with concise yet reliably complete proofs, while offering glimpses of more advanced methods in each field by one or two deeper results, again with proofs given in full detail. The book can be used as a reliable text for an introductory course, as a graduate text, and for self-study. New in this 6th edition: Two new sections on how to apply the regularity lemma: counting lemma, removal lemma, and Szemerédi's theorem. New chapter section on chi-boundedness. Gallai's A-paths theorem. New or substantially simplified proofs of: - Lovász's perfect graph theorem - Seymour's 6-flow theorem - Turán's theorem - Tutte's theorem about flow polynomials - the Chvátal-Erdös theorem on Hamilton cycles - the tree-of-tangles theorem for graph minors (two new proofs, one canonical) - the 5-colour theorem Several new proofs of classical theorems. Many new exercises. From the reviews: “This outstanding book cannot be substituted with any other book on the present textbook market. It has every chance of becoming the standard textbook for graph theory.” Acta Scientiarum Mathematicarum "Deep, clear, wonderful. This is a serious book about the heart of graph theory. It has depth and integrity." Persi Diaconis & Ron Graham, SIAM Review “The book has received a very enthusiastic reception, which it amply deserves. A masterly elucidation of modern graph theory.” Bulletin of the Institute of Combinatorics and its Applications “Succeeds dramatically… a hell of a good book.” MAA Reviews “A highlight of the book is what is by far the best account in print of the Seymour-Robertson theory of graph minors.” Mathematika “…like listening to someone explain mathematics.” Bulletin of the AMS