Graph Theory

  • Instructor: Kristóf Bérczi
  • Contact: kristof.berczi@ttk.elte.hu
  • Prerequisites: Some degree of mathematical maturity is needed for this course. No prior knowledge of graph theory is required.
  • Text used:
    • R. Diestel, Graph Theory
    • A. Frank, Connections in combinatorial optimization
    • handouts

Course description: The course begins with an overview of the fundamental concepts of graph theory, followed by a detailed discussion of classical topics in both structural and algorithmic graph theory.

Topics covered (tentative):

  • Basics: Graphs, degrees, paths and cycles, independent sets, cliques, isomorphism, subgraphs, complement of a graph, trees, breadth-first search, depth-first search, applications.
  • Trees: Prüfer code, Cayley's theorem, exchange properties of spanning trees, Kruskal's algorithm, Matrix-tree Theorem.
  • Eulerian tours and Hamilton cycles: Königsberg bridges problem, Euler's theorem, Hamiltonian cycles and paths, necessary conditions, sufficient conditions (Dirac, Ore, Pósa, Chvátal).
  • Shortest paths: PERT method, Dijsktra's algorithm, Gallai's theorem.
  • Matchings in bipartite graphs: Kőnig-Hall-Frobenius theorem, Kőnig's algorithm, Egerváry's theorem and algorithm, stable matchings, Gale-Shapley algorithm.
  • Matchings in general graphs: Tutte's theorem, matchability of a subset, Petersen's theorem.
  • Colorings: Chromatic number and clique number, Mycielski's construction, Brooks' theorem, edge-chromatic number, Vizing' theorem, list colorings.
  • Flows and circulations: Hoffman's theorem, Max Flow-Min Cut Theorem, Menger's theorems, disjoint paths between terminal pairs, nowhere-zero flows, balanced orientations.
  • Planar graphs: Four Color Theorem, Euler's formula, bounding the number of edges of planar graphs, Kuratowski's theorem, graph minors, Wagner's theorem, Five Color Theorem, Schnyder labelings, drawing planar graphs on grids.
  • Higher connectivity: Highly edge- and node-connected graphs, block decompositions, ear decompositions.
  • Orientations: Degree bounds, Hakimi's lemma, Luigi's conjecture, F-avoiding orientations.
  • Partially ordered sets: Dilworth's theorems.
  • Perfect graphs: Basic examples, perfectness of comparability graphs, the Perfect Graph Theorem, the Strong Perfect Graph Theorem.