|
|
Computational complexity in graph theory
Melka, Jakub ; Kratochvíl, Jan (advisor) ; Fiala, Jiří (referee)
In the present work we study the problem of reconstructing a graph from its closed neighbourhood list. We will explore this problem, formulated by V. Sós, from the point of view of the fixed parameter complexity. We study the graph reconstruction problem in a more general setting, when the reconstructed graph is required to belong to some special graph class. In the present work we prove that this general problem lies in the complexity class FPT, when parametrized by the treewidth and maximum degree of the reconstructed graph, or by the number of certain special induced subgraphs if the reconstructed graph is 2-degenerate. Also, we prove that the graph reconstruction problem lies in the complexity class XP when parametrized by the vertex cover number. Finally, we prove mutual independence of the results
|
|
|
Immersions and edge-disjoint linkages
Klimošová, Tereza ; Dvořák, Zdeněk (advisor) ; Kráľ, Daniel (referee)
Graph immersions are a natural counterpart to the widely studied concepts of graph minors and topological graph minors, and yet their theory is much less developed. In the present work we search for sufficient conditions for the existence of the immersions and the properties of the graphs avoiding an immersion of a fixed graph. We prove that large tree-with of 4-edge-connected graph implies the existence of immersion of any 4-regular graph on small number of vertices and that large maximum degree of 3-edge-connected graph implies existence of immersion of any 3-regular graph on small number of vertices.
|
|
|
Optimization in graphs with bounded treewidth
Koutecký, Martin ; Kolman, Petr (advisor) ; Kráľ, Daniel (referee)
Courcelle's theorem speaks about computational complexity of decision problems defined by formulae in monadic second order logic over relational structures with bounded treewodth. For a fixed treewidth and a fixed formula, Courcelle's theorem gives an algorithm, which decides the formula over a structure of said treewidth in linear time. is thesis provides a self-contained proof of Courcelle's theorem using methods of finite model theory. Furthermore it contains the proofs of all propositions and theorems upon which the main proof depends, notably the Ehrenfeucht-Fraïssé theorem widely used in finite model theory. e thesis also contains an implementa- tion of an algorithm which follows from the main proof. Finally a sketch of the current state of the art of the area of research is given, as well as the possibilities following from it. 1
|
|
|
Length bounded cuts in graphs
Berg, Michal ; Kolman, Petr (advisor) ; Dvořák, Pavel (referee)
In this thesis we will focus on a problem of length bounded cut, also known as L-bounded cut. We are going to show a combinatorial algorithm for finding a minimal L-bounded cut on graphs with bounded treewidth based on dynamic programming. Then we going to show that this algorithm can also be used for finding minimal L-bounded cut on plannar graphs. We are also going to look at problem of (dG(s, t) + 1)-bounded cut. This problem is known to be NP-hard for general graphs. But it is an open problem whether this problem is also NP-hard on plannar graphs with special vertices on the outer face. We will try to outline a way, which might lead to showing that this problem is solvable in a polynomial time.
|
|
|
Treewidth, Extended Formulations of CSP and MSO Polytopes, and their Algorithmic Applications
Koutecký, Martin ; Kolman, Petr (advisor) ; Fellows, Michael R. (referee) ; Tantau, Till (referee)
In the present thesis we provide compact extended formulations for a wide range of polytopes associated with the constraint satisfaction problem (CSP), monadic second order logic (MSO) on graphs, and extensions of MSO, when the given instances have bounded treewidth. We show that our extended formulations have additional useful properties, and we uncover connections between MSO and CSP. We conclude that a combination of the MSO logic, CSP and geometry provides an extensible framework for the design of compact extended formulations and parameterized algorithms for graphs of bounded treewidth. Putting our framework to use, we settle the parameterized complexity landscape for various extensions of MSO when parameterized by two important graph width parameters, namely treewidth and neighborhood diversity. We discover that the (non)linearity of the MSO extension determines the difference between fixedparameter tractability and intractability when parameterized by neighborhood diversity. Finally, we study shifted combinatorial optimization, a new nonlinear optimization framework generalizing standard combinatorial optimization, and provide initial findings from the perspective of parameterized complexity
|
|
|
Parity vertex colorings
Soukup, Jan ; Gregor, Petr (advisor) ; Kučera, Petr (referee)
A parity path in a vertex colouring of a graph G is a path in which every colour is used even number of times. A parity vertex colouring is a vertex colouring having no parity path. Let χp(G) be the minimal number of colours in a parity vertex colouring of G. It is known that χp(Bn) ≥ √ n where Bn is the complete binary tree with n layers. We show that the sharp inequality holds. We use this result to obtain a new bound χp(T) > 3 √ log n where T is any binary tree with n vertices. We study the complexity of computing the parity chromatic number χp(G). We show that checking whether a vertex colouring is a parity vertex colouring is coNP-complete and we design an exponential algorithm to com- pute it. Then we use Courcelle's theorem to prove the existence of a FPT algorithm checking whether χp(G) ≤ k parametrized by k and the treewidth of G. Moreover, we design our own FPT algorithm solving the problem. This algorithm runs in polynomial time whenever k and the treewidth of G is bounded. Finally, we discuss the relation of this colouring to other types of colourings, specifically unique maximum, conflict free, and parity edge colourings.
|
|
|
Computational complexity in graph theory
Melka, Jakub ; Kratochvíl, Jan (advisor) ; Fiala, Jiří (referee)
In the present work we study the problem of reconstructing a graph from its closed neighbourhood list. We will explore this problem, formulated by V. Sós, from the point of view of the fixed parameter complexity. We study the graph reconstruction problem in a more general setting, when the reconstructed graph is required to belong to some special graph class. In the present work we prove that this general problem lies in the complexity class FPT, when parametrized by the treewidth and maximum degree of the reconstructed graph, or by the number of certain special induced subgraphs if the reconstructed graph is 2-degenerate. Also, we prove that the graph reconstruction problem lies in the complexity class XP when parametrized by the vertex cover number. Finally, we prove mutual independence of the results
|
|
|
Immersions and edge-disjoint linkages
Klimošová, Tereza ; Dvořák, Zdeněk (advisor) ; Kráľ, Daniel (referee)
Graph immersions are a natural counterpart to the widely studied concepts of graph minors and topological graph minors, and yet their theory is much less developed. In the present work we search for sufficient conditions for the existence of the immersions and the properties of the graphs avoiding an immersion of a fixed graph. We prove that large tree-with of 4-edge-connected graph implies the existence of immersion of any 4-regular graph on small number of vertices and that large maximum degree of 3-edge-connected graph implies existence of immersion of any 3-regular graph on small number of vertices.
|
|
|
Optimization in graphs with bounded treewidth
Koutecký, Martin ; Kolman, Petr (advisor) ; Kráľ, Daniel (referee)
Courcelle's theorem speaks about computational complexity of decision problems defined by formulae in monadic second order logic over relational structures with bounded treewodth. For a fixed treewidth and a fixed formula, Courcelle's theorem gives an algorithm, which decides the formula over a structure of said treewidth in linear time. is thesis provides a self-contained proof of Courcelle's theorem using methods of finite model theory. Furthermore it contains the proofs of all propositions and theorems upon which the main proof depends, notably the Ehrenfeucht-Fraïssé theorem widely used in finite model theory. e thesis also contains an implementa- tion of an algorithm which follows from the main proof. Finally a sketch of the current state of the art of the area of research is given, as well as the possibilities following from it. 1
|
guest ::
