MATHIESON, LUKE (2009) *The Parameterized Complexity of Degree Constrained Editing Problems.* Doctoral thesis, Durham University.

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## Abstract

This thesis examines degree constrained editing problems within the framework of parameterized complexity. A degree constrained editing problem takes as input a graph and a set of constraints and asks whether the graph can be altered in at most k editing steps such that the degrees of the remaining vertices are within the given constraints. Parameterized complexity gives a framework for examining

problems that are traditionally considered intractable and developing efficient exact algorithms for them, or showing that it is unlikely that they have such algorithms, by introducing an additional component to the input, the parameter, which gives additional information about the structure of the problem. If the problem has an algorithm that is exponential in the parameter, but polynomial, with constant degree, in the size of the input, then it is considered to be fixed-parameter tractable.

Parameterized complexity also provides an intractability framework for identifying problems that are likely to not have such an algorithm.

Degree constrained editing problems provide natural parameterizations in terms of the total cost k of vertex deletions, edge deletions and edge additions allowed, and

the upper bound r on the degree of the vertices remaining after editing. We define a class of degree constrained editing problems, WDCE, which generalises several well know problems, such as Degree r Deletion, Cubic Subgraph, r-Regular Subgraph, f-Factor and General Factor. We show that in general if both k and r are part of the parameter, problems in the WDCE class are fixed-parameter tractable, and if parameterized by k or r alone, the problems are intractable in a parameterized sense.

We further show cases of WDCE that have polynomial time kernelizations, and in particular when all the degree constraints are a single number and the editing

operations include vertex deletion and edge deletion we show that there is a kernel with at most O(kr(k + r)) vertices. If we allow vertex deletion and edge addition,

we show that despite remaining fixed-parameter tractable when parameterized by k and r together, the problems are unlikely to have polynomial sized kernelizations, or

polynomial time kernelizations of a certain form, under certain complexity theoretic assumptions.

We also examine a more general case where given an input graph the question is whether with at most k deletions the graph can be made r-degenerate. We show that in this case the problems are intractable, even when r is a constant.

Item Type: | Thesis (Doctoral) |
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Award: | Doctor of Philosophy |

Keywords: | Theoretical Computer Science; Complexity Theory, Parameterized Complexity; Graph Algorithms; Combinatorial Graph Problems |

Faculty and Department: | Faculty of Science > Engineering and Computing Science, School of |

Thesis Date: | 2009 |

Copyright: | Copyright of this thesis is held by the author |

Deposited On: | 04 Jan 2010 15:31 |