Gottfried Tinhofer

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A method to solve the maximum clique problem based on an unconstmin~ quadratic zero-one programming fo~ulation is presented. A branch and bound algorithm for unconstrained quadratic zero-one programming is given that uses a technique to dynamically select variables for the ordering of the branching tree. Dynamic variable selection is equivalent to vertex(More)
Two graphsG andG′ having adjacency matricesA andB are called ds-isomorphic iff there is a doubly stochastic matrixX satisfyingXA=BX.Ds-isomorphism is a relaxation of the classical isomorphism relation. In section 2 a complete set of invariants with respect tods-isomorphism is given. In the case whereA=B (ds-automorphism) the main question is: For which(More)
In this paper we introduce and investigate a new class of graphs called algebraic forests for which isomorphism testing can be done in time O(n3 log n). The class of algebraic forests admits a membership test of the same complexity, it includes cographs, trees and interval graphs, and even a joint superclass of the latter two, namely, rooted directed path(More)
This paper deals with a new method of coding unlabeled trees, the resulting code being a string of integers. For a tree onn vertices both the coding and the decoding algorithm work in time 0(n). Givenn the “mean length” of code strings is shorter than with other existing integer string codes. The new coding method is used to derive an algorithm for(More)