, Volume 75, Issue 4, pp 579–605 | Cite as

An Asymptotic Analysis of Labeled and Unlabeled k-Trees



In this paper we provide a systematic treatment of several shape parameters of (random) k-trees. Our research is motivated by many important algorithmic applications of k-trees in the context of tree-decomposition of a graph and graphs of bounded tree-width. On the other hand, k-trees are also a very interesting object from the combinatorial point of view. For both labeled and unlabeled k-trees, we prove that the number of leaves and more generally the number of nodes of given degree satisfy a central limit theorem with mean value and variance that are asymptotically linear in the size of the k-tree. In particular we solve the asymptotic counting problem for unlabeled k-trees. By applying a proper singularity analysis of generating functions we show that the numbers \(U_k(n)\) of unlabeled k-trees of size n are asymptotically given by \(U_k(n) \sim c_k n^{-5/2}\rho _{k}^{-n}\), where \(c_k> 0\) and \(\rho _{k}>0\) denotes the radius of convergence of the generating function \(U(z)=\sum _{n\ge 0} U_k(n) z^n\).


k-trees Generating function Singularity analysis  Central limit theorem 

Mathematics Subject Classification

05A16 05A15 



We thank the anonymous reviewers for helpful suggestions on the first version of this paper.


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Copyright information

© Springer Science+Business Media New York 2015

Authors and Affiliations

  1. 1.Institut für Diskrete Mathematik und GeometrieTU WienViennaAustria

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