## Average Case Analysis of Dynamic Graph Algorithms


David Alberts
Institut für Informatik
Freie Universität Berlin
email: alberts@inf.fu-berlin.de
(joint work with Monika Rauch Henzinger)
Report B 95-03
März 1995

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Average Case Analysis of Dynamic Graph Algorithms We present a model for edge updates with restricted randomness in dynamic graph algorithms and a general technique for analyzing the expected running time of an update operation. This model is able to capture the average case in many applications, since (1) it allows restrictions on the set of edges which can be used for insertions and (2) the type (insertion or deletion) of each update operation is arbitrary, i.e., {\em not} random. We use our technique to analyze existing and new dynamic algorithms for the following problems: maximum cardinality matching, minimum spanning forest, connectivity, 2-edge connectivity, $k$-edge connectivity, $k$-vertex connectivity, and bipartiteness. Given a random graph $G$ with $m_0$ edges and $n$ vertices and a sequence of $l$ update operations such that the graph contains $m_i$ edges after operation $i$, the expected time for performing the updates for any $l$ is $O(l \log n + n \sum_{i=1}^{l} 1/\sqrt m_i)$ in the case of minimum spanning forests, connectivity, 2-edge connectivity, and bipartiteness. The expected time per update operation is $O(n)$ in the case of maximum matching. We also give improved bounds for $k$-edge and $k$-vertex connectivity. Additionally we give an insertions-only algorithm for maximum cardinality matching with worst-case $O(n)$ amortized time per insertion.