Detecting cycles in dynamic graphs in polynomial time

Abstract
Consider a digraph which has labels on its edges which are k-dimensional vectors. In this paper we show it is possible in polynomial time to determine if such a digraph contains a zero cycle, i.e., a cycle whose edge labels sum to the zero vector component-wise. This solves the open problem of finding cycles in dynamic graphs which was posed by Iwano and Steiglitz. Our solution has a time complexity of &Ogr;(|V| log(|V|)Z) where Z is the complexity of a linear programming problem. For the important cases of two and three dimensions we present &Ogr;(Z) time algorithms. The linear programming problems we solve have at most 2|E| variables and &Ogr;(|E| + |V| + k) constraints.

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