Dynamic Matroids: Base Packing and Covering

In this paper, we consider dynamic matroids, where elements can be inserted to or deleted from the ground set over time. The independent sets change to reflect the current ground set. As matroids are central to the study of many combinatorial optimization problems, it is a natural next step to also consider them in a dynamic setting. The study of dynamic matroids has the potential to generalize several dynamic graph problems, including, but not limited to, arboricity and maximum bipartite matching. We contribute by providing efficient algorithms for some fundamental matroid questions. In particular, we study the most basic question of maintaining a base dynamically, providing an essential building block for future algorithms. We further utilize this result and consider the elementary problems of base packing and base covering. We provide a deterministic algorithm that maintains a (1± varepsilon)-approximation of the base packing number Phi in O(Phi · poly(log n, varepsilon-1)) queries per update. Similarly, we provide a deterministic algorithm that maintains a (1± varepsilon)-approximation of the base covering number β in O(β · poly(log n, varepsilon-1)) queries per update. Moreover, we give an algorithm that maintains a (1± varepsilon)-approximation of the base covering number β in O(poly(log n, varepsilon-1)) queries per update against an oblivious adversary. These results are obtained by exploring the relationship between base collections, a generalization of tree-packings, and base packing and covering respectively. We provide structural theorems to formalize these connections, and show how they lead to simple dynamic algorithms.