The paper focuses on the monotone submodular maximization problem with a general matroid constraint. The input consists of a monotone submodular set function f: 2^V → R+ given as a value oracle, and a matroid M = (V, I) given as an independence oracle.
The authors present a randomized (1 - 1/e - ε)-approximation algorithm that requires Õ(√rn) independence oracle and value oracle queries, where n is the number of elements in the matroid and r ≤ n is the rank of the matroid. This improves upon the previously best algorithm by Buchbinder-Feldman-Schwartz that requires Õ(r^2 + √rn) queries.
The key technical contribution is a new rounding algorithm that takes a point represented as a convex combination of t bases of a matroid and rounds it to an integral solution. The new rounding algorithm requires Õ(r^3/2 t) independence oracle queries, while the previously best rounding algorithm by Chekuri-Vondrák-Zenklusen requires O(r^2 t) independence oracle queries.
The authors achieve this improvement by using a directed cycle of arbitrary length in an auxiliary graph, instead of focusing on directed cycles of length two as in the previous algorithm. They also develop a new technique to efficiently find a directed cycle in the auxiliary graph using o(r) independence oracle queries with high probability.
By combining this new rounding algorithm with the submodular maximization algorithm by Buchbinder-Feldman-Schwartz, the authors obtain their main result - a (1 - 1/e - ε)-approximation algorithm with Õ(√rn) total oracle queries.
Na inny język
z treści źródłowej
arxiv.org
Głębsze pytania