A General Framework for Dynamic Consistent Submodular Maximization

Consistency is an important property in dynamic submodular maximization and entails maintaining a near-optimal solution at all times, making only a small number of adjustments to the solution in each step. Prior work has explored this question for the insertion-only case, where the algorithm faces a stream of $n$ insertions, and has established lower and upper bounds for the cardinality-constrained version of the problem. We consider this question in the fully dynamic setting, where the stream of operations may contain both insertions and deletions. We develop a general framework for designing algorithms for this setting, and instantiate it to obtain the first constant-factor approximations with sublinear consistency. For cardinality constraints, we propose a $\tfrac 12 - O(\varepsilon)$ approximation that is $O\left(\tfrac{1}{\varepsilon^2}\right)$ consistent. For rank-$k$ matroid constraints, we construct a $\tfrac 14 - O(\varepsilon)$ approximation to the dynamic optimum that is $O\left(\tfrac{\log k}{\varepsilon^2}\right)$ consistent.