Algorithms for Approximate Minimization of the Difference Between Submodular Functions, with Applications
This addresses a computational bottleneck in optimization for machine learning problems, but it is incremental as it builds directly on existing methods.
The paper tackles the problem of minimizing the difference between submodular functions, extending prior work by developing algorithms that reduce the objective monotonically with lower per-iteration cost and handling combinatorial constraints, and shows applications in machine learning like feature selection.
We extend the work of Narasimhan and Bilmes [30] for minimizing set functions representable as a difference between submodular functions. Similar to [30], our new algorithms are guaranteed to monotonically reduce the objective function at every step. We empirically and theoretically show that the per-iteration cost of our algorithms is much less than [30], and our algorithms can be used to efficiently minimize a difference between submodular functions under various combinatorial constraints, a problem not previously addressed. We provide computational bounds and a hardness result on the mul- tiplicative inapproximability of minimizing the difference between submodular functions. We show, however, that it is possible to give worst-case additive bounds by providing a polynomial time computable lower-bound on the minima. Finally we show how a number of machine learning problems can be modeled as minimizing the difference between submodular functions. We experimentally show the validity of our algorithms by testing them on the problem of feature selection with submodular cost features.