We investigate three related and important problems connected to machine learning: approximating a submodular function everywhere, learning a submodular function (in a PAC-like setting [53]), and constrained minimization of submodular functions. We show that the complexity of all three problems depends on the 'curvature' of the submodular function, and provide lower and upper bounds that refine and improve previous results [3, 16, 18, 52]. Our proof techniques are fairly generic. We either use a black-box transformation of the function (for approximation and learning), or a transformation of algorithms to use an appropriate surrogate function (for minimization). Curiously, curvature has been known to influence approximations for submodular maximization [7, 55], but its effect on minimization, approximation and learning has hitherto been open. We complete this picture, and also support our theoretical claims by empirical results.

本文探究了三个相关且重要的机器学习问题。我们展示了这三个问题的复杂度都依赖于子模函数的'曲率'，并提供了改进旧有结果的上下界。我们证明了曲率对于子模函数的近似、最小化和学习有影响，并通过实验结果支持了我们的理论结论。

学习和最小化子模函数的曲率和最优算法