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arXiv 1306.1866math.STstat.TH
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凸函数在极大范数下的Minimax最优估计

Minimax Optimal Estimation of Convex Functions in the Supreme Norm

Teresa M. Lebair, Jinglai Shen, Xiao Wang

摘要:

凸函数的估计在工程和科学中有着广泛的应用,而凸形状约束在渐近性能分析中引起了许多挑战。本文在形状约束非参数估计的框架下,研究了Hölder类一元凸函数的Minimax最优估计.特别地,本文建立了Hölder阶在1和2之间的凸函数的极大极小超模风险的两步最优收敛速率.第一步,应用信息论关于概率测度距离的结果,通过构造一类新的Hölder类分段二次凸函数,得到了极大极小下界.在第二步中,我们提出了一个惩罚凸样条估计,并建立了极大极小上界。由于凸形状约束,惩罚凸样条的最优性条件由非光滑互补条件刻画。利用互补方法,建立了最优样条系数在无穷范数下的一致Lipschitz性质。这个属性,以及渐近估计技术,导致在整个区间上的偏差和随机误差的统一界限。通过选择合适的节点数和惩罚值,进一步产生最佳的收敛收敛速率。给出了最大范数下凸估计的最优极小极大风险的第一个严格证明。

英文摘要:

Estimation of convex functions finds broad applications in engineering and science, while convex shape constraint gives rise to numerous challenges in asymptotic performance analysis. This paper is devoted to minimax optimal estimation of univariate convex functions from the Hölder class in the framework of shape constrained nonparametric estimation. Particularly, the paper establishes the optimal rate of convergence in two steps for the minimax sup-norm risk of convex functions with the Hölder order between one and two. In the first step, by applying information theoretical results on probability measure distance, we establish the minimax lower bound under the supreme norm by constructing a novel family of piecewise quadratic convex functions in the Hölder class. In the second step, we develop a penalized convex spline estimator and establish the minimax upper bound under the supreme norm. Due to the convex shape constraint, the optimality conditions of penalized convex splines are characterized by nonsmooth complementarity conditions. By exploiting complementarity methods, a critical uniform Lipschitz property of optimal spline coefficients in the infinity norm is established. This property, along with asymptotic estimation techniques, leads to uniform bounds for bias and stochastic errors on the entire interval of interest. This further yields the optimal rate of convergence by choosing the suitable number of knots and penalty value. The present paper provides the first rigorous justification of the optimal minimax risk for convex estimation under the supreme norm.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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