近似算子与斜坡损失SVM的最优性条件
Proximal Operator and Optimality Conditions for Ramp Loss SVM
摘要:
具有斜坡损失的支持向量机($L_r$ -SVM)由于斜坡损失的有界性而受到广泛关注。然而,相应的最优化问题是非凸的,所给出的Karush-Kuhn-Tucker(KKT)条件只是必要条件。为了丰富$L_r$的最优性理论,深入研究其统计性质,首先引入并分析了斜坡损失的邻近算子,然后建立了一个更强的最优性条件:P-平稳性,证明了P-平稳性是$L_r$局部极小的一阶充要条件。最后,基于P-平稳点的概念定义了$L_r$支持向量,并证明了所有$L_r$支持向量都落在支持超平面内,具有与硬间隔SVM相同的特征。
英文摘要:
Support vector machines with ramp loss (dubbed as $L_r$-SVM) have attracted wide attention due to the boundedness of ramp loss. However, the corresponding optimization problem is non-convex and the given Karush-Kuhn-Tucker (KKT) conditions are only the necessary conditions. To enrich the optimality theory of $L_r$-SVM and go deep into its statistical nature, we first introduce and analyze the proximal operator for ramp loss, and then establish a stronger optimality conditions: P-stationarity, which is proved to be the first-order necessary and sufficient conditions for local minimizer of $L_r$-SVM. Finally, we define the $L_r$ support vectors based on the concept of P-stationary point, and show that all $L_r$ support vectors fall into the support hyperplanes, which possesses the same feature as the one of hard margin SVM.
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