摘要
基于图的半监督分类是近年来机器学习与数据挖掘领域的研究热点之一.该类方法一般通过构造图来挖掘数据中所蕴含的本质结构,并进一步利用图的结构信息帮助对无标签样本进行分类.一般来说,基于图的半监督分类方法的效果高度依赖于其构造的图.本文提出了一种基于仿射子空间稀疏表示的图构造方法,该稀疏编码方法在最小化输入信号重构误差时考虑了3个约束条件:(1)输入信号能够被字典矩阵的仿射组合近似表示;(2)线性表示系数的非负性约束;(3)线性表示系数的稀疏性约束.根据这3个约束,我们构造了基于l0-范数的稀疏编码的约束优化问题,提出相应近似求解方法,并进而构造了数据的l0-图.最后,在正则化学习理论框架下,通过引进度量l0-图中结构保持误差的正则项,提出了一种新的半监督学习方法.该方法具有显性的多类分类函数,同时也继承了由数据稀疏编码所得l0-图中蕴含的强判别信息,因此对外样本具有快速和准确的分类能力.一系列人工数据与现实采集的数据集上的实验结果验证了所提半监督分类方法的有效性.
Graph-based semi-supervised classification is one of the hottest research areas in machine learning and data mining. These methods usually model an entire dataset as a graph, then utilize the structure information extracted by the graph to help with the classification of unlabeled data. Generally speaking, the performance of graph-based semi-supervised classification methods highly depends on the constructed graphs. In this paper, we propose a new kind of graph construction method based on affine subspace sparse representation. The proposed sparse coding method minimizes the construction error of the input signal, considering three constraints:(1) the input signal being approximately reconstructed by the affine combination of the dictionary;(2) the nonnegativity constraint of the reconstruction coefficients;(3) the sparsity constraint of the reconstruction coefficients. Based on the constraints, we present the l0-norm constrained optimization problem for sparse coding; then, we propose the algorithm to solve the problem and further construct the l0-graph of data. Finally, under the manifold regularization framework, we propose a new kind of semi-supervised classification method by introducing the regularization term that measures the structure preserving error of the l0-graph. The proposed semi-supervised classification method has an explicit multiclass classification function and inherits the strong discriminative information from sparse representation. As a result, it has efficient and effective classification ability. Experimental results on artificial and real-world datasets are provided to show the effectiveness of the proposed method.
引文
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