说明：  线性图嵌入方法，该方法是一种基于图框架的子空间学习方法，被用于LPP,NPE等流行学习方法中。
((Regularized) Linear Graph Embedding (Provides a general framework for graph based subspace learning. This function will be called by LPP, NPE, IsoProjection, LSDA, MMP ...) )