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Low Rank Representation – Theories and Applications(ppt详解).pdf

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Low Rank Representation – Theories and Applications 林宙辰 北京大学 April 13, 2012 ¼
Outline • Low Rank Representation • Some Theoretical Analysis • Applications • Generalizations ¼minrank(A);s:t:D=¼(A):
Sparse Subspace Clustering • Sparse Representation • Sparse Subspace Clustering Elhamifar and Vidal. Sparse Subspace Clustering. CVPR2009. minjjxjj0;s:t:y=Ax:(1)minjjzijj0;s:t:xi=X^izi;8i:(2)whereX^i=[x1;¢¢¢;xi¡1;xi+1;¢¢¢;xn].minjjZjj0;s:t:X=XZ;diag(Z)=0:(3)minjjZjj1;s:t:X=XZ;diag(Z)=0:(4)
Sparse Subspace Clustering • Construct a graph • Normalized cut on the graph Elhamifar and Vidal. Sparse Subspace Clustering. CVPR2009. W=(jZ¤j+j(Z¤)Tj)=2
Sparse Subspace Clustering Elhamifar and Vidal. Sparse Subspace Clustering. CVPR2009. Theorem.Assumethedataiscleanandisdrawnfromindependentsubspaces,thenZ¤isblockdiagonal.dim(PiSi)=Pidim(Si):
Drawback of SSC • Sensitive to noise: no cross validation among coefficients Elhamifar and Vidal. Sparse Subspace Clustering. CVPR2009. minjjzijj1;s:t:xi=Xzi;(zi)i=0:(5)minjjZjj1;s:t:X=XZ;diag(Z)=0:(4)
Hints from 2D Sparsity • Rank is a good measure of 2D sparsity – Real data usually lie on low-dim manifolds > 1B dim low-dim subspaces → low rank data matrices – Low rank ↔ high correlation among rows/columns
Low Rank Representation no additional constraint! Liu, Lin, and Yu. Robust Subspace Segmentation by Low-Rank Representation, ICML 2010. minjjZjj1;s:t:X=XZ;diag(Z)=0:(4)minjjZjj¤;s:t:X=XZ:(6)jjZjj¤=Pj¾j(Z),nuclearnorm,aconvexsurrogateofrank.
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