Sparse rank-deficient variance maximizationhttp://www.library.tuc.gr/artemis/DT2000-0057/DT2000-0057.pdfhttp://purl.tuc.gr/dl/dias/6B523CA2-8BEE-40E2-9D2D-5B6B853FEFEASparse rank-deficient variance maximizationfree2014-03-24application/pdf