@article{JMLR:v9:aspremont08a,
  author  = {Alexandre d'Aspremont and Francis Bach and Laurent El Ghaoui},
  title   = {Optimal Solutions for Sparse Principal Component Analysis},
  journal = {Journal of Machine Learning Research},
  year    = {2008},
  volume  = {9},
  number  = {42},
  pages   = {1269--1294},
  url     = {http://jmlr.org/papers/v9/aspremont08a.html}
}