@TECHREPORT{Bach2008d,
  author = {Bach, F. and Mairal, J. and Ponce, J.},
  title = {Convex Sparse Matrix Factorizations},
  year = {2008},
  month = dec,
  note = {arXiv:0812.1869},
  url = {http://arxiv.org/abs/0812.1869}
}