@article{JMLR:v10:kanamori09a,
  author  = {Takafumi Kanamori and Shohei Hido and Masashi Sugiyama},
  title   = {A Least-squares Approach to Direct Importance Estimation},
  journal = {Journal of Machine Learning Research},
  year    = {2009},
  volume  = {10},
  number  = {48},
  pages   = {1391--1445},
  url     = {http://jmlr.org/papers/v10/kanamori09a.html}
}