@article{JMLR:v12:mes11a,
  author  = {Martijn R.K. Mes and Warren B. Powell and Peter I. Frazier},
  title   = {Hierarchical Knowledge Gradient for Sequential Sampling},
  journal = {Journal of Machine Learning Research},
  year    = {2011},
  volume  = {12},
  number  = {90},
  pages   = {2931--2974},
  url     = {http://jmlr.org/papers/v12/mes11a.html}
}