@article{JMLR:v21:19-120,
  author  = {Nathan Kallus},
  title   = {Generalized Optimal Matching Methods for Causal Inference},
  journal = {Journal of Machine Learning Research},
  year    = {2020},
  volume  = {21},
  number  = {62},
  pages   = {1--54},
  url     = {http://jmlr.org/papers/v21/19-120.html}
}