@article{JMLR:v18:16-657,
  author  = {Christopher Tosh and Sanjoy Dasgupta},
  title   = {Maximum Likelihood Estimation for Mixtures of Spherical Gaussians is NP-hard},
  journal = {Journal of Machine Learning Research},
  year    = {2018},
  volume  = {18},
  number  = {175},
  pages   = {1--11},
  url     = {http://jmlr.org/papers/v18/16-657.html}
}