@article{chalupka2013,
  title={A framework for evaluating approximation methods for {G}aussian process regression},
  author={Krzysztof Chalupka and Christopher K. I. Williams and Iain Murray},
  journal={Journal of Machine Learning Research},
  volume={14},
  pages={333-−350},
  year={2013},
  url={http://jmlr.csail.mit.edu/papers/v14/chalupka13a.html}
}