If you use GPfit, please cite it with the following bibtex:
@article{hoburg2016data,
title={Data fitting with geometric-programming-compatible softmax functions},
author={Hoburg, Warren and Kirschen, Philippe and Abbeel, Pieter},
journal={Optimization and Engineering},
volume={17},
number={4},
pages={897--918},
year={2016},
publisher={Springer}
}