* parameter for [Huber loss](https://en.wikipedia.org/wiki/Huber_loss"Huber loss - Wikipedia"). Will be used in regression task.
*```fair_c```, default=```1.0```, type=double
* parameter for [Fair loss](http://research.microsoft.com/en-us/um/people/zhang/INRIA/Publis/Tutorial-Estim/node24.html). Will be used in regression task.
* parameter for [Fair loss](https://www.kaggle.com/c/allstate-claims-severity/discussion/24520). Will be used in regression task.