Additional methods:
Fitting a model that is a sum of Gaussian bases:
- ``ridge`` Ridge regression (L2 loss, [Tikhonov regularization](https://en.wikipedia.org/wiki/Tikhonov_regularization))
- ``lasso`` LASSO regression
(L1 loss, [Least Absolute Shrinkage Selector Operator](https://en.wikipedia.org/wiki/Lasso_(statistics)), [Tibshirani (1996)](https://www.jstor.org/stable/2346178?seq=1#page_scan_tab_contents))
- ``elasticnet`` [Linear regression model](https://en.wikipedia.org/wiki/Elastic_net_regularization) trained with 50% L1 and 50% L2 norm regularization