# Surrogate models¶

When an MDODiscipline is costly to evaluate, it can be replaced by a SurrogateDiscipline cheap to evaluate, e.g. linear model, Kriging, RBF regressor, … This SurrogateDiscipline is built from a few evaluations of this MDODiscipline. This learning phase commonly relies on a regression model calibrated by machine learning techniques. This is the reason why GEMSEO provides a machine learning package which includes the MLRegressionAlgo class implementing the concept of regression model. In addition, this machine learning package has a much broader set of features than regression: clustering, classification, dimension reduction, data scaling, …