# 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, …