.. _DefCorrelationLength: Definition of Term: Correlation length ====================================== The degree of :ref:`smoothness` of an :ref:`emulator` is determined by its correlation function. Smoothness is in practice controlled by :ref:`hyperparameters` in the correlation function that define how slowly the correlation between the simulator outputs at two input points declines as the distance between the points increases. These hyperparameters are typically called correlation length parameters. Their precise role in determining smoothness depends on the form of correlation function.