The trace of the hat matrix corresponds to the effective degrees of freedom (edf) of a generalized additive model. The edf is used as an internal measure of model complexity.
calcTrA(W, X, lambda=0)
Weight matrix of the pseudo iterated least squares algorithm. See function calcWdiag
Design matrix of the covariates.
Regularization parameter of kernel ridge regression.
Effective degrees of freedom of a generalized additive model with regularization (numeric scalar).
Simon N. Wood, (2006), Generalized Additive Models: An Introduction with R, Taylor \& Francis Group LLC