list of 5 elements: df vector, cv vector of corresponding
cross-validation scores, se vector of standard error estimates,
df_min cross-validation minimiser, df_1se largest smoothing
parameter within CV score within one standard error of df_min.
Arguments
x
vector of datapoints
df
vector of smoothing parameters for the
non-parametric score estimator, corresponding to the
effective degrees of freedom for a smoothing spline.
nfolds
integer number of cross-validation folds.
tol
numeric tolerance, minimum distance between neighbouring points,
to avoid singularities.
nmax
if specified, overrides tol as maximal number of unique points.