rqss
nonparametric terms
are specified with qss
. Both univariate and bivariate
specifications are possible, and qualitative constraints may also be specified
for the qss terms.qss(x, constraint = "N", lambda = 1, ndum = 0, dummies = NULL, w = rep(1, length(x)))
rqss
for details on how they are assembled. To preserve the
sparsity of the design matrix the first column of each qss term is dropped.
This differs from the usual convention that would have forced qss terms
to have mean zero. This convention has implications for prediction that need to be
recognized. The penalty components for qss terms are based on total
variation penalization of the first derivative (and gradient, for bivariate x)
as described in the references appearing in the help for rqss
.For the bivariate case, package
rqss