A special smooth.construct method function for creating tensor product smooths from any
combination of single penalty marginal smooths, using the construction of Wood, Scheipl and Faraway (2013).
# S3 method for t2.smooth.spec
smooth.construct(object, data, knots)a smooth specification object of class t2.smooth.spec,
usually generated by a term like t2(x,z) in a gam model formula
a list containing just the data (including any by variable) required by this term,
with names corresponding to object$term (and object$by). The by variable
is the last element.
a list containing any knots supplied for basis setup --- in same order and with same names as data.
Can be NULL. See details for further information.
An object of class "t2.smooth".
Tensor product smooths are smooths of several variables which allow the degree of smoothing to be different with respect
to different variables. They are useful as smooth interaction terms, as they are invariant to linear rescaling of the covariates,
which means, for example, that they are insensitive to the measurement units of the different covariates. They are also useful
whenever isotropic smoothing is inappropriate. See t2, te, smooth.construct and
smooth.terms. The construction employed here produces tensor smooths for which the smoothing penalties are non-overlapping portions of the identity matrix. This makes their estimation by mixed modelling software rather easy.
Wood, S.N., F. Scheipl and J.J. Faraway (2013) Straightforward intermediate rank tensor product smoothing in mixed models. Statistics and Computing 23: 341-360.