mgcv. It is called
by gam to obtain the design matrix and penalty matrices for a GAM
set up using penalized regression splines. This is done by calling a mixture of
R routines and compiled C code. For further information on usuage see code for gam.Wood (2000) Modelling and Smoothing Parameter Estimation with Multiple Quadratic Penalties. JRSSB 62(2):413-428
gam mgcv