Elements of q or p that are missing will cause the
corresponding elements of the result to be missing.
References
Charles Kooperberg, Charles J. Stone and Young K. Truong (1995).
Hazard regression. Journal of the American Statistical
Association, 90, 78-94.
Charles J. Stone, Mark Hansen, Charles Kooperberg, and Young K. Truong.
The use of polynomial splines and their tensor products in extended
linear modeling (with discussion) (1997). Annals of Statistics,
25, 1371--1470.