This is a design matrix arising from a bivariate smoothing problem using penalized triogram fitting. It is used in the SparseM vignette to illustrate the use of the sparse matrix image function.
data(triogramX)A 375 by 100 matrix stored in compressed sparse row format
Koenker, R and Ng, P. (2002). SparseM: A Sparse Matrix Package for R, http://www.econ.uiuc.edu/~roger/research