A sparse counterpart of Reichel and Gragg's package QRUP (Q1044853)

The authors deal with the problem of maintaining the triangular factor of a sparse QR factorization when columns are added and deleted and \(Q\) cannot be stored for sparsity reasons. In this respect they adapt the sparse direct methodology of \textit{Å. Björck} [Numer. Math. 54, No.~1, 19--32 (1988; Zbl 0659.65039)] and \textit{U. Oreborn} [A direct method for sparse nonnegative least squares problems, Lic. Thesis, Dept. Math., Linköping Univ. (1986)], without formatting \(A^T A\). The \texttt{Matlab} implementations presented in the paper use a suitable row and column numbering within a static triangular sparsity computed in advance.