This function contributes to solving a nonnegative least square linear
problem using normal equations and the fast combinatorial strategy from Van
Benthem et al. (2004). This implementation is similar to that included in the
NMF R package by Renaud Gaujoux and Cathal Seoighe,
and it is tailored to the data used in the mutational signature analysis.
For more info, see: https://CRAN.R-project.org/package=NMF