Carey VJ, Davis AR, Lawrence MF, Gentleman R and Raby BA (2009). “Data structures and algorithms for analysis of genetics of gene expression with Bioconductor: GGtools 3.x.” Bioinformatics, 25(11), pp. 1447–8. http://dx.doi.org/10.1093/bioinformatics/btp169, http://bioinformatics.oxfordjournals.org/content/25/11/1447.long.