Tetranucleotide bias and Karlin delta

[MatthewRalston]

Karlin et al, and Riennert et al both reference a tetranucleotide frequency formulation, often referred to as delta, the distance between profiles A and B, and rho-gamma-delta, the di, tri, and tetranucleotide frequency of a sequence abcd, as composed of ab, bc, cd, abc, bcd, aNNd, etc.

This formulation has interest beyond D2 as an alignment-free statistic. Coupled with other anaylses and graphics, a tetranucleotide module could be valuable.