This function normalizes the 2WR matrix (or any 2D matrix) according to the species (rows) or to the genes (columns), by dividing each row or each column by its median.

## Arguments

- mat
A matrix

- what
Character string indicating whether the matrix should be normalized and how. If what="none", the matrix is not normalized (the default), if what="species", the matrix is normalized so that the difference between species is increased, and if what="genes", the matrix is normalized so that the difference between genes is increased. Normalization consists in dividing either each row or each columns by its median.