Non-linear transformations of the data

Another approach is to transform the original columns of a measurement table by suitable non-linear functions in order to obtain some desirable effect. This is 

The logarithmic transformation prior to column- or double-centered PCA (Section 31.3) can be considered as a special case of non-linear PCA. The procedure tends to make the row- and column-variances more homogeneous, and allows us to interpret the resulting biplots in terms of log ratios. 

---