A related approach is offered by the non-linear PCA
criteria [82,83,84,112]. These
objective functions are based on the
idea of introducing a non-linearity in well-known objective
functions used in PCA.
Take, for example, the recursive definition of PCA in Eq. (3).
Introducing a non-linearity g(.) in the formula, one obtains
Sometimes in connection with the non-linear PCA criteria, a 'bottom-up' approach is used, as with non-linear cross-correlations. Explicit contrast functions may not be formulated, and the algorithms are often obtained directly from existing PCA algorithms by introducing a suitable non-linearity [112,84].