Principal component analysis (PCA) can be successfully applied to a variety
of signal processing problems. Different analyzers have been reported in t
he scientific literature; among others, the Adaptive Principal component EX
tractor (APEX) by Kung and Diamantaras has attracted much interest in the s
cientific community since it involves a specific neural architecture and a
specific learning theory. The aim of this brief is to present a general cla
ss of APEX-like learning rules (referred to as psi -APEX) and to illustrate
their features by theoretical and numerical analysis.