While IPCA returns the estimated eigenvectors as a
matrix that represents subspaces of data and the corresponding
eigenvalues as a row vector, FastICA searches for the independent
directions w where the projections of the input
data vectors will maximize the non-Gaussianity. It is based
on minimizing the approximate negentropy function [19]
given by J(x) = i ki{E(Gi(x)) − E(Gi(v))}2 using Newton’s
method. Where G(x) is a nonquadratic function of the random
variable x and E is its expected value.