For practical applications, data pre-processing is often a
necessary step in the development of solution. In the simplest
case, pre-processing may take the form of a linear
rescaling of the input variables so that they have similar
values regardless of the units in which each of these is
expressed. More complex pre-processing may involve
reduction of the dimensionality of the input data. The fact
that such dimensionality reduction can lead to improved
performance may appear somewhat paradoxical, since it
cannot increase the information content of the input data,