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**2.1 Nonlinear measures**

EEG signals, which have a structure similar to random and
irregular patterns, are recently viewed to be fractals.EEG signals, which have
a structure similar to random and irregular patterns, are recently viewed to be
fractals. Fractal is a complex shape and Mandelbrot has argued that there is a
natural dimension in which each fractal sits most parsimoniously. The fractal
Dimension D of a planar curve is D=log (L)/log (d) where L is the length of the
curve and d is the diameter of the planar extent. A running fractal dimension
can give a rough idea about the changing patterns of brain activity during the
entire recording period [6]. Another measure of a complex dynamical system is
that of attractor dimension, which refers to the ability of a space to contain a
set of points (reconstructed phase space vectors). The attractor dimension or
correlation dimension of EEG may be calculated by Singular Value Decomposition
(SVD) of small sets of data on the reconstructed attractor [7].