Table 3.

Feature extraction from electronic nose signals.

Indices	Name	Formula
VAR	Variance value	$VAR=\frac{1}{N}{\displaystyle \sum _{i=1}^N{\left(c_i-\overline{c}\right)}^2}$
INV	Integral value	$INV=c(i)\Delta t$
RSAV	Relative steady-state average value	$RSAV=\frac{1}{N-t_0}{\displaystyle \sum _{t_o}^T{c}_{{}^i}}$
ADV	Average differential value	$ADV=\frac{1}{N-1}{\displaystyle \sum _{i=1}^{N-1}\frac{c_{i+1}-c_i}{\Delta t}}$
KURT	Kurtosis coefficient	$KURT=\frac{\frac{1}{N}{\displaystyle \sum _{i=1}^N{(c_i-\overline{c})}^4}}{(\frac{1}{N}{\displaystyle \sum _{i=1}^N{({(c_i-\overline{c})}^2)}^2}}-3=\frac{m_{{}^4}}{m_2^2}-3$
SKEW	Coefficient of skewness	$SKEW=\frac{\sqrt{\mathrm{N}(\mathrm{N}-1)}}{N-2}\frac{\frac{1}{N}{\displaystyle \sum _{i=1}^N{({\mathrm{c}}_i-\overline{c})}^3}}{(\frac{1}{N}{\displaystyle \sum _{i=1}^N{({({\mathrm{c}}_i-\overline{c})}^2)}^{\frac{3}{2}}}}$