Nomenclature	Explanation
$e$	$\mathrm{Lower}\mathrm{case}\mathrm{letter}\mathrm{variable}\mathrm{is}\mathrm{a}\mathrm{scalar}$
$\mathit{e}$	Bold lower case letter variable is a vector
$\mathit{E}$	Bold upper case letter variable is a matrix
$\begin{array}{c}\mathit{e}=\left\{e_1,e_2\right\}\\ ={\left(e_1,e_2\right)}^T\end{array}$	$\mathrm{Equivalent}\mathrm{vector}\mathrm{notations}$
$\mathit{E}=\left[\begin{array}{cc}{e}_{11}& e_{12}\\ e_{21}& e_{22}\end{array}\right]$	Matrix notation
$\mathsf{ϵ}$	Denotes the machine precision according to IEEE 754-2008