Table 1.

Summary of several commonly-used mean functions [26].

Mean Function	Equation Expression
Zero	0
Constant	$\complement$; ${\left(x\times x^{\prime }+{\mathsf{\sigma }}_0^2\right)}^p$
Linear	$\mathsf{\alpha }\text{x}+\mathrm{b}$
Poly	${{\displaystyle \sum }}_{\mathit{i}}^{\mathit{N}}{\alpha }^{\mathit{i}}{\mathit{x}}^{\mathit{N}-\mathit{i}}$