Définitions
1.NounA function of the form
f
(
x
1
,
x
2
,
…
,
x
n
)
=
∑
k
=
1
K
c
k
x
1
a
1
k
⋯
x
n
a
n
k
{\displaystyle f(x_{1},x_{2},\dots ,x_{n})=\sum _{k=1}^{K}c_{k}x_{1}^{a_{1k}}\cdots x_{n}^{a_{nk}}}
, where all the coordinates
x
i
{\displaystyle x_{i}}
and coefficients
c
k
{\displaystyle c_{k}}
are positive real numbers, and the exponents
a
i
k
{\displaystyle a_{ik}}
are real numbers.