Posynomial

A posynomial, also known as a posinomial in some literature, is a function of the form 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 and coefficients c_k are positive real numbers, and the exponents a_{ik} are real numbers. Posynomials are closed under addition, multiplication, and nonnegative scaling.