left identity element

For positive real numbers x and y with x≠y, and for parameter r∈R, let Mr(x, y), L(x,y) and I(x,y) denote the power, logarithmic and identric means of x and y, respectively.

设Ｍｒ（ｘ，ｙ）、Ｌ（ｘ，ｙ），和Ｉ（ｘ，ｙ）依次为ｘ、ｙ的幂平均、对数平均和幺元平均（具体由２－４式定义）。