一、对称函数定义:如果函数z=f(x,y)=f(y,x),則称函数z=f(x,y)关于自变量x,y是对称的。如果函数u=f(x,y,z)=f(y,x,z),則称函数u=f(x,y,z)关于x,y是对称的。如果u=f(x,y,z)关于任意两个自变量均是对称的,则 First, the symmetry function definition: If the function z = f (x, y) = f (y, x), then the function z = f (x, y) is said to be symmetric about the independent variable x, y. If the function u=f(x,y,z)=f(y,x,z), the function u=f(x,y,z) is said to be symmetrical about x,y. If u=f(x,y,z) is symmetric about any two independent variables, then