Functions in polynomials rings
I want to define a function in a polynomial ring in several variables.
R.<x1,x3,x5>=PolynomialRing(QQ)
I am trying to define a function that takes $(i,j)$ to $x_i^j$.
I tried
def f(i,j):
return xi^j
This does not work. I tried replacing xi with x[i], that doesn't work. Can someone please tell me what I am doing wrong and how to fix it? If instead of taking 3 variables I take only 1 variable then the method works.