Evaluating discriminant of a polynomial in Z_n[x]/<x^r-1>
Consider the following code
Zn=Zmod(n)
R = PolynomialRing(Zn,'x')
F = R.quotient((x**r)-1)
y=F((x+1))
f=F(y**n)
Clearly f will be a polynomial in xbar , I want to consider this polynomial as a polynomial in $ \mathbb{Z}[x] $ and evaluate its discriminant.
I tried "f.polynomial()" but it is not working. Any suggestions ?