discriminant of multivariate polynomial
If I do
R.<x,z,I>=QQ[]
f_str = 'x**3 + x*z +1'
f = eval(f_str)
f.discriminant(x)
this works out correctly, giving
-4*z^3 - 27
But if I instead replace the coefficient of any monomial with a rational, such as
R.<x,z,I>=QQ[]
f_str = '1.0*x**3 + x*z +1'
f = eval(f_str)
f.discriminant(x)
I get the following error:
AttributeError: 'MPolynomial_polydict' object has no attribute 'discriminant'
Can someone explain how to make it work?