I am trying to run this code
t = var('t')
K. = NumberField(20t^4 + 40t^3 + 28t^2 + 8t + 1)
EK = EllipticCurve(K,[0,3/2,0,1/2,0])
print(EK.torsion_subgroup())
However, Sage is throwing the following error:
y^2 = x^3 + 25*x^2 defines a singular curve
I am not exactly sure what the problem is since the original curve is a nonsingular curve. On the other hand, it appears that when I use K to be the full 5-division field, for example, there is no error. However, that field is much larger than what I want to consider.
Any ideas what's going wrong?
Thanks.