Error when computing torsion group

[HasanSaad2]

Steps To Reproduce

When writing:

t = var('t')
K.<a> = NumberField(20*t^4 + 40*t^3 + 28*t^2 + 8*t + 1) 
EK = EllipticCurve(K,[0,-3/2,0,1/2,0]) 
print(EK.torsion_subgroup())

Expected Behavior

I expect the code to give back the torsion subgroup over the number field.

Actual Behavior

Sagemath throws the following error:
y^2 = x^3 + 12*x^2 defines a singular curve

It appears that the error occurs at this line.

Additional Information

No response

Environment

• Ubuntu 24.04.2 LTS:
• SageMath version 10.3, Release Date: 2024-03-19:

Checklist

• I have searched the existing issues for a bug report that matches the one I want to file, without success.
• I have read the documentation and troubleshoot guide

[DaveWitteMorris]

Thanks for the bug report, and for isolating its location. The problem arises when the monic defining polynomial of the number field has nontrivial denominators in some of its coefficients. As a workaround, you can define the number field with a monic, integral polynomial:

sage: t = var('t')
sage: K.<a> = NumberField(t^4 + 40*t^3 + 560*t^2 + 3200*t + 8000)
sage: EK = EllipticCurve(K,[0,-3/2,0,1/2,0])
sage: print(EK.torsion_subgroup())
Torsion Subgroup isomorphic to Z/2 + Z/2 associated to the Elliptic Curve defined by 
y^2 = x^3 + (-3/2)*x^2 + 1/2*x over Number Field in a with defining polynomial 
t^4 + 40*t^3 + 560*t^2 + 3200*t + 8000

PS I uploaded a pull request to fix this, but if anyone has a smarter approach, they are welcome to close my PR and open a new one.