I need some classical invariant theory and didn't find the formulae in
Sage, so I'm adding it. My plan is to have a single invariant_theory
factory object in the global namespace:
sage: R.<x,y,z> = QQ[]
sage: cubic = invariant_theory.ternary_cubic(x^3+y^3+z^3)
sage: cubic.T_invariant()
1
sage: R.<x,y,t> = GF(7)[]
sage: quartic = invariant_theory.binary_quartic(x^4+y^4+t*x^2*y^2,
[x,y])
sage: quartic.EisensteinD()
3*t^2 + 1
sage: quartic.h_covariant()
2*x^5*y*t^2 - 2*x*y^5*t^2 - x^5*y + x*y^5
I'm unsure of where to put the code; Tentatively I've stuffed it into
sage/schemes/invariant_theory.py but I'm open for suggestions. Thoughts?
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