2021-01-28 15:53:44 +0100 received badge ● Notable Question (source) 2020-01-01 19:57:51 +0100 received badge ● Popular Question (source) 2015-09-28 19:54:58 +0100 received badge ● Scholar (source) 2015-09-28 15:41:27 +0100 commented answer Compute $j$-invariant of elliptic curve in non-Weierstrass form with arbitrary coefficients Looks good, thanks a lot! 2015-09-28 14:35:53 +0100 received badge ● Student (source) 2015-09-28 12:53:15 +0100 asked a question Compute $j$-invariant of elliptic curve in non-Weierstrass form with arbitrary coefficients One can compute the $j$-invariant of an elliptic curve not in Weierstrass form in Sage via the following (where the curve $x+x^2+y-x^2y-xy^2+x^2y^2=0$ -- not in Weierstrass form -- is used as an example): x,y = polygen(QQ,'x,y') E = Jacobian(x+x^2+y-x^2*y-x*y^2+x^2*y^2) E.j_invariant() If we include numerical coefficients of the various terms, this still works. However, I would like Sage to compute the j-invariant of such curves in non-Weierstrass form with arbitrary coefficients, e.g. $ax+bx^2+cy-dx^2y-exy^2+fx^2y^2$. Is this possible? I tried including the line: var('a,b,c,d,e,f') But got an error. Can anyone help? Thanks!