To get back to the question, did you find the inverse by hand or is there something in Sage to help out? I have potentially a large number of cubics I'd like to carry this out with and if there's a way to avoid doing it by hand each time that'd be great.
On Saturday, May 24, 2014 4:38:48 PM UTC-4, Nils Bruin wrote: > > On Saturday, May 24, 2014 9:18:29 AM UTC-7, Volker Braun wrote: >> >> Its a 4:1 map so you can't invert it... >> > > I would find that surprising. For a general plane cubic, there are good > recipes for getting a 9:1 map to a Weierstrass model in general and a 1:1 > map when a rational point is specified. A 4:1 map is rather unnatural to > get in that situation. You'd expect that from a y^2=quartic in x model. > > Indeed, the map returned is invertible, the inverse being: > > [ -12*x*z - 4*y*z, 32*x*z, x^2 - 28*x*z - 4*y*z] > > > -- You received this message because you are subscribed to the Google Groups "sage-support" group. To unsubscribe from this group and stop receiving emails from it, send an email to sage-support+unsubscr...@googlegroups.com. To post to this group, send email to sage-support@googlegroups.com. Visit this group at http://groups.google.com/group/sage-support. For more options, visit https://groups.google.com/d/optout.
