It looks like a bug to me. f.kernel() expands to f._inverse_image_ideal(f.codomain().zero_ideal()) and f.codomain().zero_ideal() looks OK so the problem must be in the inverse image. The author is apparently Simon King (2011). Simon, can you help?
John On Mon, 8 Feb 2021 at 09:20, Akos M <matszangosz.a...@gmail.com> wrote: > > Hi, > > I'm not sure whether this is a bug or not, but the kernel of a ring > homomorphism to a quotient ring gives unexpected results: > > A.<t> = QQ[] > B.<x,y> = QQ[] > H = B.quotient(B.ideal([B.1])) > f = A.hom([H.0], H) > f > f.kernel() > > outputs: > > Ring morphism: From: Univariate Polynomial Ring in t over Rational Field > To: Quotient of Multivariate Polynomial Ring in x, y over Rational Field by > the ideal (y) Defn: t |--> xbar > Principal ideal (t) of Univariate Polynomial Ring in t over Rational Field > > whereas the kernel of f:A[t]->B[x,y]->B[x,y]/(y), for f(t)=x should be (0). > > Is this a bug? > > Thanks, > Akos > > -- > You received this message because you are subscribed to the Google Groups > "sage-devel" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to sage-devel+unsubscr...@googlegroups.com. > To view this discussion on the web visit > https://groups.google.com/d/msgid/sage-devel/3eeea5f7-4ea2-4586-bbb6-04d00c0d4fa9n%40googlegroups.com. -- You received this message because you are subscribed to the Google Groups "sage-devel" group. To unsubscribe from this group and stop receiving emails from it, send an email to sage-devel+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/sage-devel/CAD0p0K45OKUuLWegC6sXWHoTWs9ppPf7htmZ1wVyBo_O08%3DNTw%40mail.gmail.com.
