A wild guess would be that it's due to univariate and multivariate rings handled by different backends in Sage, one sees this kinds of corner cases errors.
On Mon, Feb 8, 2021 at 10:06 AM John Cremona <[email protected]> wrote: > > 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 <[email protected]> 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 [email protected]. > > 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 [email protected]. > To view this discussion on the web visit > https://groups.google.com/d/msgid/sage-devel/CAD0p0K45OKUuLWegC6sXWHoTWs9ppPf7htmZ1wVyBo_O08%3DNTw%40mail.gmail.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 [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/sage-devel/CAAWYfq20%3DzALr7w3-On2KXfALj5zyzrcmB_Aug%3D5Lyk4g7Cagg%40mail.gmail.com.
