Thank you for reporting this problem. I have opened https://trac.sagemath.org/ticket/31367 for it and will provide a fix there shortly.
Akos M schrieb am Montag, 8. Februar 2021 um 11:42:59 UTC+1: > It seems that unfortunately the problem persists for multivariate rings as > well: > > A.<t,u> = QQ[] > B.<x,y,z> = QQ[] > H = B.quotient(B.ideal([B.2])) > f = A.hom([H.0, H.1], H) > f > f.kernel() > > Ring morphism: > From: Multivariate Polynomial Ring in t, u over Rational Field > To: Quotient of Multivariate Polynomial Ring in x, y, z over Rational > Field by the ideal (z) > Defn: t |--> xbar > u |--> ybar > Ideal (-t, -u, 0) of Multivariate Polynomial Ring in t, u over Rational > Field > > I have the impression that the fact that the ring homomorphism is to a > quotient ring introduces the error, but that's just a wild guess. > On Monday, February 8, 2021 at 11:09:52 AM UTC+1 dim...@gmail.com wrote: > >> 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 <john.c...@gmail.com> >> 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 <matszang...@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+...@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+...@googlegroups.com. >> > 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 sage-devel+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/sage-devel/806d3b24-3f01-49b5-89e1-50e218b427d0n%40googlegroups.com.
