Re: [sage-devel] possible bug: kernel of ring homomorphism
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. = QQ[] > B. = 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 >> 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 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. = QQ[] >> > > B. = 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.
Re: [sage-devel] possible bug: kernel of ring homomorphism
For reference this is also asked on Ask Sage: https://ask.sagemath.org/question/55618 -- 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/d43f0d17-d243-40ec-98be-65e8ea5f970bn%40googlegroups.com.
Re: [sage-devel] possible bug: kernel of ring homomorphism
It seems that unfortunately the problem persists for multivariate rings as well: A. = QQ[] B. = 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 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 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. = QQ[] > > > B. = 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/d4bb76c9-3002-47b2-9275-3977ce1912a8n%40googlegroups.com.
Re: [sage-devel] possible bug: kernel of ring homomorphism
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 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 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. = QQ[] > > B. = 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. -- 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/CAAWYfq20%3DzALr7w3-On2KXfALj5zyzrcmB_Aug%3D5Lyk4g7Cagg%40mail.gmail.com.
Re: [sage-devel] possible bug: kernel of ring homomorphism
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 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. = QQ[] > B. = 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.
[sage-devel] possible bug: kernel of ring homomorphism
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. = QQ[] B. = 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.
