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Possible bug in Betti diagram https://www.singular.uni-kl.de/forum/viewtopic.php?f=10&t=2671 |
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Author: | AG [ Fri Sep 22, 2017 3:26 pm ] |
Post subject: | Possible bug in Betti diagram |
We know that if $I$ is a graded ideal in a polynomial ring, then the graded Betti numbers of $I$ are at most the corresponding graded Betti numbers of the initial ideal of $I$ with respect to any monomial order (See Corollary 3.3.3 of the book by Herzog and Hibi). The following code in Singular says differently. Where is my mistake? Code: > ring r = 0, (x, y,z, u,v, w, a, b, c, d), Dp; > ideal P = zw+u2+uv, ya+zu+uv, xb+y2+yz+zu, uvcd+wac+wb2, zvcd-uac-ub2-vac-vb2; > P; P[1]=zw+u2+uv P[2]=ya+zu+uv P[3]=xb+y2+yz+zu P[4]=uvcd+wac+wb2 P[5]=zvcd-uac-ub2-vac-vb2 > P = std(P); > ideal P' = lead(P); > P'; P'[1]=zw P'[2]=ya P'[3]=xb P'[4]=uvcd P'[5]=zvcd > resolution R = mres(P, 0); > resolution R' = mres(P', 0); > print(betti(R), "betti"); 0 1 2 3 4 ------------------------------------ 0: 1 - - - - 1: - 3 - - - 2: - - 4 - - 3: - 2 1 3 - 4: - - 4 2 1 5: - - - 2 1 ------------------------------------ total: 1 5 9 7 2 > print(betti(R'), "betti"); 0 1 2 3 4 ------------------------------------ 0: 1 - - - - 1: - 3 - - - 2: - - 3 - - 3: - 2 2 1 - 4: - - 4 4 - 5: - - - 2 2 ------------------------------------ total: 1 5 9 7 2 |
Author: | hannes [ Sat Sep 23, 2017 1:09 pm ] |
Post subject: | Re: Possible bug in Betti diagram |
Your ideal is nor homogeneous, see https://www.singular.uni-kl.de:8002/trac/ticket/810#comment:1 |
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