Ask Your Question

Challenges with subgroup elements

asked 2022-02-05 01:11:27 +0200

AlonAmit gravatar image

updated 2022-02-05 01:49:28 +0200

I'm running into apparent inconsistencies when studying subgroups of the unit group of a cyclotomic field.

k = CyclotomicField(7,'z')
U = k.unit_group()
z = k.gen()
a = 1+z
b = a^(-1)
T = U.subgroup([U(a)])
print(U(a) in U)
print(U(b) in U)
print(U(a) in T)
print(U(b) in T)

What I'm getting is:


which doesn't make sense. $T$ is a subgroup, so if it contains $a$ it must also contain $a^{-1}$. The group $U$ gets it right, but the subgroup $T$ does not. I'm guessing this is some coercion issue, but I'm not sure why it's happening, if it's a bug, and how to work around it.

(Checked this on the Sage Cell Server and CoCalc with Sage 9.4)

edit retag flag offensive close merge delete


Please try SageMath 9.5, as there was a fix in this area recently.

rburing gravatar imagerburing ( 2022-02-05 11:42:27 +0200 )edit

Implentation of subgroups of unit groups is known to be buggy. E.g., see along the same lines.

Max Alekseyev gravatar imageMax Alekseyev ( 2022-02-05 13:43:01 +0200 )edit

Wow. Thank you both. Yeah, ver 9.5 resolves this issue. Whew!

AlonAmit gravatar imageAlonAmit ( 2022-02-07 03:06:40 +0200 )edit

1 Answer

Sort by ยป oldest newest most voted

answered 2022-02-07 10:25:24 +0200

rburing gravatar image

The issue is fixed in SageMath 9.5.

edit flag offensive delete link more

Your Answer

Please start posting anonymously - your entry will be published after you log in or create a new account.

Add Answer

Question Tools

1 follower


Asked: 2022-02-05 01:11:27 +0200

Seen: 368 times

Last updated: Feb 07 '22