Opened 15 months ago
Closed 13 months ago
#32269 closed defect (fixed)
Isogenies prime degree fails on some CM curves
Reported by:  Sachi Hashimoto  Owned by:  

Priority:  major  Milestone:  sage9.5 
Component:  elliptic curves  Keywords:  elliptic curves, isogeny, CM 
Cc:  Alex J. Best  Merged in:  
Authors:  Alex J. Best  Reviewers:  Edgar Costa 
Report Upstream:  N/A  Work issues:  
Branch:  6b6dc19 (Commits, GitHub, GitLab)  Commit:  6b6dc19fed27e3d0b5a4b529e1937986640aa14b 
Dependencies:  Stopgaps: 
Description
The code:
K.<a> = QuadraticField(11) E = EllipticCurve(K, [0,1,0,117,541]) E.isogenies_prime_degree(53)
returns an empty list. But, since E has CM by the ring of integers of K, it has to have an isogeny of degree p for p splitting in K, so this doesn't make sense.
If you import isogenies_prime_degree_general from isogeny_small_degree.py then
isogenies_prime_degree_general(E,53)
correctly returns
[Isogeny of degree 53 from Elliptic Curve defined by y^2 = x^3 + x^2 + (117)*x + (541) over Number Field in a with defining polynomial x^2 + 11 with a = 3.316624790355400?*I to Elliptic Curve defined by y^2 = x^3 + x^2 + (98560*a+42123)*x + (12561472*a61946205) over Number Field in a with defining polynomial x^2 + 11 with a = 3.316624790355400?*I, Isogeny of degree 53 from Elliptic Curve defined by y^2 = x^3 + x^2 + (117)*x + (541) over Number Field in a with defining polynomial x^2 + 11 with a = 3.316624790355400?*I to Elliptic Curve defined by y^2 = x^3 + x^2 + (98560*a+42123)*x + (12561472*a61946205) over Number Field in a with defining polynomial x^2 + 11 with a = 3.316624790355400?*I]
Change History (13)
comment:1 Changed 15 months ago by
Branch:  → u/alexjbest/isognf 

Commit:  → 96561b332f35d1e9d56b190ce4a09221b779fb29 
Status:  new → needs_info 
Work issues:  → wait for CI 
comment:2 Changed 15 months ago by
Status:  needs_info → needs_review 

comment:3 Changed 15 months ago by
Commit:  96561b332f35d1e9d56b190ce4a09221b779fb29 → 251c8297a5872756256a42e7a506c95ed5a91ed8 

Branch pushed to git repo; I updated commit sha1. New commits:
251c829  output

comment:4 Changed 15 months ago by
Authors:  → Alex J. Best 

comment:5 Changed 15 months ago by
LGTM, but that test with ell = 53
is not going to fly.
Why not ell = 37
? it is equally broken and takes 1/6 of the time.
comment:6 Changed 14 months ago by
@edgarcosta, right the example in code uses l=37, it might still need marking as # long time though, I'm not sure.
comment:7 Changed 14 months ago by
Upsidaisy! Ignore my comment then.
I was hoping that the patch bot would tell us what to do regarding the necessity of the marking as # long
comment:8 Changed 14 months ago by
Commit:  251c8297a5872756256a42e7a506c95ed5a91ed8 → 6b6dc19fed27e3d0b5a4b529e1937986640aa14b 

Branch pushed to git repo; I updated commit sha1. New commits:
6b6dc19  fix doctest

comment:9 Changed 14 months ago by
Work issues:  wait for CI 

comment:10 Changed 14 months ago by
Status:  needs_review → positive_review 

comment:11 Changed 14 months ago by
Reviewers:  → Edgar Costa 

comment:12 Changed 14 months ago by
Milestone:  sage9.4 → sage9.5 

comment:13 Changed 13 months ago by
Branch:  u/alexjbest/isognf → 6b6dc19fed27e3d0b5a4b529e1937986640aa14b 

Resolution:  → fixed 
Status:  positive_review → closed 
New commits:
attempt to fix 32269