Opened 5 years ago
Closed 5 years ago
#21195 closed defect (fixed)
cardinality_exhaustive incorrect for general curves of genus 1
Reported by: | pbruin | Owned by: | |
---|---|---|---|
Priority: | major | Milestone: | sage-7.4 |
Component: | algebraic geometry | Keywords: | hyperelliptic curve finite field |
Cc: | jpflori | Merged in: | |
Authors: | Peter Bruin | Reviewers: | Jean-Pierre Flori |
Report Upstream: | N/A | Work issues: | |
Branch: | af72dd9 (Commits, GitHub, GitLab) | Commit: | af72dd96a6381aa23f2f7119389e47c920ee4c9a |
Dependencies: | #19122 | Stopgaps: |
Description
After #19122, counting points at infinity still needs to be fixed for hyperelliptic curves of genus 1 given by an equation y^2 + h(x)*y = f(x)
when h != 0
. Consider the following example (cf. comment:17:ticket:19122):
def test(p): S.<z> = GF(p)[] D = HyperellipticCurve(-z^2 + z, z^2) return D.count_points_exhaustive()
Running this for p = 2
and p = 3
gives
sage: test(2) [4] sage: test(3) [4] # or [3], after #19122
Both answers should be 5.
Change History (3)
comment:1 Changed 5 years ago by
- Branch set to u/pbruin/21195-cardinality_exhaustive
- Cc jpflori added
- Commit set to af72dd96a6381aa23f2f7119389e47c920ee4c9a
- Status changed from new to needs_review
comment:2 Changed 5 years ago by
- Reviewers set to Jean-Pierre Flori
- Status changed from needs_review to positive_review
Looks good to me! Thanks Peter.
comment:3 Changed 5 years ago by
- Branch changed from u/pbruin/21195-cardinality_exhaustive to af72dd96a6381aa23f2f7119389e47c920ee4c9a
- Resolution set to fixed
- Status changed from positive_review to closed
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The attached branch fixes the bug basically by removing the special case g = 1 in
cardinality_exhaustive()
. It also streamlines the code, making the parallels between the computations in the various cases (affine and infinite points, even and odd characteristic) more apparent.