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compute matrix of isogeny on n-torsion #34879

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yyyyx4 opened this issue Dec 27, 2022 · 0 comments · Fixed by #35164
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compute matrix of isogeny on n-torsion #34879

yyyyx4 opened this issue Dec 27, 2022 · 0 comments · Fixed by #35164
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c: elliptic curves p: major / 3 t: enhancement

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yyyyx4 commented Dec 27, 2022

The task of computing the matrix by which an isogeny acts on a particular n‑torsion subgroup often comes up in algorithms for supersingular elliptic curves. (In particular, it appears as a subroutine of computing the kernel of an endomorphism-ring ideal.)

This patch adds a simple method to compute such a matrix, based on AdditiveAbelianGroupWrapper.discrete_log().

(The dependency is only necessary for the reference in the "see also" block.)

Depends on #34718

Component: elliptic curves

Author: Lorenz Panny

Branch/Commit: public/matrix_of_isogeny @ 0bc249d

Issue created by migration from https://trac.sagemath.org/ticket/34879
@yyyyx4 yyyyx4 added this to the sage-9.8 milestone Dec 27, 2022
@mkoeppe mkoeppe removed this from the sage-9.8 milestone Jan 29, 2023
@yyyyx4 yyyyx4 mentioned this issue Feb 20, 2023
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vbraun pushed a commit that referenced this issue Mar 26, 2023
gh-35164: compute the matrix of an isogeny on a given n-torsion subgroup
dc4930a 
    
Fixes #34879.
    
URL: #35164
Reported by: Lorenz Panny
Reviewer(s): John Cremona, Lorenz Panny
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compute the matrix of an isogeny on a given n-torsion subgroup yyyyx4/sage
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@jhpalmieri @mkoeppe @yyyyx4