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implement natural morphism from cl(f²D) to cl(D) #37074

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yyyyx4
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@yyyyx4 yyyyx4 commented Jan 16, 2024

...for class groups of binary quadratic forms, which we have since #36184.

This map is defined by finding a class representative $[a,b,c]$ for which $f^2 \mid a$ (and $f \mid b$) and then applying the substitution $x \mapsto x/f$. In the code, we do it in prime steps, since that makes finding a suitable representative a little easier.

This can be used, among other things, for determining the kernel of the surjection $\mathrm{cl}(f^2D) \twoheadrightarrow \mathrm{cl}(D)$.

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Documentation preview for this PR (built with commit b75a9a4; changes) is ready! 🎉

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Thanks. LGTM.

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yyyyx4 commented Jan 19, 2024

Thank you!

@vbraun vbraun merged commit e3fd6ec into sagemath:develop Jan 22, 2024
14 of 21 checks passed
@yyyyx4 yyyyx4 deleted the public/bqfclassgroup_quotient_morphisms branch January 22, 2024 01:05
vbraun pushed a commit to vbraun/sage that referenced this pull request Feb 7, 2024
…documentation

    
The possibility to pass discriminants to the constructor instead of
`BQFClassGroup` objects was present for an earlier version of sagemath#37074,
but it was removed during review. However, it seems I forgot to update
the docstring accordingly.
    
URL: sagemath#37233
Reported by: Lorenz Panny
Reviewer(s): Travis Scrimshaw
vbraun pushed a commit to vbraun/sage that referenced this pull request Feb 11, 2024
…documentation

    
The possibility to pass discriminants to the constructor instead of
`BQFClassGroup` objects was present for an earlier version of sagemath#37074,
but it was removed during review. However, it seems I forgot to update
the docstring accordingly.
    
URL: sagemath#37233
Reported by: Lorenz Panny
Reviewer(s): Travis Scrimshaw
@mkoeppe mkoeppe added this to the sage-10.3 milestone Mar 7, 2024
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4 participants