Drinfeld Modules: Default to zero endomorphism in .hom and avoid inversion of zero endomorphism
#38964
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Documentation preview for this PR (built with commit b192330; changes) is ready! 🎉 |
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Looks good to me. Thanks. |
xcaruso
approved these changes
Nov 14, 2024
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This PR fixes #38953 and is inspired by the error raised in the issue:
__invert__, so thatphi.hom(a)actually returns an invertible morphism.phi.hom(K.zero())does not return any homomorphism: Since the codomain is not specified, it tries to find a codomain via the.velu-method, but this only works if the given element defines an isogeny, whichK.zero()does not. Instead of raising an error for this special case in.hom, it seems more robust to default to the zero endomorphism ofselfinstead.isogin the.velu-method.