Limit the use of RingExtensions in Drinfeld modules #40421
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Failing test unrelated to this contribution; PR accepted. |
kryzar
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Jul 16, 2025
This was referenced Jul 17, 2025
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sagemathgh-40421: Limit the use of RingExtensions in Drinfeld modules Behaviour before this PR: If `phi` is a Drinfeld module, the method `phi.ore_polring()` used to return an Ore polynomial ring with coefficients in `RingExtension`. This causes a lot of headache because currently an instance of `RingExtension` does not always belong to the appropriate category and, consequently, does not implement all relevant methods and/or is not recognized as what it actually is (e.g. a finite field). In this PR, we propose a simple fix: we let `phi.ore_polring()` return an Ore polynomial ring over the underlying regular field. This only changes the way things are printed, but does not alter the user interface. We will maybe come back later to the original implementation when `RingExtension` will be fixed (which does not seem to be straightforward). ### 📝 Checklist <!-- Put an `x` in all the boxes that apply. --> - [x] The title is concise and informative. - [x] The description explains in detail what this PR is about. - [ ] I have linked a relevant issue or discussion. - [x] I have created tests covering the changes. - [x] I have updated the documentation and checked the documentation preview. URL: sagemath#40421 Reported by: Xavier Caruso Reviewer(s): Antoine Leudière
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sagemathgh-40430: Use the variable name τ instead of t for Drinfeld modules In the theory of Drinfeld module, the classical name of the noncommutative variable is `τ`. However, in Sage, we currently use `t`, which might conflict with other standard notations (often the variable name of the underlying function ring is denoted by `t`). In this PR, we propose to shift to the notation `τ`. It just changes how the outputs are printed (by default), not the interface. ### 📝 Checklist <!-- Put an `x` in all the boxes that apply. --> - [x] The title is concise and informative. - [x] The description explains in detail what this PR is about. - [ ] I have linked a relevant issue or discussion. - [x] I have created tests covering the changes. - [x] I have updated the documentation and checked the documentation preview. ### ⌛ Dependencies sagemath#40420, sagemath#40421 URL: sagemath#40430 Reported by: Xavier Caruso Reviewer(s): Antoine Leudière
vbraun
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sagemathgh-40421: Limit the use of RingExtensions in Drinfeld modules Behaviour before this PR: If `phi` is a Drinfeld module, the method `phi.ore_polring()` used to return an Ore polynomial ring with coefficients in `RingExtension`. This causes a lot of headache because currently an instance of `RingExtension` does not always belong to the appropriate category and, consequently, does not implement all relevant methods and/or is not recognized as what it actually is (e.g. a finite field). In this PR, we propose a simple fix: we let `phi.ore_polring()` return an Ore polynomial ring over the underlying regular field. This only changes the way things are printed, but does not alter the user interface. We will maybe come back later to the original implementation when `RingExtension` will be fixed (which does not seem to be straightforward). ### 📝 Checklist <!-- Put an `x` in all the boxes that apply. --> - [x] The title is concise and informative. - [x] The description explains in detail what this PR is about. - [ ] I have linked a relevant issue or discussion. - [x] I have created tests covering the changes. - [x] I have updated the documentation and checked the documentation preview. URL: sagemath#40421 Reported by: Xavier Caruso Reviewer(s): Antoine Leudière
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Behaviour before this PR:
If
phiis a Drinfeld module, the methodphi.ore_polring()used to return an Ore polynomial ring with coefficients inRingExtension.This causes a lot of headache because currently an instance of
RingExtensiondoes not always belong to the appropriate category and, consequently, does not implement all relevant methods and/or is not recognized as what it actually is (e.g. a finite field).In this PR, we propose a simple fix: we let
phi.ore_polring()return an Ore polynomial ring over the underlying regular field. This only changes the way things are printed, but does not alter the user interface.We will maybe come back later to the original implementation when
RingExtensionwill be fixed (which does not seem to be straightforward).📝 Checklist