Added the Subring package

[fragandi]

Hi everyone, here is a small package with methods for handling subrings based on the ones available in SAGBI and in InvariantRing

[d-torrance]

Thanks for the contribution!

In addition to the other comments, there's also a typo:

M2/Macaulay2/packages/Subring/SubringDoc.m2:282: accessable ==> accessible

[d-torrance]

Also, "Subring" should be added to the =distributed-packages file.

[fragandi]

Also, "Subring" should be added to the =distributed-packages file.

I could not find this file, can you give me more details on the path?

[d-torrance]

It's at M2/Macaulay2/packages/=distributed-packages

[fragandi]

Also, "Subring" should be added to the =distributed-packages file.

I could not find this file, can you give me more details on the path?

NWM I thought a file could not start with = but I guess that's ok!

[mahrud]

@fragandi is the plan to eventually make SubalgebraBases depend on this package? Because currently the subring conflict makes them not usable at the same time.

[fragandi]

I have talked to Ollie @ollieclarke8787 before this PR and the idea is indeed to have Subrings as part of the M2 packages and then have SubalgebrasBases call on it. Maybe Ollie you can look into this conflict? Or let me know if I messed up something in the PR.

[mahrud]

The current failure was because you forgot AuxiliaryFiles => true in the package header. The packages are fine alone, just not usable at the same time right now.

[d-torrance]

@fragandi - Just a friendly reminder about this PR

[fragandi]

@ollieclarke8787 and I will follow up on this around the time of the Warwick workshop (6/29/26). Converted to draft until then.

[fragandi]

@galettof and @trevorkarn might also be interested in this PR. We have a check-in meeting scheduled for June 22, let me know if you would like a link!

[ollieclarke8787]

Some updates on the above changes:

• The type Subring in the Subrings package is now completely interchangeable with the type Subring in SubalgebraBases so it should be a matter of importing the Subrings in SubalgebraBases and removing parts of that package.
• I currently get an error when installing the package, which suggests there may be a problem with the documentation (since needsPackage "Subrings" seems to be fine) - but I'm having trouble tracking this down.

[mahrud]

Why not just install a method flattenRing Subring?

[ollieclarke8787]

flattenedRing was defined in SubalgebraBases so I pulled it across to Subrings, it should be possible to swap over to using flattenRing but the underlying meaning seems a little different: the flattenedRing S of S:Subring is equivalent to flattenRing ambient S. For now I've added flattenRing in b4777fe

[ollieclarke8787]

isSubringElement now uses hooks, so it should be possible modify SubalgebraBases to build on top of it. TODO: add a new hook to a function that checks if a sagbi basis (of high enough degree) is already computed and return whether the element subducts to zero against the sagbi basis.

[ollieclarke8787]

SubalgebraBases seems to be functioning with the Subrings package but the docs have a lot of ambiguous reference warnings.

[fragandi]

Spoke with Ollie @ollieclarke8787 today, his work addressed the comments above, let us know if there any other further suggested edits.