Tagging - 2019-04-20

3:44 AM

@XanderHenderson Since there're no tags about "semisimple-***" in MO, I was a little skeptical if that tag is necessary enough at that time.

@ArnaudD. You can edit this since it's resolved.

3

A: Tag management 2019

Proposal: synonymize lft with mobius-transformation. They're the same thing in most cases.

Info of mobius-transformation says "Möbius transformations, sometimes called linear fractional transformations"

Martin Sleziak

4:21 AM

@Andrews I'd say that to consider it resolved, we should probably crate also accessible-categories tag. But its's good that you reminded Arnaud D. of the issue.

There are two questions which had this tag when it was created earlier: $\lambda$-pure morphisms in $\lambda$-accessible categories are monos, unclear proof and $\lambda$-accessible categories, unclear proof

SEDE queries: data.stackexchange.com/math/query/927958/… data.stackexchange.com/math/query/883845/…

Some past questions where this tag might be suitable: Subcategory of accessible category, Is the category of Banach spaces and bounded linear maps accessible?, Question about accessibility of category of free abelian groups. ...

Martin Sleziak

4:40 AM

2

A: Should we divide [tag:dimension-theory] into 2 tags, one for topology, and one for algebra?

My own area of research is fractal geometry. In fractal geometry, there are various notions of dimension (Hausdorff, box, Minkowski, Assouad, packing, complex etc.). Very roughly speaking, the dimension of a set in a metric space describes how the "volume" of a set scales when the set is scaled...

Since replacing dimension-theory by two new tags is discussed, I will save here the tag-excerpt and the tag-wiki.

Xander Henderson

5:12 AM

@Andrews I would say that that tag description in that case is misleading. It would be better phrased as "Möbius transformations, an example of linear fractional transformations..."

Or... "Möbius transformations, sometimes called linear fractional transformations on $\mathbb{C}$..."

It is also worth noting that the tag-description cites Wikipedia (which mentions only Möbius transformation, and does not mentions LFTs), whereas the MathWorld article states that the two terms are synonymous (via a citation to Apostol).

I'll repeat my suggestion that the tag "linear-fractional-transformation" be created, and that both "mobius-transformation" and "lft" be pointed in the direction of the new tag.

Martin Sleziak

6:29 AM

Just to save it somewhere, here are the two versions of the tag-info for semisimple-lie-algebra(s). The original one created by Andrews': math.stackexchange.com/posts/3179233/revisions math.stackexchange.com/posts/3179232/revisions And the second one created by Xander Henderson: math.stackexchange.com/posts/3193528/revisions math.stackexchange.com/posts/3193527/revisions

Martin Sleziak

7:32 AM

I am not sure that I have ever actually seen a question about topological dimension theory. That is not to say that such a thing doesn't exist---I just don't think that it comes up all that often. — Xander Henderson 16 hours ago

Re: I am not sure that I have ever actually seen a question about topological dimension theory. Depending on the viewpoint, some people might count there also questions about Hausdorff dimension or some other types of dimension that you have mentioned. But definitely these ones: Lebesgue covering dimension, small and large inductive dimension — Martin Sleziak 3 hours ago

@XanderHenderson This is only a very rough comparison, but still: There area 75 questions tagged dimension-theory+fractals and 78 questions tagged dimension-theory+general-topology.

Andrews

3

A: Tag management 2019

Proposal: create "linear-fractional-transformation", and synonymize with lft and mobius-transformation. They refer to the same thing in most basic cases. Tag lft is really hard to notice its exsitence, and it only has 16 questions for almost 6 years. Here's some discussion about this.

3

A: Tag management 2019

Proposal: rename "singularvalues" to "singular-values" There's no usage guidance and tag wiki yet.

Martin Sleziak

BTW should we add a comment template to the list of comment templates for incorrectly used tags also for (dimension-theory) (with explanation that it's not for dimension in linear algebra)? Or should we wait first to see how the discussion about splitting the tag pans out?

Andrews

I think so, and I never noticed this post "comment templates for incorrectly used tags " before.

Arnaud D.

8:11 AM

@Andrews Yes, it's a good idea to remind me of this. I created the first tag because there was a good occasion, but I've been a bit busy afterwards, so I left the second one for later.

Martin Sleziak

Just realized that GEdgar wrote a book which includes both the topological dimension and the Hausdorff dimension. It would be great if he can say something about this current issues. — Arctic Char 1 hour ago

@GEdgar There is ongoing discussion on meta about the (dimension-theory) tag. This topic seems to be related to fractals, too - and as you are one of the local experts in this area, if you have some comments on the (dimension-theory) tag, we would be grateful for your input in that discussion. — Martin Sleziak 39 secs ago

Arnaud D.

But now I've created the tag, suggested a tag-wiki and excerpt, and retagged the five questions mentioned by Martin earlier today.

Martin Sleziak

@MarkMcClure The above comment is also intended for you - clearly as the top answerer in the fractals tag, you might also have something to say on this.

@ArnaudD. Thanks for doing that.

new-tag So now there is accessible-categories tag and it also has a tag-excerpt.

Arnaud D.

@MartinSleziak And thank you for approving the edit ;)

Martin Sleziak

I wonder whether we should also notify user122424 who created the previous instance of the tag - which was later deleted. But probably the fact that his questions were edited to include the tag is a notification enough.

Perhaps we can wait a bit to see whether somebody objects to the newly created tag - but I'd guess the post in the tag management thread can be marked as resolved if no objections are raised in the next day or two.

@YuiToCheng I have noticed your recent edit on the intersection-theory tag-info. math.stackexchange.com/review/suggested-edits/1188619 math.stackexchange.com/posts/1273860/revisions I wonder whether we should also include (elementary) set theory to that warning.

I'd guess that this tag is sometimes used for questions about intersection of sets - for example, at the moment there are three questions tagged intersection-theory+elementary-set-theory.

YuiTo Cheng

8:23 AM

@MartinSleziak Perhaps, but there are way more mistagged questions in linear-algebra and geometry

Martin Sleziak

Ok, I'll leave it as it is - we'll see what other users in this room say about this.

BTW in the comment template we have included set theory.

Arnaud D.

@MartinSleziak I've left a comment to notify the creator and suggest they check whether some of their old questions need to be retagged.

I've now recreated the tag "accessible-categories". If you want you can add it to your other questions on this topic, and the same for locally presentable categories (but don't retag too many questions at once). — Arnaud D. 2 mins ago

Martin Sleziak

> The tag (intersection-theory) is for the question about a branch of algebraic geometry called intersection theory. It is not for questions about intersections of sets, calculating intersections of two lines and other similar questions.

Arnaud D.

I will add a link to this discussion to chat. I will stress that both above comments suggest merging those two tags, but not making a synonym. I just wanted to state this explicitly. (Although it is implicit in the comments by GEdgar nad Mark McClure - at least if I understood them correctly.) — Martin Sleziak Apr 5 '17 at 13:46

@MartinSleziak Sorry if this is a stupid question, but is there a difference between merging tags and making a synonym?

Oh wait I've found the answer : math.meta.stackexchange.com/questions/11162/…

I should have searched first. Sorry if I bothered you.

Martin Sleziak

8:55 AM

@ArnaudD. This answer also gives some useful insight into merging tags: What happens with the tagged questions when a tag-synonym is cancelled?

Martin Sleziak

9:21 AM

@Andrews I went ahead and edited the list of comment templates.

@YuiToCheng It goes without saying that if you have some suggestions how to improve the comment template for (intersection-theory), do not hesitate to edit it.

YuiTo Cheng

12:03 PM

Seemingly nothing has been done after the thread How to discourage users from using the “functions” tag.

It's unclear to me what questions should be tagged functions from the tag excerpt and tag wiki

Martin Sleziak

12:24 PM

I certainly agree that the usage of the tag is unclear (and there is probably no consensus on when should be used).

As I said in the comments in that discussion, one type of question which IMO seems to be a good fit for the (functions) tag are the questions about image, preimage, range, and similar topics.

When Asaf Karagila asked "Can we please have a “deprecated tag” feature?", he cited analysis and functions as possible examples.

YuiTo Cheng

I agree with questions like Overview of basic results about images and preimages fits the tag description. But this is not the case for most questions.

Xander Henderson

1:10 PM

@MartinSleziak That's good to know. However, looking down the list of questions marked with both dimension theory and general topology, it seems that most (though not all) of them are concerned with the properties of metric spaces and fractals.

There are one or two questions on analytic geometry.

Martin Sleziak

2:18 PM

@XanderHenderson Well, it's possible that we mean basically the same thing when you use the name analytic dimension theory and I use the name topological dimension theory.

However, there certainly are questions about inductive dimension or covering dimension. Maybe some of them are missing the (dimension-theory) tag.

Xander Henderson

@MartinSleziak Yeah, I don't think that we really disagree.

In any event, I would argue that questions of topological dimension are generally motivated by questions from analysis, and that topological dimension theory is not a rich or well-studied enough field to currently require its own tag. That is, "dimension-theory-analysis" and "dimension-theory-topology" overlap quite a lot, and don't require two separate tags.

And "dimension-theory-analysis" is the more 'active' field, so should give the name to the tag.

And even looking down the list of posts containing "inductive dimension" and "covering dimension", a very large proportion of them are about fractals and metric spaces.

Well, okay, after page one, maybe not so much. :\

Honestly, I just want to be able to follow some version of the "dimension-theory" tag, and read only the kinds of fractal-ish (and related) questions which are interesting to me. I don't want to be reading about Krull dimension or vector spaces.

Have you pinged Marc McClure about this?

Martin Sleziak

2:46 PM

@XanderHenderson I believe I did: chat.stackexchange.com/transcript/message/49993083#49993083

Xander Henderson

6:28 PM

@MartinSleziak Excellent! You are, as always, on top of it. Thanks for your work.

Martin Sleziak

7:51 PM

new-tag Two new tags chain-complexes and shuffles created by Javi.

0

Q: How to combine shuffles

I've got a problem related to $(p,q)$-shuffles that comes from the Eilenberg-Zilber map $\nabla$ when I tried to show that this map is associative in the sense that $\nabla(\nabla\otimes 1)=\nabla(1\otimes \nabla)$. On one side, I have for $(p,q)$-shuffles $(\mu,\nu)$ and $(p+q,r)$-shuffles $(\...

Transcript for

$Mathematics$ Tagging