Talk:Affine symmetric group

Beautiful article

Beautiful prose quality and attention to detail, here, with great illustration. I came across this in the GAN queue; even though I studied quite a bit of algebra, I am not in a position to determine whether the article meets the criteria. (I have no experience in combinatorics.) Good work!

The only thing I can offer is to suggest that there be some motivation for calling it ${\widetilde {S}}_{n}$ rather than another name. (${\widetilde {S}}_{n}$ contains ${S}_{n}$ as a subgroup, as you explain later, but not when it is first introduced.) But that may be hard to do in a way that preserves prose quality and flow, so feel free to ignore. Urve (talk) 23:25, 28 April 2021 (UTC)

Hi Urve, thanks very much for the kind words! About the notation ${\widetilde {S}}_{n}$, first let me say why this is what I chose (which I think you understand already): by far the most common notation for the (usual, finite) symmetric group is $S_{n}$ (sometimes rendered with the S in other fonts, like ${\mathfrak {S}}_{n}$; other options are mentioned at Symmetric group, and I've even seen other random things like γ in some sources). When there are "linear" (or finite) and "affine" versions of some object (like a Coxeter group), it seems very common to denote the affine one with a tilde on top (but again this is not universal; sometimes one sees a hat used, or for authors for whom the affine object is the "natural" one they might write W for the affine version and W₀ for the linear version). So the notation ${\widetilde {S}}_{n}$ is taking the intersection of these two common choices, and is widely in use in the literature. I should be clear that these are my observations from reading sources -- I do not recall seeing anyone write down anything about the choice of notation. I am reluctant to put something like this discussion (that I believe may not be stated in any reliable source) into the article. However, perhaps your point is not that I should add text about why this notation is used, but instead that if I introduce the reader to the fact that the symmetric group is called S_n earlier, that by itself would be helpful? Thanks again, JBL (talk) 16:36, 29 April 2021 (UTC)

That makes a lot of sense, JayBeeEll. Since this is a/the traditional way of writing the affine symmetric group, and it's not explained in the literature explicitly, you are right to be uncomfortable to add it to the article -- it would of course be original. I don't think mentioning S_n being the symmetric group earlier would be too helpful. I suppose I was just confused, not having much experience in this particular area, as to why a tilde was used here - but that appears to be because of my lack of exposure. :) Best of luck, I imagine you'll pass GAN with flying colors and I look forward to seeing other content you contribute to the project. Urve (talk) 02:05, 30 April 2021 (UTC)

That makes sense -- thanks again for your feedback! --JBL (talk) 15:53, 1 June 2021 (UTC)

Short exact sequence

In the "Relationship to the finite symmetric group" section, should there be some mention of the short exact sequence $$0\to \mathbb {Z} ^{n-1}\to {\widetilde {S}}_{n}\to S_{n}\to 0$$ where the first group is the free abelian group of translations, affine permutations that don't permute the residues mod $n$ (with $\mathbb {Z} ^{n-1}$ rather than $\mathbb {Z} ^{n}$ because of the requirement that the shifts sum to zero) and the last one is the quotient from the "As a quotient" subsection? I mean, you sort of do already describe it, but without saying it's a short exact sequence and without stating that the kernel is actually a free abelian group. —David Eppstein (talk) 19:11, 31 May 2021 (UTC)

Freeness is mentioned, but it's snuck in the very last sentence of the section. Perhaps a short additional paragraph on that section, offering the short exact sequence as a summary. Running off to lunch now, but I'll try to find a moment to think about it this afternoon. --JBL (talk) 15:53, 1 June 2021 (UTC)

What about this as a starting point?

The kernel π is by definition the set of affine permutations whose underlying permutation is the identity. The window notations of such affine permutations are of the form $[1-a_{1}\cdot n,2-a_{2}\cdot n,\ldots ,n-a_{n}\cdot n]$, where $(a_{1},a_{2},\ldots ,a_{n})$ is an integer vector such that $a_{1}+a_{2}+\ldots +a_{n}=0$, that is, where $(a_{1},\ldots ,a_{n})\in \Lambda$. Geometrically, this kernel consists of the translations, that is, the isometries that shift the entire space V without rotating or reflecting it. In an abuse of notation, the symbol Λ is used in this article for all three of these sets (integer vectors in V, affine permutations with underlying permutation the identity, and translations); in all three settings, the natural group operation turns Λ into an abelian group, generated freely by the n − 1 vectors $\{(1,-1,0,\ldots ,0),(0,1,-1,\ldots ,0),\ldots ,(0,\ldots ,0,1,-1)\}$.
The relationship of the preceding paragraph may be expressed by the short exact sequence $0\to \mathbb {Z} ^{n-1}\to {\widetilde {S}}_{n}\to S_{n}\mathop {\overset {\pi }{\to }} 0$. Here $\mathbb {Z} ^{n-1}\cong \Lambda$ is the free abelian group with n − 1 generators.

I am not at home so can't easily browse for citations, but I am sure they exist; I am a bit annoyed that neither paragraph has any at the moment. (Also annoying: the Wikipedia LaTeX implementation seems to lose the correct spacing around \to if you use \overset ? Bah.)--JBL (talk) 17:47, 1 June 2021 (UTC)

Looks ok to me. I added \mathop to the formula to space the \to better. —David Eppstein (talk) 18:52, 1 June 2021 (UTC)

Great, thanks! --JBL (talk) 20:33, 1 June 2021 (UTC)

References

@JayBeeEll: I believe the citation format isn't consistent within the article, which may spell misfortune for a GA review. Might want to take a look. Horsesizedduck (talk) 22:11, 6 July 2021 (UTC)

Can you say a bit more? I'm not too sure I understand the problem looking at that guideline. Is it that the citations themselves are inconsistent in style? If so, that's not required. Urve (talk) 02:26, 7 July 2021 (UTC)

Also, what's inconsistent about them? They all appear to use short footnotes with longer references in Citation Style 2. There is one use of "Cor." rather than "Corollary" but that's easily fixed. The {{Academic peer reviewed}} template uses Citation Style 1, but that appears to be more difficult to fix. —David Eppstein (talk) 04:33, 7 July 2021 (UTC)

Sorry, that was dumb of me. I saw parenthetical refs in the text, and numbers and letters in the References section, and stupidly thought "there must be a mistake here". Horsesizedduck (talk) 17:41, 7 July 2021 (UTC)

Horsesizedduck, no worries. Letters are usually for explanatory material that doesn't need to be in the prose proper, so they're more notes than citations. Regarding parenthetical citations: In this article, they use a template. The use of parenthetical style without templates is deprecated (no longer to be used).

If this article did have inconsistent citation style, then it would be a concern. But not for the good article requirements, which does not require it. (Why that is the case I do not know, but so it goes.) Urve (talk) 20:50, 7 July 2021 (UTC)

@Urve: You are seriously mistaken about the format here being deprecated. The use of parenthetical (Harvard) style is deprecated for inline (non-footnote) references. The RFC that led to deprecation of that format did not deprecate its use in footnotes and, as an RFC that was purely about referencing, did not concern the use of the same style as a way of commenting on authors and their publications in article text. The current article uses Harvard-style references in short footnotes, and Harvard-style parenthetical text as a way of talking about authors and their publications within the article text. Neither of those things is deprecated. I would have used {{harv}} rather than {{harvtxt}} for the in-text ones, but that's a minor stylistic choice. —David Eppstein (talk) 21:51, 7 July 2021 (UTC)

David Eppstein, I didn't say it was deprecated here. I said use without a template (like ref, sfn, or harvtxt -- so only bare text, which this article is not) is deprecated. We're on the same page. I only mentioned it for future reference and because they mentioned there was some use of inline references, not that the relevant deprecation was applicable here. Urve (talk) 03:47, 8 July 2021 (UTC)

GA Review

This review is transcluded from Talk:Affine symmetric group/GA1. The edit link for this section can be used to add comments to the review.

Reviewer: Daniel Case (talk · contribs) 03:49, 26 October 2021 (UTC)

OK.

This article has sat unreviewed for six months now, likely because it's about an arcane (to most of us) math topic.

I am not a math person at all, but ... it does not look like we can let this slide any longer. I owe about four reviews, and the type of a person I am, I prefer to take the harder reviews that are always in the top bar (not least because some of my nominations have ended up there; in fact one is there as I type.

So, I will do what I usually do ... print it out, do a light copy edit (to the extent possible for me here) and come back within a week's time with my thoughts based on the article's structure and non-math aspects. I will probably ask at WT:MATH for someone not involved with the article to take a look at the math and let me know how solid it is.

Hey, we should all try to stretch ourselves and push the limit on what we think we can do ... Daniel Case (talk) 03:49, 26 October 2021 (UTC)

Comments from JayBeeEll

Thanks very much Daniel Case for starting this review, and for your initial efforts! I will begin addressing some of the citation needed tags soon. However, there were three of them I wanted to discuss: the one at the top of Affine symmetric group#Definitions, the one at the top of Affine symmetric group#Relationship to the finite symmetric group, and the one at the end of Affine symmetric group#Combinatorial definition. The first two are summary sentences of the subsections that follow them -- they are not meant to be free-standing factual claims, but rather navigational aids that briefly give the reader an overview of what is coming. I would have thought that they did not need independent citations (for the same reason that the introductory section of articles does not). (I mean, I suppose that I could copy some lower-occuring citations up to these sentences, if you thought that would be better.) The third example is a sentence about navigating the article -- it tells the reader that we have introduced X and we have introduced Y and where in the article to find the relationship between them. It has no factual content to cite. May I remove it? Or, is there some way I can reword that you think might avoid confusion here? Thanks again, JBL (talk) 18:01, 28 October 2021 (UTC)

@JayBeeEll: I know how you feel, but I've been dinged myself for this sort of thing (uncited prefatory/introductory sentences) far too many times even though if I had my druthers, too, it wouldn't be necessary. Your proposed solution of moving cites up has always worked for me. Daniel Case (talk) 18:25, 28 October 2021 (UTC)

Great, thanks, I will do that. What about the third one: "The correspondence between the geometric and combinatorial representations for other elements is discussed below in § Connection between the geometric and combinatorial definitions.)"? This sentence has no substantive assertion beyond the structure of the article. Never mind, I see, it's a two-sentence parenthetical. Back to the bookshelf .... --JBL (talk) 23:44, 28 October 2021 (UTC)

Review

OK ... I had meant to get this done over the weekend, but I couldn't, and then I had to work at the polls on Tuesday so that delayed this into the later week.

I am glad to see that editors involved are already attending to the requested footnotes. And, since in the process of reviewing I looked at the original draft on Wikiversity and found the peer reviews there, by People Who Know This Stuff, with advanced degrees, actual academic chairs and all, I will defer to that and consider the math substantially correct, beyond the need for any sort of de novo review. I will say that, with the help of the various links, I was able to follow most of the article on a very minimal, conceptual level. The author(s) are to be commended for that.

I also was grateful for well-written prose, with few grammatical errors and no spelling errors. Nor were any facts repeated, or stated fragmentarily. I would like to think that this is coincident with having to write so precisely, and to a great extent in symbols, about such an abstract and complicated subject. If so, it speaks well of mathematics as a field.

That said, I do think there are some other non-math issues besides the insufficient citations (Before I begin, let me just say that I do understand from writing articles about court cases and legal topics the challenges of writing about an abstract subject, often seen as impenetrable by lay readers, where common usage within the field requires both the use of words used nowhere else in English discourse, and some words that take a nonstandard meaning that cannot be easily intuited from context):

• First, at 60K total, it is long enough that the intro can and should be more than the one graf. This is a common occurrence in GANs I review; usually it stems from someone's efforts to expand the article prior to the nomination and accompanying failure to commensurately expand the intro. But here this is an exception, as it came out of wikiversity that way.

  It seems even to me that at least one, maybe two, more grafs could be added summarizing the sections of the article past the definitions (Consider that the DYK hook fact mentioned the juggling connection ... this is something that should probably have been mentioned in the intro; some DYK reviewers, in fact, insist that the hook fact be in the intro. I don't think that's always necessary and don't insist on it, but here I think it could and should easily have been done).

• This wouldn't be necessary to expand the intro, as it can be done with what's there already, but it might be nice to link from the intro, as soon as possible after the bolded statement of the subject in the lede (from which we are strongly discouraged from linking), to some article, or perhaps the Wiktionary definition, of "affine" so the reader has a chance to understand what it means in this context. Before I started reviewing the article I thought it might have been someone's name (some obscure French or French-speaking mathematician, perhaps? As in so many other sciences, a lot of people leave their mark on the field that way) I was able to gather that it has some meaning that puts it, at least sometimes, in contrast to "infinite", but I would have liked a fuller understanding from the get-go.

  As it is, there is a link that could be made, from the third sentence; while we do have at least a couple of articles that seem like they would provide the necessary explanation I didn't myself feel anywhere near qualified to choose the best one.

Saving ... Daniel Case (talk) 05:15, 4 November 2021 (UTC)

• A lot of sentences in the definitions sections, and indeed throughout the article, use "one" in the third-person impersonal style. I do not know if this is standard in mathematics—if it is, and we use it in other math articles, and we're OK with doing that in math articles, and I can be shown examples, I drop any perceived objections. However, I have seen it nowhere else on Wikipedia.

  Yes, MOS:YOU explicitly does not rule out this use. But it also suggests that such use should be limited only to situations where that is really the only way to do it, and I'm not sure we have that here. I also note that MOS:MATH#NOWE strongly suggests that the use of pronouns to address the reader should be avoided.

  In other words, is it possible to rewrite or recast those sentences such that we don't have to use "one"?

• And per the above, "To translate between the geometric and algebraic definitions, fix an alcove and consider the n hyperplanes that form its boundary" is in the imperative. That's common in a textbook, but we generally try to avoid that in an encyclopedia.
• One thing that might help make for a longer intro is something many of our other conceptual math articles that have gained at least GA have: a brief history section explaining how the concept came to be discovered or something like that. This article IMO could use one. As it is it just seems as if the idea of affine symmetric groups just appeared on a stone tablet lowered from a flying saucer by a beam of light. Surely this is not the case ... a reader would get a better handle on the subject understanding where it came from, who (if they are notable) developed and perhaps named the concept, when, and where. And maybe they won an award for doing this.

  At the very least it would provide a brief respite from the equations and diagrams, especially if there is the potential for it to be illustrated by the inevitable image of some dead old white guy, either painted in academic regalia or photographed in black and white staring intently at the camera.

• Might those parentheticals at the end of a couple of grafs be better off converted into endnotes using {{efn}}? They sort of read that way to me.
• There are also a fair amount of free-standing single-sentence grafs. Per MOS:PARA we should try to combine them with adjacent, longer grafs, unless there is a good reason not to.
• I actually seemed to have been right before this partial revert. Going back to the above link to MOS:MATH, it explicitly says that "When defining a term, do not use the phrase 'if and only if'." Some of the other guidance there is on point.

Saving again ... Daniel Case (talk) 05:47, 4 November 2021 (UTC)

• Starting at "cycle type and reflection length", the article inexplicably begins using its Harvard references not only inline and within sentences, but as nouns, or stand-ins for the papers being referred to, rather than at the ends of sentences as sources only visible on mouseover as we typically do, regardless of the citation style being used. This, again, recalls a common issue in GANs for me, in which it is often possible to detect the involvement of different writers at different times due to subtle and not-so-subtle changes in focus and style, often in citations ... in other words, the nominator didn't go through the whole article after expanding it to make sure the voice was consistent. But, again, that is clearly not the issue here, since the article's voice is the same throughout.

  So, honestly, I don't know why this was done here. But, and I must speak more boldly than I have otherwise in this review, it must be undone. We can't have two different cite styles within the same article.

  And you have no choice of which style to adopt. It must be undone to be consistent with the citations in the first half of the article. I see nothing in WP:HARVREF suggesting that citations can be used this way, and given that per WP:HARVARD we deprecated inline parenthetical refs a little over a year ago, there is no justification for doing things this way. Put them in tags and rewrite or recast the sentences. This is the most essential thing in this punch list after getting all the material properly sourced.

  • Comment. Much of your review is helpful, but I wanted to comment on this part. I do not agree with the view that the Harvard references here are deprecated since they are not references in the Wikipedia sense, but are used to refer to specific works. Writing "Smith wrote in 1999" and "In (Smith 1999)" are essentially the same and don't appear (to me) to be the deprecated style, since it is merely a way of writing names, not a way of citing sources for specific information. Now, this does raise an interesting question - should the "Representation theory and an affine Robinson–Schensted correspondence" section have references, or is the textual clue that they refer to specific works enough? Dunno, but something to think about. Also, even if it were a citation style, consistency in citation styles is not required by the GA criteria. (Deprecation is a separate issue.) Urve (talk) 09:06, 4 November 2021 (UTC)

    Harvard references used inline are deprecated. There's no problem with them in footnotes, like the former of the two variants you proposed above.

    You are correct in that the good article criteria do not explicitly require a consistent citation style throughout the article, but ... I would commend your attention to WP:CITESTYLE, which does say: "citations within any given article should follow a consistent style." This to me is an implicit requirement that does not and should not need to be restated (even though, of course, it is in the featured article criteria). Daniel Case (talk) 19:06, 5 November 2021 (UTC)

• If J.Y. Shi's notability can be demonstrated, start at least a stub article. Otherwise delink his name.
• I think the juggling patterns illustration, given its long strip-like shape, would look better centered above the text, rather than off to the side sticking into the main text awkwardly, twice as wide as any other image. I did something sort of similar here.
• And to complement a history section, I wonder if it might be possible to end briefly talking about the future: What's going on in research into affine symmetric groups? Are any interesting possibilities opening up? Any new questions to be answered? Maybe something like that.

And that's it. I think these issues can reasonably be addressed within the usual week or so, and of course I can extend that time limit if it looks like you're making progress. So, I'm putting the article ...

 On hold

Happy editing! Daniel Case (talk) 06:14, 4 November 2021 (UTC)

Response

Hi Daniel Case, thanks very much for this review, both the positive feedback and constructive criticisms. I plan to respond in stages over the next several days. An initial version (with some bolded quotes of your comments and my interspersed responses) is below.

First, at 60K total, it is long enough that the intro can and should be more than the one graf.

Yes, absolutely I agree, I will work on it. I have added two short paragraphs to the introduction; together, I believe they mention the highlights of all major body sections of the article. I'm going to call this  Done for now. JBL (talk) 12:17, 9 November 2021 (UTC)

it might be nice to link from the intro ... to some article, or perhaps the Wiktionary definition, of "affine"

Ok so on one hand this point is obviously correct, and I would like to write a sentence (or maybe footnote) that explains it. (The ultimate explanation is that affine geometry is a certain perspective on the study of geometry that focuses on collinearity (when points are on the same lines) and parallelism; the geometric transformations (like rotations, translations, reflections) that preserve these properties (so if several lines are parallel, they get transformed into new lines that are still parallel, etc.) are called affine transformations, and in the geometric construction of the affine symmetric group the elements are all affine transformations. The article Affine transformation gives an etymology. I would write something shorter than the preceding if I write something.) On the other hand, I don't have any source for what I just wrote: it's a cobbled together synthesis from sources that don't mention the affine symmetric group at all, plus my personal understanding of how mathematicians use words. So I'm concerned about how to go about this in practice. Thoughts or suggestions are welcome. --JBL (talk) 11:48, 10 November 2021 (UTC)

A lot of sentences in the definitions sections, and indeed throughout the article, use "one" in the third-person impersonal style. ... is it possible to rewrite or recast those sentences such that we don't have to use "one"?

Ha, gosh, and I was so proud of myself for avoiding "we" (first-person plural is standard in mathematical papers, even when written by a single author). I see about 15 uses of "one has", "one may", etc. -- some are clearly avoidable, I'll see what I can do with them. I have significantly reduced the number of these; let's call it  Done for now. --JBL (talk) 11:48, 10 November 2021 (UTC)

history section

Yes, more historical information would be good. I note that I haven't written down anywhere that the combinatorial definition of the group was first given by Lusztig in 1986, for example. I am not sure whether it will be possible to source a full section's worth of historical content to reliable sources; for example, I don't know whether Coxeter ever singled this group out for particular attention in his work. Unfortunately searching that out will take more time than I have available in the near future. (It is possible that in some sense the history of this object studied for its own sake rather than as one example of an important family only dates back < 40 years.) --JBL (talk) 11:48, 10 November 2021 (UTC)

I have made a first attempt at this, so let's say  Done for now. I believe it would be possible to write a more detailed history section on affine Coxeter groups in general, but I am skeptical that there is a lot more to be said about the affine symmetric group in particular. --JBL (talk) 14:49, 15 November 2021 (UTC)

There are also a fair amount of free-standing single-sentence grafs.

This was particularly the case in the section Affine symmetric group#Descents, length, and inversions, for whatever reason -- I have merged related consecutive single-sentence paragraphs there into larger paragraphs.  Done JBL (talk) 12:17, 9 November 2021 (UTC)

I actually seemed to have been right before this partial revert. Going back to the above link to MOSMATH, it explicitly says that "When defining a term, do not use the phrase 'if and only if'."

You are right about what MOS:MATH says, but wrong in this instance that it applies. That portion of the MOS is about definitions; for example, in the section Affine symmetric group#Combinatorial definition, the second sentence says "a function u is an affine permutation if [some conditions hold]." The admonition in MOS is that I should not have written "a function u is an affine permutation if and only if [some conditions hold]". But the statement about permutation patterns is not a definition. JBL (talk) 12:17, 9 November 2021 (UTC)

OK, no problem ... I defer. Daniel Case (talk) 18:50, 5 November 2021 (UTC)

Harvard references

The mention of multiple authors amused me, because really this is my individual work (of course with several improvements by other editors since it went live). Though it's not necessary to address the issue you raised, I thought I would take a swing at explaining. Mathematical journal writing often varies between the two modes of stating things without the context of where it came from ("the affine symmetric group is ...") versus attributing particular ideas to particular people ("Shi showed that ..."). I'm not sure I can exactly justify each choice about which fact gets introduced which way, but roughly I think the division is between "folklore" and "things everyone knows" (esp. in the context where you might write a background section of a paper and begin, "for more information on these topics, see [standard textbook or reference work in the field]" somewhere at the beginning) on one hand, and things that are more recent, have only appeared in the original research papers (rather than being re-exposited elsewhere), etc. One might hope that mentioning particular authors also gives a sense of the dynamic of the field (something that you have noted was not otherwise conveyed well -- though now with a history section it's a bit better).

Now let me move towards addressing the point. There was a discussion about this on the article talk-page, and Urve commented on it above. My view is that I'm using Harvard references in order to mention, in the text, the authors of particular works, along with pointers to those works. Some uses are unambiguously of this form (e.g., the first sentence of the section on juggling sequences). But I do agree that I'm maybe trying to have it both ways in some places, where I'm mentioning individual authors or papers and not also citing those mentions to other authors or papers. I think I'd like to try to reach an agreement about which places current usage is acceptable (e.g., I feel strongly that this is the case for the section on juggling sequences) and which are not (I think Urve has a point that the section on Representation theory and an affine Robinson–Schensted correspondence is pushing the boundary here, and maybe the section on Fully commutative elements and pattern avoidance as well) before I patch them. --JBL (talk) 12:25, 16 November 2021 (UTC)

And per the above, "To translate between the geometric and algebraic definitions, fix an alcove and consider the n hyperplanes that form its boundary" is in the imperative.

I have (temporarily) converted from the imperative to the third person, to be further resolved when I think about the rest of the "one can"s. So let's call this specific point  Done

Might those parentheticals at the end of a couple of grafs be better off converted into endnotes using {{efn}}? They sort of read that way to me.

This is a chronic flaw in my writing.  Done (I think). JBL (talk) 12:17, 9 November 2021 (UTC)

J.Y. Shi

I am querying someone with more WP:NPROF expertise for their opinion on this question. So based on David Eppstein's comment here I believe that Shi probably is notable. However, I'm not going to write an article about him in the near future, so I have removed the link.  Done --JBL (talk) 14:49, 15 November 2021 (UTC)

I think the juggling patterns illustration, given its long strip-like shape, would look better centered above the text

Yes, nice suggestion, and thank you for showing me how it can be done.  Done JBL (talk) 12:17, 9 November 2021 (UTC)

And to complement a history section, I wonder if it might be possible to end briefly talking about the future. What's going on in research into affine symmetric groups? Are any interesting possibilities opening up? Any new questions to be answered? Maybe something like that.

This is a nice suggestion but I think it would be impossible to source to secondary sources. (I could, like, go pull a bunch of conjectures and open problems from recent papers, but I think it would be impossible to justify any particular choices and avoid synth.)

OK; it was just an idea. Daniel Case (talk) 22:56, 15 November 2021 (UTC)

It is a nice idea! I wish there were more people writing the kind of expository / state-of-the-field articles in mathematics that could be used for this. --JBL (talk) 12:25, 16 November 2021 (UTC)

@Daniel Case: Thank you for your patience. I have completed a first run through at addressing or responding to your comments. I would be interested in your assessment of this progress. Thanks, JBL (talk) 12:25, 16 November 2021 (UTC)

@JayBeeEll: So far so good. I was wondering ... now that we've expanded the intro, is there any image in the article we could put in the intro as lede image? If not, is there one somewhere else? Can one be created relatively easily. Daniel Case (talk) 07:05, 18 November 2021 (UTC)

@Daniel Case: Well, the natural thing is the triangular tiling of the plane; I went and found one on commons with some color in it. --JBL (talk) 00:23, 28 November 2021 (UTC)

Looks good ... we got some Joker action going there! Daniel Case (talk) 06:35, 30 November 2021 (UTC)

The only thing I'm a little worried about with this image is that symmetries of the tiling itself and symmetries of the colored tiling are not the same thing. —David Eppstein (talk) 08:21, 30 November 2021 (UTC)

@David Eppstein: Is this something that can be easily fixed? Daniel Case (talk) 06:04, 2 December 2021 (UTC)

Only by using a much less eye-catching image like File:Uniform tiling 63-t2.svg. I'm not sure it's really much of a problem. Anyone who would notice that it's an issue would also know to ignore the colors for sake of the example. —David Eppstein (talk) 07:12, 2 December 2021 (UTC)

Oops, I could have sworn I responded here yesterday, but it seems I never hit "publish". I did think about this a little when choosing the figure, and decided the risk of confusion was low. The figure DE linked is the one I would have chosen instead. --JBL (talk) 15:35, 3 December 2021 (UTC)

Christmas greetings

@JayBeeEll: Merry Christmas (two days late) and Happy New Year! Holiday greetings aside, I see that you have not been able to do any work on this article in a month. I know you're an academic and this is a busy time of year. Will you be able to resume after the holidays? Daniel Case (talk) 01:04, 28 December 2021 (UTC)

Hi Daniel Case, thanks for the ping and the holiday greetings -- the same to you! (I was up vaguely in your corner of the world for Thanksgiving -- took the wonderful Amtrak line along the Hudson, visiting family in Columbia County.) Yes, this really fell off my radar as end-of-semester hecticness set in. Is it possible to get a revised sense of what issues you view as unaddressed / essential to be resolved? For example, I have marked some things as "done" above, but it is not clear to me if they are done to your satisfaction. (I realize there are still a number of cn tags in the article, as well.) Thanks very much, JBL (talk) 00:44, 29 December 2021 (UTC)

Sure, it may take a while, but I'll get back here. Generally you're more than 50% done ... if I could suggest anything right now, it would be making sure everything that isn't currently cited is. Daniel Case (talk) 05:39, 31 December 2021 (UTC)

@JayBeeEll: Alright. Looking everything over, I think all that's left is the six places where {{fact}} tags remain. Fix those and we're pretty much (ahem) good. Daniel Case (talk) 22:54, 4 January 2022 (UTC)

@Daniel Case: That's incredibly helpful, thanks. I was able to get into my office yesterday and pick up some books; I will put in a final push this week and ping again soon. --JBL (talk) 01:53, 5 January 2022 (UTC)

@Daniel Case: Thanks again for all the work you've put into this. The current status is as follows: I have provided sources for factual claims as best I can; I've removed some material that ultimately I have not been able to adequately source. There are two cn tags still in the article. The rest of this comment is an argument that they should be removed (without any changes to the text).

Both remaining cn tags concern the following situation: there are multiple valid conventions in the literature about how to present, display, or denote something; while each is separately valid, the conventions are incompatible with each other, and so any given expositor is forced to choose one of them. (For example, one could choose to number the rows of a matrix so that the indices increase from top to bottom, or one could choose to number them so that they increase from bottom to top.) Both sentences that are tagged explain to the reader what convention is being used in this article. This is essential information (otherwise it leaves ambiguity as to which of several incompatible choices has been made), but it is impossible in principle to cite it (because they are statements about this article itself). I suppose for the first one I could remove the figure (thereby removing the need to explain what convention is being used in the figure), but the second one seems completely unavoidable to me. Any thoughts or comments you had are welcome. --JBL (talk) 00:57, 7 January 2022 (UTC)

@JayBeeEll: Oh ... OK ... I see what you're saying and I hear you.

These cats can be skinned in different ways.

For the first one, you're leaning on WP:OI. Technically, you'd say you don't need any citation, and in a better world I'd agree with you, and that would be it. But ... since we're not in a better world, I'll recommend instead what I've done for years since someone at a DYK nom accepted OI but insisted I find some way to cite it: <ref>See accompanying diagram</ref> (Or whatever term for the image works best for you).

As for the second one, I think, I typically put such meta references of the "In this article ..." type into {{efn}} endnotes. I think that would work here, and then the remaining sentence could be joined into the next graf. Daniel Case (talk) 04:59, 10 January 2022 (UTC)

@Daniel Case: can you please re-read the actual good article criteria, paying very careful attention to exactly what it says about sourcing? Note in particular that it is much less strict than the DYK sourcing rules, which themselves require only a single footnote per paragraph. The relevant rules for GA are 2b, which does not say anything about what should be referenced, only that when things are referenced their sources should be reliable, and 2c, which says in its entirety "it contains no original research". Not that all content is actually sourced to anything, but merely that it is known material rather than something entirely made up as new material for the Wikipedia article. On what basis of GA rules are you making these bizarre demands that material that merely explains the structure of the article itself must somehow have a footnote and that this footnote requirement would be satisfied by putting something inane and non-referency into the footnote? In what way do any of these statements constitute original research? Wouldn't putting an inane non-citation into a reference violate 2b, which requires that the references be reliable sources? How do you read the rules as in any way causing such a requirement to exist? What words of the rules are you following in this? —David Eppstein (talk) 05:32, 10 January 2022 (UTC)

@David Eppstein: What harm could it possibly do to the article? If you'd like to have someone else review it, I'd be happy to let it go and have them take a crack at it. Daniel Case (talk) 05:37, 10 January 2022 (UTC)

The harm is not primarily to the article, but (1) to the Good Article process caused by your dragging out this review endlessly with demands for additional footnotes where no footnote is needed and where none of the GA rules justify such a demand, (2) the creep to GA rules caused by your inventing rules out of thin air, and (3) the damage to encyclopedia content creator goodwill caused by your turning what should be a much more straightforward evaluation process into a bureaucratic nightmare. Anyway, is there a reason why you haven't answered any of the questions in my previous comment? —David Eppstein (talk) 05:40, 10 January 2022 (UTC)

Because I'm done with this review right here and right now, that's why. Daniel Case (talk) 05:59, 10 January 2022 (UTC)

For what it's worth at this point, I agree with JBL. The first CN tagged sentence is just describing the image of the matrix. It's not really making a claim that needs a citation. See for instance the images in addition and their corresponding descriptions; the first image's description there has a citation but I think that's more to support the "popular" claim. In this case (i.e. the article Affine symmetric group) the description is just kind of long and is in the article instead of under the picture.

For the second one, it's just explaining convention which is common (and necessary) in mathematical writing. Since convention is important and using different conventions can be seriously confusing, it may be better to leave it in the article rather than a footnote.

I will say, however, that it took me a bit to understand the image of the matrix since it uses dots for 1s and omitted zeros and lacks borders for individual rows and columns (if I understand it correctly, the lines delimit each group of three rows and columns). I know it's probably to give a more geometric flavor to the image so that you can see a pattern, but yeah. For reference, I studied math in undergrad, so it may be confusing for those even less mathematical training (though I suppose most readers of this article will have some). Perhaps an image that requires less explanation can be used, or the image might be omitted altogether as JBL suggested. Winston (talk) 10:43, 10 January 2022 (UTC)

Hum, well, Notsniwiast, I think your comment has convinced me first that the description of the image should really be in the image caption, not in the text. (The reason to display the matrix this way is that if you don't, it's very hard to see the isolated 1s in a huge sea of 0s -- several references make the same choice, presumably for the same reason.) Do you think it would help if I added row and column numbers along the outer border of the matrix? --JBL (talk) 21:12, 10 January 2022 (UTC)

I tried a thing but it did not work well so I self-reverted. May try again later (1st day of classes is tomorrow) .... --JBL (talk) 21:15, 10 January 2022 (UTC)

Yes I think adding row/column numbers may help, and would also allow the description to be shortened. Winston (talk) 02:35, 11 January 2022 (UTC)

@Notsniwiast: Indeed! It is done. --JBL (talk) 02:05, 14 January 2022 (UTC)

This looks better to me too. I might quibble that the rectangular rather than square aspect ratio of each matrix cell, and pixel graphics rather than vector graphics, are both suboptimal, but those are minor quibbles that shouldn't affect the discussion here, and they may be difficult to change depending on how you're generating the image. —David Eppstein (talk) 02:09, 14 January 2022 (UTC)

@David Eppstein: Hmm, I hadn't noticed that they're not perfect squares, thanks -- I've fiddled, now it's better. I am using LaTeX -> PDF -> PNG to produce images (same as for all the others I created in the article); if you know how to get SVG output from LaTeX, I'd be happy to hear about it! --JBL (talk) 01:49, 16 January 2022 (UTC)

There are several ways of getting svg from pdf, but I'm not sure which of them if any play nicely with the LaTeX fonts. The workflow I use for that (opening in Adobe Illustrator and saving as svg) definitely doesn't work well with those fonts. Maybe someone else knows? —David Eppstein (talk) 01:53, 16 January 2022 (UTC)

Status query

JBL, David Eppstein, where does this review stand? It seems clear that Daniel Case has stepped back from reviewing; has David Eppstein taken over, or do we need to find a new reviewer? If the latter is the case, then the nomination should probably be set to request a second opinion, in the hopes that someone who can deal with the arcane mathematics text will be able to take over. (Or perhaps a request should be made at WT:GAN?) Thank you. BlueMoonset (talk) 05:42, 16 February 2022 (UTC)

I have edited the article too much to take over. The mathematics has all been reviewed; the only sticking point was that Case was demanding citations for sentences like the one in this diff, which merely stated which of multiple notational conventions the article was following, and refusing to back down from that demand after multiple editors tried to intervene. However, Case's responses to why he was refusing to back down did not make me confident in the depth of the rest of the review: as far as I can tell it amounted to checking sourcing by whether there were lots of little blue numbered footnote markers and not by whether the material needed sources and whether the sources were adequate for the material. —David Eppstein (talk) 06:54, 16 February 2022 (UTC)

Failure to assume good faith like this is why I am not interested in finishing this review. "Multiple editors" did not try to intervene on Eppstein's behalf; in fact if there were any actions by multiple editors that might have served as effective intervention had they been more willing to take action (a reluctance I now fully understand) it was the many supportive emails I got from other participants in the math project about dealing with Diamond Dave here.

I had thought my willingness to take on a GA review in this subject area, especially an article which I remind Dave had languished for months before anyone dared review it, might have been appreciated, and indeed it was, by every other editor who was working on the article.

Yes, I'm not a higher level mathematician, so I relied on the critiques of the math sourcing in the WikiJournal of Science, which seemed to me to be rigorous enough. Again, I think anyone looking for a review of an article that had been languishing at GAN unreviewed for six months should be grateful someone went and reviewed it at all rather than raising side-eyed comments about "the depth of the review".

As for his comments about "checking sourcing by whether there were lots of little blue numbered footnote markers and not by whether the material needed sources and whether the sources were adequate for the material", well, Dave, you need to get out of the math ghetto more. This is exactly the criterion by which GANs in every other subject area are reviewed. I commend to your reading attention this:

It is possible that an editor who is trying to promote an article to GA-class (good article status) might add citations to basic facts such as "...the sky is blue...". This is a good thing, and the fact that the sky is not always blue does benefit from adding a citation. We can add citations for things that are well-known, and the source can contain additional information to benefit our readers.

And there is also this section hed: "It's easier to find a citation than to argue over why it is not needed".

JBL had been willing to meet me halfway on this, and I was really just that one issue away from ending the review with a promotion when you had to be the angry mastodon and come in and kick everything over, over a relatively minor issue that you could have handled with much more tact... in fact, any tact at all would have been an improvement.

I also cannot reiterate strongly enough how personally I take your insinuation that I only cared about the existence of citations and not their quality. Assessing the quality of the sources here may have been beyond my depth, as I've said (and to put more crudely what I've said a few times already, beggars can't be choosers). In some other GA nominations I've reviewed, I have queried the reliability of the sources. And I'm sure if I looked through other GA noms I've reviewed, I could find more examples.

To make such a remark so recklessly warrants an apology, but I'm not hopeful. Daniel Case (talk) 08:28, 16 February 2022 (UTC)

Why would I apologize, when your response to my accusation of superficial reference-checking is "This is exactly the criterion by which GANs in every other subject area are reviewed." rather than even the most feeble denial? (Also, please do not call me "Dave"; it is not my name.) —David Eppstein (talk) 16:07, 16 February 2022 (UTC)

So you would have more respect for me if I had lied? I'll keep that in mind next time. If there is one. Daniel Case (talk) 19:19, 16 February 2022 (UTC)

I have made only one edit, and I have not found any serious issues with the article in my reading so far. I'm a physics person rather than a pure-math person, so I'm accustomed to technical prose without being too familiar with the details of this specific topic. Speaking from that background, I think it's a pretty nice page! Kudos to all those who have put serious work into it.

Minor concerns: the manner in which it points to items in the literature is not perfectly uniform. I call this a "concern" rather than a "problem", because I don't think it impedes understanding, and life is too short for me to really care about the distinction between In (Lewis et al. 2019), the following formula was proved and A 2019 paper by Lewis et al. proved the following formula. I see that this has been discussed above, and I think that JBL's desire to mention, in the text, the authors of particular works, along with pointers to those works is legitimate. This is a matter of taste; perhaps the most serious thing I can say about it is that having effectively three citation styles — a footnote to Smith (2005), inline Smith (2005) and also inline (Smith 2005) — is too choppy. This particularly sticks out in the subsection Representation theory and an affine Robinson–Schensted correspondence, where an endnote and both styles of parenthetical all crowd together.

There are a couple redlinks. This isn't a problem with the article itself, but if the content they should point to does exist somewhere, then they should be pipes or redirects. It's probably worth checking. No big deal if they stay as they are, though.

Something about the way the term type A root lattice is introduced and used bothers me a bit. If a reader isn't familiar with the classification of root systems and related topics, dropping type A in like that (and then including it inconsistently thereafter) might be slightly puzzling. "What makes this lattice 'type A'? Do these things also have lattices of other types? What does the type tell me?" Maybe I'd say something like, "... forms a root lattice, specifically one of type A". Perhaps the text or the figure caption could mention that the triangular lattice is known as A₂.

Very short sections often read as unfinished to me. Here, "History" is only three sentences. It's serviceable, and I wouldn't object to a GA having a section like that, but I'd advise thinking a moment or two about whether it could be expanded.

Cheers, XOR'easter (talk) 20:54, 16 February 2022 (UTC)

Hi XOR'easter, thanks for your comments!

In the section on the representation theory, I could easily convert the Viennot reference to a (Viennot yyyy) reference by mild rewriting: "... introduced by Viennot in (Viennot yyyy)." That would reduce by 1 the number of distinct styles in the section. A worthwhile change?

Core partitions are a wonderful combinatorial gadget that I'm surprised no one has written anything about in Wikipedia, but I have looked in all the obvious places and searched in various ways and I just don't think it's here. We have content about parabolic subgroups of algebraic groups, and of course this concept is intimately related to the concept in Coxeter groups, but none of our articles on Coxeter groups (Coxeter group, Weyl group, Reflection group, Dynkin diagram, Coxeter diagram) seem to mention it -- and the article on algebraic groups does not mention the associated Weyl group. Core partitions are probably a central object in dozens of research papers, parabolic subgroups in hundreds or more, so I think notability is not a concern. (Obviously I need to convince some friends to become Wikipedia editors to fix these oversights.)

About type A root lattice, I see that the classification of affine Coxeter groups is not clearly spelled out anywhere in the article -- there are a few spots (when $\Lambda$ is introduced; in the section on Lie algebras; and finally in the section on other affine Coxeter groups) where it is alluded to, but that's it. I can't decide how I feel about this: from the point of view of ${\widetilde {S}}_{n}$, it doesn't matter what type it is, but if you happen to be the kind of person who thinks about reflection groups then of course this is a crucial piece of identifying information. My first instinct is to remove both instances of "type A" from the section you mention, and to add a few words in the section Affine_symmetric_group#Combinatorics_of_other_affine_Coxeter_groups to explicitly mention that type A is the one we're talking about. What do you think?

Finally, about the short history section, if you search above on this page you'll see my comment there that I believe it would be possible to write a more detailed history section on affine Coxeter groups in general, but I am skeptical that there is a lot more to be said about the affine symmetric group in particular. My opinion of this hasn't really changed since then.

Thanks again for your comments! --JBL (talk) 01:02, 17 February 2022 (UTC)

I think reducing the number of distinct styles by 1 would be a slight but noticeable improvement, and since it's a quick fix, it's probably worthwhile. If there's nothing yet that core partition can point to, then leaving it as a redlink is the best thing (as it signals there's a new topic to develop). I like your instinct about the "type A" business. And if there's no obvious way to expand the "History" section, I think it's fine as is. XOR'easter (talk) 02:26, 17 February 2022 (UTC)

@XOR'easter: Thank you! I have made those two changes (Viennot and type A). The wording of the new sentence in the section on other groups is a bit clunky, but I think it does the job. --JBL (talk) 12:28, 17 February 2022 (UTC)

Those changes look good to me. I'm inclined to say the article deserves GA status now. The instructions say Do not close a review started by another reviewer without first attempting to contact the first reviewer, but in this case the first reviewer appears to have distanced from the article. XOR'easter (talk) 20:32, 17 February 2022 (UTC)

@XOR'easter: I have been monitoring this and I'm OK with your decision. Daniel Case (talk) 20:49, 17 February 2022 (UTC)

Thank you for letting me know! XOR'easter (talk) 21:00, 17 February 2022 (UTC)

True statements that I was not immediately able to source

Here I'm going to maintain a (hopefully short) list of things that are true but that I was not able to find sources for on first attempt:

• "In terms of the geometric definition, this corresponds to the reflection across the plane $x_{i}-x_{j}=k$." [1]
• "The non-maximal parabolic subgroups of ${\widetilde {S}}_{n}$ are all isomorphic to parabolic subgroups of $S_{n}$, that is, to a Young subgroup $S_{a_{1}}\times \cdots \times S_{a_{k}}$ for some positive integers $a_{1},\ldots ,a_{k}$ with sum n." [2]
• One may define ${\widetilde {S}}_{n}$ to be the group of rigid transformations of V that preserve the lattice Λ. (D'oh -- this is just false!)
• In terms of the Coxeter generators of $S_{n}$, this can be written as $\pi (s_{0})=s_{1}s_{2}\cdots s_{n-2}s_{n-1}s_{n-2}\cdots s_{2}s_{1}.$
• The relationship between the kernel, the affine symmetric group, and the image of π may be expressed by the short exact sequence $0\to \mathbb {Z} ^{n-1}\to {\widetilde {S}}_{n}\mathop {\overset {\pi }{\to }} S_{n}\to 0$. Here $\mathbb {Z} ^{n-1}\cong \Lambda$ is the kernel, a free abelian group with n − 1 generators.
• The analogous combinatorial construction is to choose any subset A of $\mathbb {Z}$ that contains one element from each conjugacy class modulo n and whose elements sum to $1+2+\ldots +n$; the subgroup $({\widetilde {S}}_{n})_{A}$ of ${\widetilde {S}}_{n}$ of affine permutations that stabilize A is isomorphic to $S_{n}$.
• Full details of the geometry for the infinite dihedral group: who are the roots, what is the alcove.
• The sentence "However for higher dimensions, the alcoves are not regular simplices."

--JBL (talk) 11:30, 4 November 2021 (UTC)

Affine symmetric group review

Dear JayBeeEll I shall write here my comments rather than on your talk page as for some reason this caused your talk page to crash (it had to do with mathjax re-interpreting old stuff from your talk page for some reason). The article looks very good to me, informative and complete. I have a couple of questions/observations:

• There is a whole section on "Relationship to the finite symmetric group" and so I wondered why there was nothing on the relation to the group of braids on $S^{1}$ because as far as I can tell the affine symmetric group is a quotient of the braid group $B_{n}(S^{1})$ of braids on $S^{1}$ under the relations $s_{i}^{2}=Id>$ for all i. Of course this is a simple observation, straightforward from the formal definition but I wonder why this isn't in the article. This quotient is compatible with the projection $\pi$ from ${\tilde {S}}_{n}$ to $S_{n}$, so is $\pi$ also the projection from $B_{n}(S^{1})$ to $S_{n}$ (I think) where it is eminently simple to visualize. The relation to the braid group on the circle makes it easier (to me at least) to visualize the relations of the algebraic definition, in a manner similar to that given here.
• In the section on the combinatorial definition, when you write $\sum _{i=1}^{n}u(i)=1+2+\cdots +n$ I understand that this is easier for the general audience, but perhaps you could add $={\binom {n+1}{2}}$ or $={\frac {n(n+1)}{2}}$ as these forms are commonly encountered in the literature when presenting this result.
• As a Coxeter group (or as a quotient of the braid group), the word problem for the affine symmetric group is solvable. I think this should be stated somewhere.
• In sentence "The generating function for these statistics over ${\widetilde {S}}_{n}$ simultaneously for all $n$ is" you could perhaps add the word "bivariate" in front of "generating" and you can wikilink to Generating_function#Bivariate_and_multivariate_generating_functions
• General question: let's say a reader wants to delve more into the subject, which book shall he/she go to ? Is there no general review book on the topic or are the historical item cited the best there is to be up to date on the notion ?Iry-Hor (talk) 09:44, 5 June 2023 (UTC)
• Ref "Lusztig, George (1983), "Some examples of square integrable representations of semisimple p-adic groups", Trans. Amer. Math. Soc., 277: 623–653" is missing its DOI. Some other references are lacking DOI but have their MR numbers so it is fine by me. You might still get it pointed out at FAC though. Similarly none of the books have the publisher location listed but I think it is fine for FAC if nobody raises this in the sources review. It is actually better to have none than an inconsistent style with some that do and others that don't.
• Two references are only arXiv preprint which might pose a problem at the FA source review. But these preprints have since been published. "Chmutov, Michael; Frieden, Gabriel; Kim, Dongkwan; Lewis, Joel Brewster; Yudovina, Elena (2018), Monodromy in Kazhdan-Lusztig cells in affine type A" is now published at Selecta Math. New Ser. 28, 67 (2022) and "Monodromy in Kazhdan-Lusztig cells in affine type A; Michael Chmutov, Joel Brewster Lewis, Pavlo Pylyavskyy" is in Math. Annalen, 2022.

More comments to come.Iry-Hor (talk) 09:44, 5 June 2023 (UTC)

Technical comments for FAC:

• I found a couple of duplinks : infinite dihedral group and identity element are wikilinked to several times in the main text.
• All pictures must have alt text, which you can insert in the code with "| alt =" in the figure caption. This is mandatory for FA, see the MOS.

More comments to follow.Iry-Hor (talk) 11:46, 5 June 2023 (UTC)

• • Note to anyone else interested in this discussion: it ended up taking place on my user talk-page. --JBL (talk) 17:09, 30 June 2023 (UTC)

An object that might deserve mention in this article

The extended weak order of Coxeter groups (general reference by Dyer: journal, arXiv) has, in the case of the affine symmetric group, a nice combinatorial representation (Barkley--Speyer: arXiv & Barkley: extended abstract) in terms of total orders on Z that obey $a\prec b$ if and only if $a+n\prec b+n$. (NB: there can be complicated order type, like $\cdots \prec -2\prec 0\prec 2\prec \cdots \prec 3\prec 1\prec -1\prec \cdots$ when $n=2$.) This extends the poset of regions of the affine braid arrangement (viewed as a linear hyperplane arrangement) to a lattice. It is conjectured (but not proved) that the extended weak order of any Coxeter group is a lattice. It might be worth adding something on this at some point, perhaps after more of these references are published. --JBL (talk) 17:28, 5 August 2024 (UTC)