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    There are some tags that strike me as duplicative. Namely:

    fourier-analysis fourier-transform
    monoidal-categories modular-tensor-categories
    derived-category derived-stuff
    categories category-theory
    graphs graph-theory
    homology homological
    publication publishing

    Should we try to merge them in some way?

    Good idea, and it sounds like this can be done now by moderators and also given as a job in the future to this user.

    By the way, to find out which ones to keep, here are some examples of retagging from Stack Overflow:

    Continuing the previous topic, I think we could now try to write the Tagging FAQ, to be shown to 250--500+ rep users (I think once is enough, as with regular FAQ, no need to nag them all the time). Shall there be some wiki?

    Update: a relevant discussion + explanation of tagging philosophy


    @David: I've made the following merges:

    Master Tag            Removed/Renamed Tag
    fourier-analysis      fourier-transform
    derived-category      derived-stuff
    category-theory       categories
    graph-theory          graphs
    publishing            publication

    I'd like to get some confirmation before I merge [monoidal-categories] and [modular-tensor-categories] because it looks like the people using those tags really mean for them to be different, and merging tags is irreversible. The tag [homological] appeared because somebody accidently used the two tags [homological] and [algebra] instead of [homological-algebra]. Should the [homology] and [cohomology] tags be merged into [homological-algebra]?

    @Ilya: Thanks for those links. Support for synonym tags would be great. I think this thread on meta.MO should serve the same purpose as the great tagging reorg. I'm not sure what you mean when you say that merging tags could be done by the Community user. I definitely don't want tags to be merged automatically; a person should make the decision. Perhaps what you meant is that when somebody tries to use the tag [graphs], it is automatically converted to [graph-theory], effectively making them synonyms.


    I'd be happy for homology and cohomology to be merged with each other but not with homological algebra. I would tend to skip past homological algebra questions but would avidly devour homology and cohomology ones.


    I guess ideally one would be able to define a hierarchy of tags so that [topology] "owned", say, [homotopy theory] and searching by a high level tag brought up all the lower ones as well. This would make sense outside mathematics - has anything like it been tried on the other SE sites?

    I don't think homology/cohomology is the same as homological-algebra. I would use homological-algebra for questions about the machinery of Ext, Tor, long exact sequences, spectral sequences, etcetera. I would use homology/cohomology for questions about the homology of topological spaces, coherent sheaves or some other specific field in which homological techniques were used. Of course, there is an overlap, but I don't think they are the same.
    I may be wrong about monoidal-categories versus modular-tensor-categories. Would any experts like to comment?
    • CommentAuthorrwbarton
    • CommentTimeNov 9th 2009

    A modular tensor category is indeed a monoidal category but one with approximately a zillion extra properties or pieces of structure. A typical example of a modular tensor category is the category of finite-dimensional representations of a finite group. A typical example of a monoidal category is a monoid viewed as a category with only identity morphisms. (I think you may have been confused by what is a pet peeve of mine, namely, people using "monoidal category" or "tensor category" when they really have a lot of extra structure in mind, such as enrichment in some abelian category. To a category theorist, such categories are the exception rather than the rule.)

    • CommentAuthorrwbarton
    • CommentTimeNov 9th 2009

    I mentioned this elsewhere, but how about merging supersymmetry and super-linear-algebra to super-stuff?

    I thought supersymmetry was some sort of physics thing that I don't understand. Super linear algebra is simply generalizing linear algebra to work with a funny twist in the R-matrix. I would avoid posts about supersymmetry and read posts about super linear algebra.
    • CommentAuthorrwbarton
    • CommentTimeNov 9th 2009 edited

    Right, I guess I should have added, if you look at the posts currently tagged supersymmetry, I'm sure you'll understand more than half of them, because they aren't really about supersymmetry, but super-stuff in general. (I guess the ones I don't understand might actually be about supersymmetry.)


    @Anton, re: community user

    what you meant is that when somebody tries to use the tag [graphs], it is automatically converted to [graph-theory]

    My idea was that Community User, a bot, can be given an automated task to continue to retag the questions that were right now retagged manually, but now I think synonym system would be better if people were told about them when posting.

    Here's the feature request in case somebody wants to look/upvote.


    @Ilya: But what would the bot actually do. How would it decide how to retag questions? That is, what manual retags are we doing now that could actually be done by a bot?


    What I meant is that the bot would continue with "fourier-transform" --> "fourier-analysis" and the other tags listed above. (I now think other solutions are more efficient for this issue)


    I understand now. I'll look into whether it's possible to do something like that. For now, I can just manually merge the tag [fourier-transform] into [fourier-analysis] whenever it gets to be a problem.

    By the way, you were one of the people saying we shouldn't load jsMath on the summary pages. Can you confirm that those pages are snappier to respond?


    Yes, they seem to be. I tried comparing 3 Shift-Reloads on summary pages and of questions with jsMath and the results are

    Summary: 4s 6s 6s
    Questions: 7s 9s 10s


    Should [jobs] be merged into [career]?


    I would say "jobs" sounds like actual job advertisements (which may be MO shouldn't have at all) while "career" for the general process of growing up in the profession, so, yes, merge the existing tags.


    modular-tensor-categories is pretty obscure, but it is a research interest of several users. certainly it's not even close to synonymous with monoidal category.


    I think job advertisements are definitely not appropriate. just putting that out there.


    Ok, I've merged [jobs] into [career].


    Should [odes] and [pdes] be merged into the more popular [differential-equations]?

    +1 [odes],[pdes] ---> [differential-equations]

    Yes, though probably someone will create them again.


    done. I have no problem playing custodian and merging [odes] and [pdes] into [differential-equations] every couple of months.

    Actually, I don't understand the [odes]+[pdes] merger at all. Here are two major areas of mathematics, big enough to have separate top-level codes in the MSC, lumped into just one tag, while much of the rest of the tag cloud seems pretty fine grained from my perspective. It makes no sens to me, unless it merely reflects the fact that there aren't a lot of differential equations people active at MO (yet). But I am not convinced that popularity should decide the granularity of the tagging system anyhow. Well, to a moderate degree perhaps, but this seems extreme. Actually, I find quite a number of tags which have apparently never been used at all, so popularity isn't an explanation. I don't know what it is, then.

    @hanche: Originally, I created the tags [odes] and [pdes], but people who talked about differential equations didn't use these tags. Instead, they created and used the tag [differential-equations]. The reason for merging was not unpopularity of the [odes] and [pdes] tags, it was the popularity of the [differential-equations] tag. If people who do differential equations start making finer distinctions in new tags they create, I'm happy to allow it.

    Incidently, Theo was recently working on convincing me that pdes are really the same thing as odes.


    @Anton: They are, but don't tell anyone because it's a secret.

    Seriously, they are if you allow infinite dimensions but Picard only works in finite dimensions so if you like the classification should be:

    ODE <-> DE+Picard
    PDE <-> DE-Picard

    More seriously (and back to the topic), I guess a reasonable policy would be to merge tags where they are used synonymously, rather than making it a statement about those fields of research, which seems to be your explanation for this case. As always, it is important to make the policy clear.

    • CommentAuthorKevin Lin
    • CommentTimeNov 13th 2009
    Generally people on this site (and elsewhere, like on the arxiv) tag stuff about complex manifolds with "algebraic geometry". Personally I would prefer to tag such questions with "complex geometry" or "complex manifolds", especially if the question is not necessarily about complex varieties. Are there any objections to this? Are there any preferences vis a vis "complex geometry" versus "complex manifolds"?

    [complex-geometry] already exists, but [complex-manifolds] does not.

    Should [complex-geometry] be merged into [cv.complex-variables]? Should [physics] be merged into [mp.mathematical-physics]?

    I like the idea of [physics] ---> [mp.mathematical-physics], mostly as it might encourage keeping people on topic. People might see there's no [physics] tag, just [mp.mathematical-physics], and reconsider their question. Or so we can hope!

    I'm considering creating a [remove-this-tag] tag for the purpose of merging unwanted tags into it. For example, today I realized that the [newbie] tag exists. I'd really like to delete it (so that new users can't use it), but there is no way to do that, and I can't really think of a way to make that a feature-request because it could leave some questions with no tags at all. Does anybody object to [remove-this-tag]?

    I want to get a mathematical physicists opinion on [physics]→[mp.mathematical-physics] before I do it. I'll try to find one today.

    +1 [remove-this-tag] but [please-retag] is probably even better -- it gives new users an easy way to request retagging when they can't do it themselves.

    But they already have lots of ways to request retags if they can't do it themselves: they can leave a comment on the post, or (since they are the author) they can just ask in the body of the post. I would be pretty surprised if a 500+ rep user didn't respond to such a request within an hour.

    I feel like [please-retag] indicates that there is a problem with the other tags (it sounds like that's actually what you had in mind), but [remove-this-tag] very clearly only refers to itself.

    • CommentAuthorKevin Lin
    • CommentTimeNov 13th 2009
    I also think merging [physics] with [mathematical-physics] is a good idea.

    I think [complex-geometry] should be distinct from [complex-variables], just as [differential-geometry] should be distinct from [analysis] or [real-analysis] or [calculus].

    @Scott: Does adding a tag require less rep than retagging? I haven't seen that mentioned anywhere. (More, I see no way that I can add a tag to an existing quiestion, and I have almost enough rep to retag by now.) If not, I fail to see your point. [remove-this-tag] seems good.

    But actually, I am very surprised not to see a feature that I thought would be an obvious one: When you enter a new question, there is no easy way to pick a tag from among the existing ones. You have to open the tags page and search it, then enter the name of the tag (correctly!) in the tags field. I think it ought to be harder to enter a new tag than to use an existing one.


    Oh, wait, re my latest complaint: I see now that it does suggest existing tags while you type, but only intermittently in my experiments. I have no idea what triggers the popup of possible tags. It seems highly random, and I had obviously not seen it yet when I first wrote on this.

    So, assumeing this actually works, maybe a tag [partial-differential-equations] would work okay? Users would see it when they start typing differential- in the box. If lucky. The arxiv-derived tag would be ap.analysis-of-pdes, but I doubt that many users are going to stumble across that one.


    @hanche: adding a tag requires the same 500 rep as retagging. The tag-suggestion feature should work all the time, but it might be slow for two reasons: (1) you're on a shaky internet connection, or (2) Fog Creek is getting a lot of traffic. Fog Creek has said that once SE is out of beta, the'll be doing much more optimizing for speed, so hopefully, that second possibility will eventually never come up.

    I agree that [ap.analysis-of-pdes] isn't so good because it doesn't utilize the tag-suggest feature. I vote for [ap.partial-differential-equations], but I don't have strong feelings.


    differential-geometry and dg.differential-geometry

    • CommentAuthorrwbarton
    • CommentTimeNov 16th 2009

    I see there are a bunch of questions labeled sg-symplectic-geometry. I assume it should be sg.symplectic-geometry.


    von-neumann-algebras and c-star-algebras could be merged into oa.operator-algebras, I think. This might need to be redone from time to time.


    Did [differential-goemetry]-->[dg.differential-geometry] and [sg-symplectic-geometry]-->[sg.symplectic-geometry]. Could somebody confirm or deny hanche's suggestion of [von-neumann-algebras], [c-star-algebras] --> [oa.operator-algebras]? My understanding is that [oa.operator-algebras] is a strictly broader tag, in the same way that [ag.algebraic-geometry] is strictly broader than [moduli-spaces], which would suggest that we should keep the more specific tags, but I don't know anything about operator algebras.


    We should definitely keep von-neumann-algebras and c-star-algebras as more specific tags.


    You're right that [oa.operator-algebras] is strictly broader than [von-neumann-algebras] and [c-star-algebras]. I guess I am still confused about policy after being puzzled about the [differential-equations] thing. But then, at least, everything that's tagged either [von-neumann-algebras] or [c-star-algebras] should be tagged [oa.operator-algebras] as well, right?

    1. i'd like to keep von-neumann-algebras and c-star-algebras as tags as well. i'm going to retag my questions for which these have been removed, but i will still keep oa.operator-algebras.

    2. i created the tag qa.quantum-algebra. can we merge quantum-algebra into this tag?

    just did [quantum-algebra]-->[qa.quantum-algebra].

    @hanche: I think the tags [odes] and [pdes] were a fine idea (I created them, after all), but people just weren't using them. Tagging is something that the community has to develop a standard for. Of course, we can influence tagging conventions a great deal, but ultimately the smartest thing to do is to look at how most people are actually using the tags, and merge/rename in such a way that it becomes easier for everybody else to follow the de facto conventions. I'm certainly not absolutely sure that merging [odes],[pdes] in to [differential-equations] was the right thing to do. If [odes] and [pdes] get recreated and people start using them meaningfully, I have no intention of interfering.


    I'm merging [point-set-topology] into [gn.general-topology] as requested here. There are a handful of [point-set-topology] questions that aren't tagged [gn.general-topology], but I want to retag them [gn.general-topology] (all but one of them have no arXiv tag).

    • CommentAuthorJonas Meyer
    • CommentTimeJan 6th 2010 edited
    I don't think you created it, unless something else just got merged. There are 13 other questions with that tag.

    Edit: This was in reply to someone who later abruptly deleted many of his posts. It seems we can no longer delete our posts here, but if a moderator would like to remove this one, feel free.

    [spectral-theory] → [sp.spectral-theory], please?


    @hanche: done.