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  1. Add a reference for string diagrams in closed monoidal categories


    diff, v42, current

    • CommentRowNumber2.
    • CommentAuthora_delpeuch
    • CommentTimeJul 28th 2019
    Wow, there is not a single string diagram shown on the page "string diagram".
    How can this page be useful to anyone who does not already know about these diagrams?
    Surely it cannot be accidental - am I missing something here? I guess I will try to add some myself and see what happens…
    • CommentRowNumber3.
    • CommentAuthorMike Shulman
    • CommentTimeJul 28th 2019

    I expect this is because it’s only very recently that functionality like tikz was available on the nlab for drawing string diagrams. Before that they would have had to be included images or svg, and probably no one wanted to put in the effort.

    • CommentRowNumber4.
    • CommentAuthorDavid_Corfield
    • CommentTimeJul 29th 2019
    • (edited Jul 29th 2019)

    Wow, why is someone surprised that a wiki constructed by a very few guys in their spare time doesn’t have every desirable feature?

    The only “accidental” thing is that there are so few people who can be bothered to contribute.

    • CommentRowNumber5.
    • CommentAuthora_delpeuch
    • CommentTimeJul 31st 2019
    • (edited Jul 31st 2019)
    Sorry, I did not mean to offend the previous contributors… but for me it is a bit symptomatic of the overall style of the house.

    If my additions of diagrams are welcome then I will keep doing that. I just wanted to double check that I had not missed some reason why diagrams had been left out.
    • CommentRowNumber6.
    • CommentAuthorDavid_Corfield
    • CommentTimeJul 31st 2019

    No, there is no reason that diagrams have been left out. It’s just a question of the changing interests and energy levels of the very few people here, and the functionality available.

    I can’t imagine what you took a lack of string diagrams to be a symptom of. Mike Shulman has publications using them, such as Traces in symmetric monoidal categories. So do I for that matter, Ch. 10 of my book.

    I see you added one at double category. Keep it up. Plenty of opportunities obviously on this page, string diagram.

    • CommentRowNumber7.
    • CommentAuthorTodd_Trimble
    • CommentTimeJul 31st 2019

    “Style of the house.” Sigh.

    There is no house style. Each contributor has his/her own style of writing. (There are a few conventions, but they do not dictate style.)

    • CommentRowNumber8.
    • CommentAuthorMike Shulman
    • CommentTimeJul 31st 2019

    I don’t think we should be surprised that people think there is a “house style”, or that decisions about what or what not to include were made in some centralized or intentional way, or that by adding something to scratch their own itch they might be violating some norms or expectations. The idea of a truly decentralized wiki is still alien to the way people are used to thinking about the way things are written and created. Most people’s experience with wikis is limited to wikipedia, which is nowadays much more centralized and controlled than we are, and probably looks even more so than it is to the casual reader.

    (I’m not necessarily claiming that any of this applies to any particular person such as a_delpeuch, just responding to the general feeling of frustration with this misconception that David and Todd are expressing — which I do share, but I’m more or less resigned to it by now.)

    • CommentRowNumber9.
    • CommentAuthorDavid_Corfield
    • CommentTimeJul 31st 2019
    • (edited Jul 31st 2019)

    Some of my annoyance is a carry-over from reading some ill-informed comments on Twitter. Some people seem to think that unless an entry is swimming in (,1)(\infty, 1)-tags that we don’t want to know. No doubt it would be better for me not to read this, but it has made me aware that there are people under the banner of ’Applied Category Theory’ who have the impression that it will require a radical shift to have their ideas represented here.

    While some scepticism was expressed about the ACT-movement in the corresponding discussion, the one explicitly anti-ACT view aired on the nForum that I know about was given anonymously by ’Guest’ at game theory.

    Ah, now I see that a_delpeuch participated in the discussion Applied Category Theory on the nLab. The idea that we’re ultra-abstract and unapplied is in the air.

    Can’t people just come along with a modicum of humility, find out a little bit about how things work around here, and then get on with providing some content?

    • CommentRowNumber10.
    • CommentAuthorTodd_Trimble
    • CommentTimeJul 31st 2019

    I’m tempted to start writing “Myths About the nLab”, but I’ll hold off on that.

    IIRC, Urs said something in the other thread (linked to by David C in the last comment) about not letting all these meta-thoughts about the nLab get in the way. I agree. There’s a lot to be done, so if you have something useful you’d like to add, please just go ahead. Personally, I’m really glad that a_delpeuch is putting in string diagrams. We need them, and needed them. The lack had nothing to do with any supposed philosophical or stylistic opposition to them.

    • CommentRowNumber11.
    • CommentAuthorDavid_Corfield
    • CommentTimeAug 1st 2019

    All very odd when you consider that of the authors of the last three comments, two have done important mathematical/logical work with string diagrams and the other has discussed their philosophical importance.

  2. Added links to PDF files of 1965 habilitation thesis of G. Hotz

    Armin Reichert

    diff, v49, current

    • CommentRowNumber13.
    • CommentAuthorTodd_Trimble
    • CommentTimeNov 15th 2019

    Re #12: very interesting! I’ve only just taken a quick glance, because German is a significant obstacle for me in reading mathematics, but why is this history not better known?

    • CommentRowNumber14.
    • CommentAuthorMike Shulman
    • CommentTimeNov 15th 2019

    Perhaps that question contains its own answer? (-:O

  3. Added a link to Petri net in the related concept section.

    Jade Master

    diff, v51, current

    • CommentRowNumber16.
    • CommentAuthorUrs
    • CommentTimeDec 6th 2019

    added pointer to

    in the process, I have merged the References-subsection that used to be separate as “Introductions” and “Surveys”.

    diff, v52, current

    • CommentRowNumber17.
    • CommentAuthorUrs
    • CommentTimeDec 6th 2019

    There is an old query box in the entry, essentially challenging the truth of the assertion that Kelly-Laplaza’s articles speaks about string diagrams at all:

    Where in Kelly-Laplaza do string diagrams appear? I can’t find any picture of a string diagram in the paper. Perhaps they are described somewhere in the text, but I can’t see it.

    This should be easy to settle…

    diff, v52, current

    • CommentRowNumber18.
    • CommentAuthorTodd_Trimble
    • CommentTimeDec 6th 2019

    Although it seems the revision where the claim first appears was made by Urs, I might have had something to do with the spread of such a rumor. Anyway, if someone looked and didn’t see it, I’m sure the claim is false. I don’t have the article to hand.

    • CommentRowNumber19.
    • CommentAuthorUrs
    • CommentTimeDec 7th 2019
    • (edited Dec 7th 2019)

    Thanks for checking. I don’t remember having made that edit, but apparently then I have. Certainly I never looked at that book.

    So now I did a search for “history of string diagrams” and found this helpful message by Pawel Sobocinski, where it seems to clarify what’s going on:

    Many calculations in earlier works were quite clearly worked out with string diagrams, then painstakingly copied into equations. Sometimes, clearly graphical structures were described in some detail without actually being drawn: e.g. the construction of free compact closed categories in Kelly and Laplazas 1980 “Coherence for compact closed categories”.

    Will edit the entry accordingly…

    • CommentRowNumber20.
    • CommentAuthorUrs
    • CommentTimeDec 7th 2019

    so I added a bunch of references, and missing publication data for previously existing references, to the section References – Original articles.

    Now is starts out as follows (there was and is overlap with the subsequent section References – Details, which I have not tried to deal with):

    The development and use of string diagram calculus pre-dates its graphical appearance in print, due to the difficulty of printing non-text elements at the time.

    Many calculations in earlier works were quite clearly worked out with string diagrams, then painstakingly copied into equations. Sometimes, clearly graphical structures were described in some detail without actually being drawn: e.g. the construction of free compact closed categories in Kelly and Laplazas 1980 “Coherence for compact closed categories”.

    (Pawel Sobocinski, 2 May 2017)

    This idea that string diagrams are, due to technical issues, only useful for private calculation, is said explicitly by Penrose. Penrose and Rindler’s book “Spinors and Spacetime” (CUP 1984) has an 11-page appendix full of all sorts of beautiful, carefully hand-drawn graphical notation for tensors and various operations on them (e.g. anti-symmetrization and covariant derivative). On the second page, he says the following:

    “The notation has been found very useful in practice as it grealy simplifies the appearance of complicated tensor or spinor equations, the various interrelations expressed being discernable at a glance. Unfortunately the notation seems to be of value mainly for private calculations because it cannot be printed in the normal way.”

    (Alex Kissinger, 2 May 2017)

    The first formal definition of string diagrams in the literature appears to be in

    • Günter Hotz, Eine Algebraisierung des Syntheseproblems von Schaltkreisen, EIK, Bd. 1, (185-205), Bd, 2, (209-231) 1965 (part I, part II)

    Application of string diagrams to tensor-calculus in mathematical physics (hence for the case that the ambient monoidal category is that of finite dimensional vector spaces equipped with the tensor product of vector spaces) was propagated by Roger Penrose, whence physicists know string diagrams as Penrose notation for tensor calculus:

    See also

    From the point of view of monoidal category theory, string diagrams are first described (without actually being depicted, see the above comments) in


    and in

    String diagram calculus was apparently popularized by its use in

    Probably David Yetter was the first (at least in public) to write string diagrams with “coupons” (a term used by Nicolai Reshitikhin and Turaev a few months later) to represent maps which are not inherent in the (braided or symmetric compact closed) monoidal structure.

    If anyone has a reference that would go with “Probably David Yetter was the first…” that would be good to add.

    diff, v54, current

    • CommentRowNumber21.
    • CommentAuthorDavid_Corfield
    • CommentTimeDec 7th 2019

    Something I’ve been meaning to ask with Urs drawing these diagrams of late is where Cvitanovic’s bird tracks fit inside the family of diagrammatic notation.

    • CommentRowNumber22.
    • CommentAuthorUrs
    • CommentTimeDec 7th 2019

    Might you have a more specific link? I have been looking around there for a bit, but still haven’t seen any discussion of “bird tracks”.

    • CommentRowNumber23.
    • CommentAuthorUrs
    • CommentTimeDec 7th 2019

    added publication data and links for this one:

    diff, v55, current

    • CommentRowNumber24.
    • CommentAuthorUrs
    • CommentTimeDec 7th 2019
    • (edited Dec 7th 2019)

    Okay, I found those birdtracks:

    one needs to

    1) go to

    2) then choose “webbook” from the menu on the left,

    3) then click on the words “hyperlinked pdf” (which is not self-evident, as it’s not underlined)

    4) then (one does not get a pdf but) one has to wait for the web display to load…

    5) then finally scroll forward to page 8.

    There is an “Example” which is actually where the “birdtracks” seem to be defined, and, at least on this and the following pages, they are just the standard Penrose/string diagram notation for tensor calculus in (FinVect,)(FinVect, \otimes).

    This should be added to the entry on string diagrams. But I won’t do it.

    • CommentRowNumber25.
    • CommentAuthorUrs
    • CommentTimeDec 7th 2019

    added publication data for this reference:

    diff, v56, current

    • CommentRowNumber26.
    • CommentAuthorUrs
    • CommentTimeDec 7th 2019
    • (edited Dec 7th 2019)

    started an Examples-section (here)

    For the moment it contains nothing but pointers to entries on Lie theory that show some string diagrammatics.

    But if any entry deserves a good supply of graphical examples, it is this one here, and so maybe a stub entry named “Examples” reminds/motivates someone to add such.

    diff, v57, current

    • CommentRowNumber27.
    • CommentAuthorUrs
    • CommentTimeDec 24th 2019

    added these pointers:

    diff, v58, current

    • CommentRowNumber28.
    • CommentAuthorUrs
    • CommentTimeJan 6th 2020
    • (edited Jan 6th 2020)

    added pointer to

    diff, v59, current

    • CommentRowNumber29.
    • CommentAuthorUrs
    • CommentTimeJan 8th 2020

    added to the list of examples (here) a pointer to ’t Hooft double line notation

    diff, v60, current

  4. Broken link fixed.

    Matteo Durante

    diff, v61, current

  5. Added

    • George Kaye, The Graphical Language of Symmetric Traced Monoidal Categories, (arXiv:2010.06319)

    diff, v65, current

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