Wikipedia talk:WikiProject Mathematics/Archive/2019/Jun

Nail H. Ibragimov

A new article on mathematician Nail H. Ibragimov has been nominated for deletion. Feel free to weigh in with your opinions at the AfD, but I have a different request. In the current version of the article, at the bottom in the "Further reading" section, there is a link to a three-page biography of Ibragimov, in Russian, published for his 70th birthday. I think it would be useful in expanding the text of our article, but I don't read Russian and (as an image of a printed document rather than web text) it's inconvenient to run through an automatic translator. Would someone who does read Russian like to give it a try? —David Eppstein (talk) 20:59, 1 June 2019 (UTC)

You may be able to run the images of Russian text through OCR software, either locally or online. I tried onlineocr.net which normally works well but it failed to give any useful results from these images. Certes (talk) 22:01, 1 June 2019 (UTC)

Update: the images are PNG, which onlineocr.net doesn't handle. Converting them to JPG then putting them through onlineocr.net produces Russian text almost ready for automatic translation, though it could do with being cleaned up by a Russian speaker first. Other OCR tools may handle PNG directly. Certes (talk) 22:26, 1 June 2019 (UTC)

If so, please make the text (in Russian or English) available (on that talk page, or otherwise); then I should be able to clean it up. Though, it is 3 pages long. What really do we want there? By the way, the corresponding article in Russian wikipedia is short. Boris Tsirelson (talk) 22:29, 1 June 2019 (UTC)

Something about his career after he finished his Dr.sci. might be helpful. E.g. how did he end up in South Africa and why did he move from there to Sweden? Also, is Rustem Khamitov his step-son? —David Eppstein (talk) 22:46, 1 June 2019 (UTC)

I see.

Wow, no need in OCR! The PDF file is available for download on the same cite; I just copied its text to our talk page. Boris Tsirelson (talk) 04:13, 2 June 2019 (UTC) English translation added. But I am not guilty if David's questions remain unanswered.   :-)   Boris Tsirelson (talk) 05:54, 2 June 2019 (UTC)

Nomination of Portal:Geometry for deletion

A discussion is taking place as to whether Portal:Geometry is suitable for inclusion in Wikipedia according to Wikipedia's policies and guidelines or whether it should be deleted.

The page will be discussed at Wikipedia:Miscellany for deletion/Portal:Geometry until a consensus is reached, and anyone is welcome to contribute to the discussion. The nomination will explain the policies and guidelines which are of concern. The discussion focuses on high-quality evidence and our policies and guidelines.

Users may edit the page during the discussion, including to improve the page to address concerns raised in the discussion. However, do not remove the deletion notice from the top of the page. North America¹⁰⁰⁰ 23:25, 2 June 2019 (UTC)

Covering lemma and Core model

Should the article covering lemma and core model be merged? Neither has enough context that I can be sure I understand them, and both seem to make little sense without the other. I am a set theory expert, but am not good with large cardinals.... — Arthur Rubin (talk) 16:45, 3 June 2019 (UTC)

No, I don't think they should be merged. The core model K, as I understand it, is a slightly imprecisely defined term in the most general case. It becomes well-defined when you have some smallness assumption on the universe. For example, if 0# does not exist, then the core model is just L. If there is no measurable cardinal, then the core model is the original Dodd–Jensen core model, obtained by starting with L[U] and iterating the measurable up out of the top of the universe. And on and on, adding a smallness assumption that says large cardinals just beyond the ones you're studying don't exist.

With no smallness assumption, I've never managed to get the folks who understand this stuff to completely nail themselves down on whether the notion is precisely defined, but they throw around terms like "the union of all L[E] models where E is an extender sequence".

In any case, the core model is a notion of an inner model that fills out everything you can fill out just by adding large cardinals.

The covering lemma, on the other hand, is a flexible name for a theorem, which is quite a different thing from a flexible name for a model. The original covering lemma is the one that applies to L if 0# does not exist. I don't think you would want to merge that with the article on L, would you? So merging the general name with the general article on K doesn't seem to make sense either. --Trovatore (talk) 20:00, 3 June 2019 (UTC)

Math community group

Anyone interested in an international math community group https://meta.wikimedia.org/wiki/Wikimedia_Community_User_Group_Math ? --Physikerwelt (talk) 21:41, 4 June 2019 (UTC)

A proposal for WikiJournals to become a new sister project

Over the last few years, the WikiJournal User Group has been building and testing a set of peer reviewed academic journals on a mediawiki platform. The main types of articles are:

• Existing Wikipedia articles submitted for external review and feedback (example)
• From-scratch articles that, after review, are imported to Wikipedia (example)
• Original research articles that are not imported to Wikipedia (example)

Proposal: WikiJournals as a new sister project

From a Wikipedian point of view, this is a complementary system to Featured article review, but bridging the gap with external experts, implementing established scholarly practices, and generating citable, doi-linked publications.

Please take a look and support/oppose/comment! T.Shafee(Evo&Evo)^talk 11:09, 5 June 2019 (UTC)

For us mathematicians, two mathematical examples (out of two existing, do not blame me for the choice): Spaces in mathematics (external review and feedback); Can each number be specified by a finite text? (explanatory essay, submitted, not to be imported to Wikipedia). Boris Tsirelson (talk) 17:34, 5 June 2019 (UTC)

English versus European terminology

Several years ago there was a lengthy argument between myself (under my old username "SharkD") and another user (User:Ag2gaeh) over the usage of terminology related to 3D projection and descriptive geometry, especially the terms "Axonometry" and "Axonometric projection". However there seems to be a difference in English sources versus European sources. For instance, I did two brief surveys of English language sources (#1, #2), but the European literature seems to differ in many ways. I was wondering if someone could take a look into the topic. There also seems to be a language issue, in that the original author of Axonometry is not fluent in English, so I'm not clear exactly on how the literature differs, except that "axonometry" in Europe seems to include all types of parallel projection, not just a few types as is common (but not universal) in English sources. In general I am wondering if we should switch over to the European terminology. ➧datumizer  ☎  09:32, 29 May 2019 (UTC)

Some specific questions:

• Are parallel projection and axonometry/axonometric projection synonymous?
• Do the terms isometric, dimetric and trimetric apply equally to oblique projections?
• Do the terms orthographic and orthogonal refer to the angle between the viewing direction and the projection plane, or to the angle between the principal faces of an object (for instance a cube) and the projection plane?

Thanks. ➧datumizer  ☎  09:58, 29 May 2019 (UTC)

@Datumizer: A minor note about 'steps' order dependency' in Axonometry#Principle of axonometry: the clause refers to three bulleted sub-steps inside the step 3, not to steps 1 through 4 – started from zero-zero you can go by x in the X direction, then by y in the Y direction or the other way, and you'll get to the same (x, y) point. Similarly you can make the Z step before, between or after X & Y steps and finally get to the same (x, y, z). --CiaPan (talk) 10:29, 29 May 2019 (UTC)

I have renamed sub-steps. :) CiaPan (talk) 10:34, 29 May 2019 (UTC)

As far as I know, the terms "axonometry" and "axonometric" are no more in use in mathematics, except for describing applications to graphics. Presently these are terms specific to graphical representation, typically in architecture and industrial design. So, for the most usual meanings to the terms, you must consider sources in specialized areas. In mathematics, the reliable (for this question) sources that you can find are probably more 100 years old, and thus not reliable for a modern encyclopedia.

About your first specific question: Translated in modern mathematics language, Axonometry#Principle of axonometry defines axonometry as an affine mapping of the 3D-space onto a plane. Pohlke's theorem means that these affine mappings are the composition of a parallel projection and a similarity (this is explicitly said on this article. This answers your first question, by no. Similarity must not be forgiven, as the graphical representation of a building cannot be the result of a parallel projection (at least because of the respective sized of the building and the paper sheet). — Preceding unsigned comment added by D.Lazard (talk • contribs) 12:01, 29 May 2019 (UTC)

So, are you saying that parallel projections can include representations of objects that are dissimilar? Or, that parallel projections are never scaled up or down and are always 1:1 representations of objects? Which is greater in scope? ➧datumizer  ☎  03:20, 30 May 2019 (UTC)

A parallel projection of a sphere is a circle of the same radius. As buildings contain generally sphere of large radius, a parallel projection of a building cannot fit in a paper sheet without being scaled, and scaling is a similarity. In summary, Pohlke's theorem asserts that "axonometry", "affine map from 3D to 2D", and "composition of a parallel projection and a similarity" are three synonyms. On the other hand two non-similar plane figures may have the same image by axonometry: clearly a plane figure and its image by a parallel projection have the same image by the same parallel projection; they are similar if and only if the plane of the figure is perpendicular to the direction of projection in general, they are not similar if the planes of the figure and its image are not parallel. D.Lazard (talk) 09:35, 30 May 2019 (UTC)

@D.Lazard: Is it assumed the projecting rays are perpendicular to the projection plane? Because if they needn't, then your last sentence is false: an arbitrary planar figure will be similar (actually: congruent) to its parallel projection if (but not only if, in special cases) the figure plane is parallel to the projection plane, for arbitrary projection direction (not parallel to the plane, of course). --CiaPan (talk) 09:46, 30 May 2019 (UTC)

You are right, I have been too fast by writing my post. I have corrected it. About the "only if": It is clear that the projection of a line is always similar to it. I guess (I have not checked the details) that "if and only if" is true for bounded plane figures that are not contained in a line. D.Lazard (talk) 10:27, 30 May 2019 (UTC)

If you look at the illustrations in Axonometry, the three projected coordinate axes may generally go in any direction, and be scaled (foreshortened) to any length. This is not possible if the two planes must always be parallel. (In fact, there is a name for when the planes are not parallel: Oblique projection, a sub-class of axonometric projection according to European literature.) ➧datumizer  ☎  06:38, 1 June 2019 (UTC)

Anyway, it seems parallel projection amounts to a specific case of axonometric projection (if we agree that coincidence is a type of similarity), and that the latter has greater scope than the former. That clears things up for me, thanks. However, if we look at my survey of English sources (#1, #2) there is little agreement with this taxonomy. And this is also the case currently with English Wikipedia. What should we do? Should we just ignore the problem? ➧datumizer  ☎  06:46, 1 June 2019 (UTC)

• Parallel projection is defined without coordinate axes and coordinates. It includes orthogonal (normal) and oblique projections.

In German textbooks

• Axonometrie is a centuries old procedure generating a picture of a 3D-object using coordinate axes and coordinates. The latter are usually given implicitely by a pair of "zugeordnete Risse" ("Grundriss, Aufriss", which are connected orthogonal projections). The result of the axonometric procedure is a parallel projection + a uniform scaling (Pohlke's theorem). The so generated parallel projection is oblique or orthogonal. If one wants to generate an orthogonal projection, only the images of the coordinate axes can be prescribed (and not the foreshortenings !) , see the German article on orthogonale Axonometrie)

In English textbooks an axonometric projection seems to be always an orthographic (orthogonal)) projection.

• Mehrtafelprojektion (multiview projection ?) means 3 or more "zugeordnete Risse" ("Grundriss, Aufriss, Kreuzriss, ..."). If one deals with "Grundriss" and a connected "Aufriss" one calls it "Zweitafelprojektion". --Ag2gaeh (talk) 08:08, 1 June 2019 (UTC)

Addendum: An essential practical improvement of the procedure Axonometrie is the "Einschneideverfahren" (or "Schnellriss"), which is due to the Austrian mathematican Ludwig Eckhart. It omits determining single coordinates and their foreshortenings and facilitates marking image points.--Ag2gaeh (talk) 14:16, 1 June 2019 (UTC)

So, how should we proceed from here? ➧datumizer  ☎  21:04, 6 June 2019 (UTC)

It seems to me (see list of Your excerpts, above), that there are no clear definitions on axonometry in English literature. As I have no English text books to check and compare terms, I refrain from further editing on this subject.--Ag2gaeh (talk) 11:20, 7 June 2019 (UTC)

Wikipedia:WPM listed at Redirects for discussion

An editor has asked for a discussion to address the redirect Wikipedia:WPM. Please participate in the redirect discussion if you wish to do so. Steel1943 (talk) 15:37, 13 June 2019 (UTC)

Formulas in captions

I've started a discussion at WT:Manual of Style/Captions#Formulas in captions that may be of interest to folks here. –Deacon Vorbis (carbon • videos) 01:58, 17 June 2019 (UTC)

On a certain bug in our not-actually-LaTeX software

I found this in the article titled Random variable:

$\mathrm {ess} \sup _{\omega }|X(\omega )-Y(\omega )|$

It was coded like this:

\mathrm{ess } \sup_\omega|X(\omega)-Y(\omega)|

$\mathrm {ess} \sup _{\omega }|X(\omega )-Y(\omega )|$

I changed the code to this:

\operatorname{ess} \sup_\omega|X(\omega)-Y(\omega)|

But ideally, one would like to see this:

\operatorname*{ess sup}_\omega|X(\omega)-Y(\omega)|

This works in LaTeX, but it doesn't work here, in this software that people sometimes incorrectly call "LaTeX":

$\operatorname {*} {esssup}_{\omega }|X(\omega )-Y(\omega )|$

That same code, in genuine LaTeX, would yield something about like this:

${\underset {\omega }{\operatorname {ess} \sup }}|X(\omega )-Y(\omega )|$

But here we have to code that as follows:

\underset \omega {\operatorname{ess} \sup} |X(\omega)-Y(\omega)|

I don't like doing that in lots of Wikipedia articles because some day this bug may be fixed and in fact people do learn how to code these things by looking at code that they find here.

I think this has been reported (I seem to recall having reported it a couple of years ago), and that means some time before the 29th century developers may get to it, or may not. Can anything be done to get this attended to besides hoping that developers who don't understand the need understand the need? Michael Hardy (talk) 21:14, 15 June 2019 (UTC)

I've noted this, and probably reported it as well, but kind of lost hope with respect to math rendering stuff getting improved, or even fixed. –Deacon Vorbis (carbon • videos) 01:57, 17 June 2019 (UTC)

I think this is T185552. There are some workarounds on the bug page.

The long term solution is to remove the texvc system completely, but this is a complex task. There has been progress towards this via T195861. We have now sanitized the syntax removing all deprecate syntax on almost all wikis. This allows texvc to be removed without breaking anything. --Salix alba (talk): 06:45, 17 June 2019 (UTC)

@Michael Hardy: You can achieve this:

$\operatorname {\underset {\omega }{ess\ sup}} |X(\omega )-Y(\omega )|$

with:

\operatorname{\underset \omega {ess\ sup}} |X(\omega)-Y(\omega)|

(based on a workaround description Help:Displaying a formula#Starred operatorname \operatorname*). --CiaPan (talk) 10:29, 17 June 2019 (UTC)

≘

The redirect ≘ (U+2258 CORRESPONDS TO) which currently targets Binary relation has been nominated for deletion at Wikipedia:Redirects for discussion/Log/2019 June 18#≘, your comments in that discussion would be appreciated. Thryduulf (talk) 17:11, 18 June 2019 (UTC)

Mathematical formalism

Please can someone review the few remaining links to dab Mathematical formalism and divert them to relevant articles or unlink? Thanks, Certes (talk) 15:11, 17 June 2019 (UTC)

• Domain of discourse: done. Boris Tsirelson (talk) 16:09, 17 June 2019 (UTC)
• Informal mathematics: done. Boris Tsirelson (talk) 16:15, 17 June 2019 (UTC)

Thanks! We have a similar problem with Correspondence (mathematics), which discusses specific types of correspondence and has now been tagged as a dab. Certes (talk) 15:42, 18 June 2019 (UTC)

I have edited Correspondence (mathematics) for using the standard style of dab pages. By the way, I have added 1:1 correspondence, and linked the entries that were tagged.

I have also disambiguated some links; a few by unlinking, when they refer to the common English meaning; those that appeared in a "See also" section, by removing the entry; the remainder ones by linking either to multi-valued function or to correspondence (algebraic geometry). Hoping that this summary can help those who will continue to dab the incoming links. D.Lazard (talk) 18:02, 18 June 2019 (UTC)

Thank you. We're now down to about a dozen links. I have boldly merged the incomplete disambiguation into Correspondence per WP:PARTIALDAB, and created a new redirect for the von Neumann meaning. Certes (talk) 18:57, 18 June 2019 (UTC)

Gap-Hamming problem

There is a new page titled Gap-Hamming problem. On the theory that "gap" is being used here as a common noun, I set the initial in lower case. If it's actually someone's name, then the article should say who that is and the hyphen in "gap-Hamming" should become an en-dash. I found no links to this article at all and added one to the "See also" section of Hamming distance.

So further work is needed. Michael Hardy (talk) 16:30, 24 June 2019 (UTC)

Sadly the original paper mentions neither gap nor Hamming. The other references are split between Gap and gap, often mixing them in the same paper, so I doubt that we are dealing with a Dr. Gap here. My first thought was that it might mean the "gap" between the strings, a vague and colloquial synonym for Hamming distance, but that would be tautologous, so I think it must refer to the communication gap which limits how much information Alice can share with Bob. I think we need a hyphen or even a space: "gap Hamming problem", i.e. the problem of estimating the Hamming distance over a gap, as used here and here. (That article can link in once we confirm the title.) Certes (talk) 17:19, 24 June 2019 (UTC)

That is entirely fair. The reference is not to a given name, but rather to the fact that there is an "allowable gap" in distance (of size roughly ${\sqrt {n}}$) where the answer can be indeterminate. So, the correct spelling should, indeed, be "gap-Hamming" following most English conventions, but as proper nouns are capitalized (and "Gap-Hamming" appears to have become its own term for an important problem in the field), I opted for capitalizing the G. I also added the dash (not an en-dash) as it appears to be customary in the field, but I agree with Certes that a space is likely the best possibility (though it is not standard when naming the problem in most papers).

Additionally, apologies, I'm not quite sure how to "properly" edit a talk page, so this might not be quite right :) Guilleunofficial (talk) 18:28, 24 June 2019 (UTC)

Zero divisors

Our article on Zero divisors may have some WP:NPOV problems, taking Bourbaki's choice to include 0 as a zero divisor as the "right" one, and being dismissive of those references that exclude it. In fact, in the four textbooks I checked (Gallian, Fraleigh, Rotman, and Dummit & Foote), every one of them excluded 0 in their definitions of zero divisors. I'm not sure of the best way to proceed, so I'll just leave this here, and anyone interested can take a whack at it. –Deacon Vorbis (carbon • videos) 17:36, 26 June 2019 (UTC)

Any ring element—0 included—is a divisor of itself, albeit a trivial divisor. Deacon Vorbis makes a project-wide problem off a linguistic nonce. Incnis Mrsi (talk) 18:19, 26 June 2019 (UTC)

The problem is that our article takes a WP:POV through its tone and its favoring of one source over others. This is not a problem that I created, but one that has existed at this article for some time. I posted here in order to seek assistance from other editors. If you have nothing constructive to offer, then please just keep it to yourself. –Deacon Vorbis (carbon • videos) 18:58, 26 June 2019 (UTC)

In Divisor#Definition, zero is not a zero divisor. On the other hand, in Regular sequence#Definition, zero is not a non-zero-divisor (and it is thus a zero divisor). D.Lazard (talk) 19:12, 26 June 2019 (UTC)