Wikipedia talk:WikiProject Mathematics/Archive/2013/Sep

"Current activities" page!
For those who may not be aware of it, this WikiProject has a "current activities" page, which lists new articles of interest to the project, articles for which deletion is proposed, articles needing further work, and various other things.

It is the creation of Jitse Niesen, who is thereby our benefactor.

It was down for about a week recently, and now it's back up. Michael Hardy (talk) 05:32, 31 August 2013 (UTC)
 * The old version of the bot seems to be fighting with the new toolserver version for control of this page. Whenever the old version updates, it takes things back to its down-for-a-week state. —David Eppstein (talk) 02:42, 1 September 2013 (UTC)

New content at metric (general relativity) and Riemann curvature tensor
New content at metric (general relativity) and Riemann curvature tensor is a bit rough, and needs copyediting (and probably a bit more than that). Sławomir Biały (talk) 21:48, 31 August 2013 (UTC)


 * I reverted both of those new sections by before I saw this comment. His work seems to be rather sloppy original research. JRSpriggs (talk) 11:58, 1 September 2013 (UTC)

AMS Fellows
In 2012 the AMS started a fellows program, to honor their members, and I've just finished populating the corresponding category, Category:Fellows of the American Mathematical Society, with our articles on people who are now fellows. There are nearly 600 people who are also fellows, but don't have articles; I've listed them at Category talk:Fellows of the American Mathematical Society. If you're looking for subjects for new Wikipedia articles, I think all of these would be suitable. —David Eppstein (talk) 23:57, 2 September 2013 (UTC)


 * Browsing that list, there are quite a few names that I'm surprised do not already have articles about them. I'll start a few stubs if I have time in the next few days.   Sławomir Biały  (talk) 12:03, 3 September 2013 (UTC)

Aleph_infinity
I am getting tired of reverting this "editor". Do we semiprotect Aleph number (and associated articles), or block 68.65.164.00/22? — Arthur Rubin (talk) 04:02, 4 September 2013 (UTC)
 * Looks like too much collateral damage. I guess semiprotection is the way to go.  — Arthur Rubin  (talk) 04:09, 4 September 2013 (UTC)
 * I've semiprotected that one (for a year, given that this has been happening for months). Do let me know if there are other articles that need the same treatment. —David Eppstein (talk) 05:01, 4 September 2013 (UTC)

Dendroid (topology) up for deletion
Hello WikiProject Mathematics people.

I've declined the speedy and turned it into a WP:PROD. For perhaps not so obvious reasons I don't really know where to go with this article, so I'll leave it with y'all.

Pete "really struggled to pass high school maths" in Australia aka --Shirt58 (talk) 10:25, 3 September 2013 (UTC)


 * It's not really a prod candidate either. There are quite a few references on Google scholar.  The term seems to go back to this paper from 1961 (where it is credited to a seminar given by Knaster at Uniwersytet Wrocławski), although they appear to have been studied in the 1950s by Karol Borsuk and others.  I'll add the 1961 reference to the article.   Sławomir Biały  (talk) 11:46, 3 September 2013 (UTC)
 * This, Dendrite (mathematics), Unicoherent space are stubs on closely related subjects. To me it would be better to have a single article covering all three as well as hereditarily unicoherent spaces. Apparently some of these are actually equivalent for Peano continua. --RDBury (talk) 14:32, 3 September 2013 (UTC)
 * Agreed. Unicoherence is the primary notion. The others are just variations on a theme.  Sławomir Biały  (talk) 15:32, 3 September 2013 (UTC)
 * My impression after dabbling in small expansions to these articles is that (despite their currently stubby content) these are distinct topics, each with a big literature, that could easily support separate articles if only we had the expertise and interest in more serious expansion. —David Eppstein (talk) 01:26, 4 September 2013 (UTC)
 * You've certainly done an excellent job fleshing out Dendroid (topology).  Sławomir Biały  (talk) 00:28, 8 September 2013 (UTC)

When I was an undergraduate I was shocked when I first found out that some literate people had never heard of topology and didn't know that it is a mathematical discipline. But it's a fact: most educated people seeing the word "topology" don't know what it is and don't know that you're talking about mathematics. Nothing in the first sentence of this article attempted to acquaint the lay reader with the fact that matheamtics is what it's about. I changed that.

One should not begin an article that says "In topology,..." unless it says something like "In topology, a discipline within mathematics,...". "In geometry,..." or "In arithmetic,..." or "In algebra,..." or "In calculus,..." etc. are fine. If the article is titled "Monster (mathematics)", or "arithmetic of ordinal numbers" or "Boolean algebra" or the like, then such initial context setting should usually be considered redundant. Michael Hardy (talk) 22:10, 3 September 2013 (UTC)


 * But a reader doesn't need to know it's mathematics, and if they ask themselves what field topology is, that is, who studies it and comes up with these things, they will find that out anyway, from the article on the subject. What they need to know the subject for is so they have context for what's being discussed without depending on familiarity with the words used and what they describe - we are talking spheres and tori, for instance, when we say "n-manifold" in this article - and simple taxonomical navigation. What if you don't know geometry's part of mathematics, but you know or care what the platonic solids are? How are you hindered from learning about geometry at that stage? If it did, I think that would override the want for a shorthand that is acceptable as long as you assume common knowledge of the subjects in the typical math curriculum. In fact, I think that's one of the most important realizations you can have about math, that geometry is the same field as the one where you count, but that's not what you read when you're learning your platonic solids, your 1D 2D 3D 4D, or your 1-sphere 2-sphere red sphere blue sphere, you read that taxonomically, this is where this goes, and it's not worth much to you that this is so. By the time you can understand what makes these mathematics, you don't so much need a reminder of it on every page. On the other hand, even if it's in the title of the article, when there's no link to the subject containing the thing, the actual interface to the site is broken as far as taxonomic navigation goes, since Wikipedia is navigated link-by-link. Not to mention that redirects to the article silently change the title, and readers have to learn to check where they've been sent for information after being initially confused by being sent to articles that aren't primarily about what they're there for. Plus, it makes the information content of Wikipedia articles - the global manual of style - irregular, and regular article structure is how people learning to edit pick up on article structure. ᛭ LokiClock (talk) 08:42, 7 September 2013 (UTC)


 * As described in WP:CONTEXTLINK, it is appropriate and recommended to provide context for technical terms in the first sentence. Topology is a good example, because it is ambiguous. The term is used in many fields of knowledge, like Geospatial topology, and topology and topography are often confused with each other. Letting the reader know immediately that you are talking about the field of mathematics known as topology helps them frame the rest of the lead and article and allows them to decide if this is the article they are indeed interested in. --Mark viking (talk) 17:09, 7 September 2013 (UTC)

Transversals, angle pairs and angle relationships
I don't know if the discussion on transversals, angle pairs and special angle relationships is still current on vertical angles...

1. I think transversal (geometry) should remain an article on its own particularly as the article parallel (geometry) incorporates both parallel lines and the concept of parallelism (which I personally would consider as needing two separate articles since parallel lines is an elementary concept (and should include mention and examples of slope and systems of two equations in two unknowns) and parallelism is a much more advanced concept).

However,


 * a. I think we need to extend transversal (geometry) to include images and definitions of corresponding and alternating angle pairs see e.g.. I have svg images (with many thanks to User:Maschen for his help in learning inkscape) for this on Parallel lines - Transversals)


 * b. Also, since transversals of non-parallel lines have no significant properties, perhaps only a mention of this and at most one image.

If nobody objects, I will do this.

2. With respect to the other mergers of the pages like vertical angles, I would vote for separate articles and something like the Angles template - mk we have on the macedonian wikipedia which is at the top right of any of the pages like this Supplementary angles - mk so that a user can easily see the special angle relationships available.

Lfahlberg (talk) 08:54, 8 September 2013 (UTC)


 * These all look like reasonable changes. Instead of parallel, which is a disambiguation page, perhaps you mean Parallel (geometry)? --Mark viking (talk) 11:54, 8 September 2013 (UTC)


 * Yes about page link. Fixed now. Thanks.Lfahlberg (talk) 12:52, 8 September 2013 (UTC)


 * The term transversal actually has nothing to do with the lines being parallel or not. It's just that historically several theorems connected to parallel lines are stated in terms of transversals. The propositions of Euclid mentioned in the article talk about conditions on the angles of a transversal which imply that the lines are parallel, these make no sense if you think the lines are already parallel. As mentioned in the article as well, the original formulation of Eulcid's fifth postulate is a statement about when the lines in a transversal are not parallel. In addition Menelaus' theorem is basically a theorem on transversals of nonparallel lines. So I disagree with the assessment that there is nothing interesting about transversals of nonparallel lines. Having only, or even a majority of images with parallel lines would be be misleading as best; unfortunately with the way geometry is currently taught in high schools, most readers will already have some misconceptions about this and these should not be reinforced.
 * I agree that articles on complimentary and supplementary angles might be merged, but these really have nothing to do with transversals. --RDBury (talk) 15:16, 8 September 2013 (UTC)

1.Transversals and the Transversal (geometry) page

I very much agree that we need to be extremely careful that we do not teach our children incorrectly and think that “mathematical vagueness” is an incredible source of confusion. So as not to bore people here (too late :)), I have put my suggestions for this page in the talk page there.

I will say here that I agree that it is important to define a transversal properly (as it is done in the page) and then state (something like)
 * In Euclidean geometry, Euclid’s parallel postulate guarentees that two lines are parallel only if the interior non-adjacent angles on the same side of any transversal are supplementary.

In this way, we avoid the chicken/egg problem that RDBury mentions.

2. Angle pairs

Angle pairs such as vertical, complementary,… as well as the angle pairs of transversals (alternating, complementary) are very important and I would venture to state that most children are required to learn these terms and since children (and most adults) have short attention spans, I think the pages explaining these terms should be short and separate. However, we could add a template such as I have created here so that they can easily navigate…

Lfahlberg (talk) 06:44, 9 September 2013 (UTC)


 * I was just looking at the links above thinking about how the articles might be better organized. I've worked on Right angle; there may be too much overlap with Orthogonality and Perpendicular, but I think the fact that Euclid used the right angle as the basic unit for measuring angles gives it enough historical interest for it to have its own article. Of the three Perpendicular is in the most need of attention and could probably be merged with Orthogonality. Interior and Exterior actually map to Internal and external angle, also rather stubby and most of what is there is already covered in Polygon. Adjacent angles, Complementary angles, and Supplementary angles are stubs and there is overlap in what is there. Imo the material could easily be merged with Angle. Dihedral angle isn't a stub but it's close. There a bunch of material in there which more properly belongs in a chemistry article such as Molecular geometry. Even without that the article probably has enough in it to keep it as a separate article, but it needs to be expanded. Transversals have enough historical significance that I think they should have their own article. Specifically, they are the subject of several propositions of Euclid that we should cover somewhere and don't seem to fit anywhere else. Similarly if there is enough material that could be added to one of the stubs then I have no problem with having it stay it's own article; the idea is to do something about articles with almost as much merge and unsourced banner as actual article.
 * On a slightly different note, would it be useful to create a Glossary of geometry, modeled after Glossary of graph theory? --RDBury (talk) 22:10, 9 September 2013 (UTC)

ProofWiki template
I created Template:ProofWiki for links to Proof Wiki. If no one has objections I'll convert existing links and add more. --RDBury (talk) 15:24, 12 September 2013 (UTC)

The 7 Number periodic Cycle( 1 cycle).jpeg & The 7 prime periodic number.jpg
image:The 7 Number periodic Cycle( 1 cycle).jpeg has been nominated for deletion. It also exists on Commons as file:The Cycle of 7.jpg. I can't make heads or tails of the description either here or on commons, so you may want to improve the description of the commons version. -- 70.24.249.39 (talk) 09:37, 16 September 2013 (UTC)


 * It is not explained very well, but it is referring to the well-known fact that 1/7 = 0.142857142857... and 2/7 = 0.285714285714... and 3/7 = 0.428571428571... and 4/7 = 0.571428571428... and 5/7 = 0.714285714285... and 6/7 = 0.857142857142... . The same six digits cycle in the same order, just the starting point depends on the numerator of the fraction. JRSpriggs (talk) 09:56, 16 September 2013 (UTC)


 * Ok, I thought he was claiming that the fractions were transcendental and never repeated a digit, which didn't make sense (there being only 10 digits, which necessitates repetition after using 10 decimal places). -- 70.24.249.39 (talk) 12:08, 16 September 2013 (UTC)

The same problem description occurs with file:The 7 prime periodic number.jpg (up for deletion) and commons:file:The 7 prime periodic number.jpg. -- 70.24.249.39 (talk) 08:15, 17 September 2013 (UTC)

HI, THIS IS FROM ME AS THE FOLLOWING: — Preceding unsigned comment added by KAMAL2 (talk • contribs) 08:36, 23 September 2013 (UTC) Yes. This means we have digits 0,1,2,3,4,5,6,7,8,9 which are the decimal system. So, the six digits repeating for all fractions of 7 are: 1, 4, 2, 8, 5, and 7 which are a part of the ten digits above but unique with no repetition excluding 0,3,6, and 9 which are multiple of 3. Also, these six digits above are the same for all 1/7, 2/7, 3/7, 4/7, 5/7, and 6/7 with shifting of digits making a new order of the fractions 1/7, 3/7, 2/7, 6/7, 4/7, and 5/7 (cyclic). These digits were not known they are the same the fractions numbers of 7. — Preceding unsigned comment added by 109.73.245.55 (talk) 08:34, 23 September 2013 (UTC)

Fourier coefficients
Fourier coefficients redirects to a section of Fourier series, and until recently, Fourier coefficient redirected to the article as a whole, not to a section. Someone has made Fourier coefficient into a stubby new article, but did not redirect the plural to the singular. What is the best course at this point? (My inclination would be to redirect both either to Fourier series or to a section of that article.) Michael Hardy (talk) 20:04, 17 September 2013 (UTC)
 * Given the current state of Fourier coefficient, I think it would be best to have it redirect to the same section of Fourier series. That section covers the topic better than the new article, so having a separate article is pointless unless someone wants to make major improvements to it. —David Eppstein (talk) 20:34, 17 September 2013 (UTC)

(In case anyone wondered, I made the change suggested by David Eppstein above.) Michael Hardy (talk) 17:14, 24 September 2013 (UTC)

Iterated limits and interchanges
We have a section titled Limit_of_a_function; we have an article titled Interchange of limiting operations, which quotes G. H. Hardy as saying "The problem of deciding whether two given limit operations are commutative is one of the most important in mathematics" but which is severely short of examples or results, let alone an explanation of why it's considered so important; and we have Iterated limit, which was a mess until I totally rewrote it today, including a change in its title, but which is still deficient. So far, Iterated limit is linked only from the "See also" section of Interchange of limiting operations.

To do:
 * Greatly improve Interchange of limiting operations, including examples of limits, sums, integrals, derivatives, etc. This doesn't just mean interchanging two integrals or two sums or two derivatives or two limits; it also includes interchanging a limit with a sum, a derivative with an integral etc.  And at least state some theorems.
 * Further work on Iterated limit. Maybe at least one theorem saying if the joint limit exists then so do the two iterated limits, and they're equal?
 * Links to these articles from other articles.


 * Might some mergers or reorganizations be in order?

Michael Hardy (talk) 17:12, 24 September 2013 (UTC)

Wikipedia_talk:Articles_for_creation/Murray_polygon
Hi, this article is up for review at Articles for creation and I would be grateful if any advanced geometrists could cast their eyes over it. Rankersbo (talk) 18:52, 25 September 2013 (UTC)


 * It's not clear to me from the references provided that the concept is notable, since all but one of the references are to articles by the original inventor of the concept.


 * The mathematics seems sound.


 * The article has some confusing portions. For example, when defining addition the article does not say what ai and bi are (it might be considered clear from the context, but it would be better to be explicit).  The use of Gray codes is not very clear; I think there should be further explanation of the Gray coding algorithm.  Also, I was confused the first time I read the example: It immediately follows the introduction of Gray coded murray integers but is not about Gray coded murray integers, only ordinary murray integers.  Perhaps Gray coding of murray integers would be better in a subsection of their own.  Lastly, the article mentions more efficient algorithms for traversing curves, and I would like to see a little more detail about them.


 * Ozob (talk) 19:17, 25 September 2013 (UTC)
 * I found articles in Google scholar involving this subject by at least three groups, so I think it may be marginally notable — good enough that I wouldn't try to get it deleted but also wouldn't put a lot of effort into getting it created. I agree with your criticisms of the current draft. I'd also like to see a little more on the applications — not so much the primary sources saying that it can be used for these applications, although a little more detail on how it's used would be helpful, but I'm more interested in secondary sources (if they exist) comparing it to other approaches for these applications. E.g. there are a lot of ways to dither. What makes this one stand out? —David Eppstein (talk) 19:31, 25 September 2013 (UTC)
 * Also, the definition is incomplete: it should be said that the murray integer $$[d_n,\ldots,d_1]$$ represents the integer $$d_1+r_1d_2+r_1r_2d_3+\cdots$$, or in Horner notation $$ d_1+r_1(d_2+r_2(d_3+r_3(\ldots))).$$ D.Lazard (talk) 20:40, 25 September 2013 (UTC)
 * It looks like much of the article is devoted to the mechanics of variable base notation, which is (or should be) already covered in Mixed radix. It would probably be better to add the curve material to it rather than have a separate article. --RDBury (talk) 23:57, 27 September 2013 (UTC)

please lend your support to this new Individual Engagement Grant: Towards a PlanetMath Books Exchange
Please lend your support to this Individual Engagement Grant proposal I've put together with PlanetMath contributor Raymond Puzio. Inspired by the PlanetMath Exchange project, our aim with this proposal is to improve the PlanetMath platform and make it easy to produce free/open mathematics textbooks -- and export to places like Wikibooks. Your endorsement of the grant proposal would mean a lot! And any comments prior to the Sept. 30, 2013 deadline will help us improve the proposal. --Arided (talk) 22:30, 27 September 2013 (UTC)


 * The link does not work. Boris Tsirelson (talk) 06:14, 30 September 2013 (UTC)
 * @Tsirel: Fixed. --Arided

Infobox conic section
Infobox conic section has been nominated for deletion -- 65.92.181.39 (talk) 04:03, 28 September 2013 (UTC)

Infobox Complexity Class
Infobox Complexity Class has been nominated for deletion -- 65.92.181.39 (talk) 05:01, 30 September 2013 (UTC)