Talk:Singularity (mathematics)

message: The example of the absolute value function having a singularity at x=0 might not be the best, because the absolute value function is not complex differentiable anywhere.
I don't understand the sentence:
 The algebraic set defined by y2 = x also has a singularity at (0,0), this time because it has a "corner" at that point. 
As a set in the plan (i.e., as an imbedded 1-manifold) it is perfectly well behaved. Thought of as a (multi-valued) function it has an infinite slope. 
Per haps "... because it has a vertical tangent at that point."
Maybe I'm missing something, which is why I didn't just make the edit myself.... Better not to be bold and confused at the same time. ;-> Jeff 01:40 Apr 10, 2003 (UTC)
:Yeah, I deleted the y2=x example, because it's just a sideways parabola. It doesn't have any undefined areas, or anything else that could be considered singularities. If you count the negative x values, maybe, but that wasn't included in the example.
:There's other bad examples. Like y=|x|. You can take the absolute value of zero, right? Isn't it just zero?  — Preceding unsigned comment added by 50.5.96.209 (talk) 17:03, 20 May 2017 (UTC)
replies: text: It would be better to have that as disambiguation, I think. Singularity of a function would be one alternate name. There is also singularity of a differential equation to think about. Charles Matthews 19:14, 12 Apr 2005 (UTC)
thread_title: Comments

message: A lot of these seem to be closely linked.
Start with a function f : Rm -> Rn. The first derivative
dfˈis a linear map or an m by n matrix. f will be singular (in terms of algebraic geometry/singularity theory) when the matrix drops rank. (i.e. is singular).
The commutative algebra ideal's are generilisations of this concept, (think of the ideal generated by the derivatives).
Likewise the singular solutions of ordinary differential equations are simarly linked. --Salix alba (talk) 11:53, 25 January 2006 (UTC)
thread_title:  Connections 

message: There are more than four types of singularities in Complex Analysis.  I will correct this mistake if there is no disagreement on this issue.  Furthermore, ranking them is appropriate, as the differences are significant.  Tparameter 05:53, 9 December 2006 (UTC)
thread_title:  Number of Types of Singularities in Complex Analysis 

message: I (physicist) don't understand what U \ {a} means. Perhaps somebody who does could add a link to something which explains it? Or make it more explicit/obvious? It's in the Complex Analysis section. Thanks --213.49.250.152 (talk) 18:22, 29 July 2009 (UTC)
replies: text: It means the set U without the element 'a.' (though, 'a' need not be a member of the set U. In which case U\{a} = U.) Got it? I don't think we should change it. It's very common math notation. futurebird (talk) 07:38, 20 September 2010 (UTC)
thread_title:  Notation 

message: Could someone explain what it is that is single that prompts the name "singularity? Gwideman (talk) 00:21, 20 September 2010 (UTC)
replies: text: if you take the second definition of singular Being the only one of the kind; unique. It most common for a singularity to occur at an isolated point, 1/x has a unique point at 0, which has different behaviour to all other points, hence is singular or a singularity.--Salix (talk): 06:48, 20 September 2010 (UTC)
replies: text:  I have never thought of this before but it makes a lot of sense. I wonder if we can source it? futurebird (talk) 07:39, 20 September 2010 (UTC)

text:  Thanks, Salix, for the reply. I had indeed speculated about that being the origin of the term, but it seems a little indirect -- especially since a function might well have more than a single singularity. So like Futurebird I'm wondering if there's an authoritative source for that account? Gwideman (talk) 21:54, 25 September 2010 (UTC)
replies: text:  One of the meanings of the French word singulier is "curious, strange, peculiar". This explains the use of "singularity". However, the Latin singulāris has also the meaning of "unusual". So, I do not know whether "singularity" is derived from the Latin or the French word. In any case, the only relation between "singularity" and "single" is to be cognates. D.Lazard (talk) 13:16, 5 September 2022 (UTC)
thread_title:  Etymology: What is the "single" that "singularity" refers to? 

message: This
: The function g(x) = |x| (see absolute value) also has a singularity at x = 0, since it is not differentiable there. Similarly, the graph defined by y2 = x also has a singularity at (0,0), this time because it has a "corner" (vertical tangent) at that point. 
As the section on real analysis says: A point of continuity, which is not a singularity, is a value of c for which f(c − ) = f(c) = f(c + ). Why is the intro using a different defn for the meaning of the word, and where does it get it from?
seems odd to me. I think |x| has no singularities, but its derivative has one at 0. Ditto, y2=x. And calling a vertical tangent a corner is odd, too William M. Connolley (talk) 11:02, 31 December 2010 (UTC)
thread_title:  Meaning of the word 

message: I believe this voice is flawed. It keeps on confusing two concepts which should not be confused, at least here! Singularities and discontinuities are not the same: though it may be true that every discontinuity is alaso singular point (depending of the concept of "well-behavedness" you have), the converse certainly is not. y=1/x has a singular point at {0}, but it's a continuos funtion - hence it can't have any discontinuities. The fact is that discontinuity is a domain-related concept: it has no sense to discuss about continuity in points which not belong to the domain of the given function. On the contrary, singularity is a concept always referring to a broader set than the domain (with the limit case of this broader set = domain): a continuos function may be singular in some extension of its domain (again, y=1/x is continuos in its domain R-{0}, but singular in R}.
I think the entry should be fixed, and made coherent with the content of http://en.wikipedia.org/wiki/Classification_of_discontinuities which seems to be more precise.  — Preceding unsigned comment added by 151.55.58.176 (talk) 16:28, 11 July 2012 (UTC)
thread_title:  Singularity and discontinuity are not the same 

message: 67.252.103.23 (talk) 17:46, 14 March 2014 (UTC)
replies: text: exists already as a redirect to this article. I agree with moving Mathematical singularity to , because "mathematical singularity" is a terminology which is rarely used. However, this move can only be done by an administrator and needs thus a request for move. I'll support such a request. D.Lazard (talk) 19:57, 14 March 2014 (UTC)
thread_title:  Change to Singularity (mathematics) 

message: Division by zero is only undefined in certain circumstances. I mean to make the article reflect the true nature of reality, which is that there are many structures where you can divide by zero and get a defined result. 💗
96.227.223.203 (talk) 17:24, 13 September 2023 (UTC)
replies: text: Wikipedia is not the place for publishing your original research. Moreover, every addition must be the object of a consensus of the community of Wikipedia editors. As you have been reverted by two different editors, there is no consensus for yours edits, and they are not welcome in Wikipedia. D.Lazard (talk) 17:46, 13 September 2023 (UTC)
replies: text: Back off. I'd be pleased if I were the one to first claim that division by zero is defined, but I am not. There are many before me, such Bernhard Riemann, Anton Setzer, Jesper Carlstrom, Brahmagupta, John Wallis, Isaac Newton, Augustus De Morgan, and Leonhard Euler. 96.227.223.203 (talk) 18:56, 13 September 2023 (UTC)
replies: text: Calling this "original research" is indeed a stretch and a red herring, but it's also not very helpful for this article, and the people reverting it are not "harassing" you. There are plenty of articles either currently discussing or which could plausibly discuss possible definitions of division by zero, starting with.... division by zero, but also including projectively extended real line, Riemann sphere, zeros and poles, homogeneous coordinates, point at infinity, wheel theory, etc. There's even a discussion of poles in this article in the section . We don't need to have such a discussion literally everywhere that the reciprocal function appears on Wikipedia, and in particular it is a distraction in the context of the lead section of this article. –jacobolus (t) 03:44, 14 September 2023 (UTC)
thread_title:  Division by zero 💗