Talk:1 + 2 + 3 + 4 + ⋯/Archive 1

Archive 1

Archive 2

Merge

Why don't we merge the mathematically interesting results of this series with their respective articles and then just use this page as a redirect or disambig.--Cronholm144 22:22, 12 May 2007 (UTC)

Why would we do that? Melchoir 09:13, 13 May 2007 (UTC)

well because this article as it stands now doesn't really meet the standards for article inclusion. I know you are attached to divergent series, but every one doesn't deserve an article--Cronholm144 09:16, 13 May 2007 (UTC)

What standards would those be? Melchoir 09:51, 13 May 2007 (UTC)

Cronholm144, I have a couple of suggestions: (i) it would help if you were more specific about which article or articles you are proposing to merge this page into - it is difficult to respond usefully to a very generic proposal; (ii) if you wanted a wider response to your various merge proposals around divergent series, you could outline your arguments at Wikipedia talk:WikiProject Mathematics. Gandalf61 10:05, 13 May 2007 (UTC)

I am aware of this, all of my comments were made as I was working in a different vein, I did not realize that there were dedicated editors behind all of these articles. I have left my last word on the topic on Melchoir's talk page.--Cronholm144 10:10, 13 May 2007 (UTC)

Medium term organisation

Although 1-2+3-4+... generated some controversy, I was happy that it was featured, as I am a big fan, and have already expressed that in its maths rating. Cronholm's recent reaction to these articles on divergent series was rather hasty, but despite this, I do think there is case to be made for some reorganisation. Although Wikipedia is a work in progress, it is also a work in use, and Cronholm's experience may reflect a more general reader's reaction. I do not think these articles are in conflict with WP:NOT (an indiscriminate collection of information) but other readers and editors may not agree. I therefore wonder if there is not something to be gained by pooling some of the resources in these articles, at least while they undergo further development.

As far as I can tell, these articles can be discriminated in two ways. First, there is the contrast between divergent geometric series and divergent series with zeta and eta function regularization. Second, there is the contrast between series with alternating signs, and those without. At the very least, this suggests to me that this article could usefully be merged with 1 + 1 + 1 + 1 + · · · which at present adds little further information other than an anecdote.

Similarly, I see no reason why the divergent geometric series examples could not be merged, with the exception, of course, of Grandi's series, which deserves its own article (and also the 1 + 1 + 1 + 1 + · · · anecdote is more appropriately covered in the zeta-function context). Such a merger could take place either within the article itself, or in a separate article on examples of divergent geometric series. I look forward to hearing your views. Geometry guy 23:51, 13 May 2007 (UTC)

I can certainly see 1 + 2 + 3 + 4 + · · · and 1 + 1 + 1 + 1 + · · · being merged, as it is extremely hard to find a source that says anything about one of those series without naturally applying to the other. Even primary sources like Euler and Ramanujan seem to lump them together.

I could also understand 1 + 2 + 4 + 8 + · · · being merged into Divergent geometric series, because there is almost no mathematics that applies to 1 + 2 + 4 + 8 + · · · but not equally well to other geometric series. Most of that can be found at Two's complement anyway. However, you'd really have a devil of a time trying to shoehorn 1 − 2 + 4 − 8 + · · · in as well. That series has a special history; it can be Euler- and Borel-summed, which doesn't work for positive series; and the particular ease of Euler summation is unique. Melchoir 02:21, 14 May 2007 (UTC)

Thanks for this helpful and expert answer! This is worth thinking more about, I believe, but for me it will have to be tomorrow. Geometry guy 02:38, 14 May 2007 (UTC)

Proof by Induction

One of the proofs I like, is the proof by induction showing (1/2)n(n+1) + n+1 is equal to (1/2)(n+1)(n+2). Hope that makes sense.--138.253.162.174 (talk) 17:18, 26 November 2008 (UTC)

Well duh, (1/2)n(n+1) + (n+1) is equal to ((1/2)n+1)(n+1), which is equal to (1/2)(n+2)(n+1). Besides, what does this has to do with 1 + 2 + 3 + 4 + ... 24.1.201.172 (talk) 01:20, 22 May 2010 (UTC)

Don't get it...

Isn't 1 + 2 + 3 + 4 + · · · equal to the Cauchy product of 1 + 1 + 1 + 1 + · · · with 1 + 1 + 1 + 1 + · · · ? If so, 1 + 2 + 3 + 4 + · · · = ^-1⁄₂·^-1⁄₂ = ¹⁄₄. I must be missing something... JocK 20:55, 2 July 2007 (UTC)

I think this just shows that methods of summing divergent series do not in general commute with the Cauchy product. So sum of Cauchy product $\neq$ product of sums. Gandalf61 08:39, 3 July 2007 (UTC)

On an even more basic note, the article begins without any context. Someone with a basic knowledge of high school mathematics will likely understand most of the terms and symbols in the first section, but will be utterly bewildered by the statement that a sum of positive numbers yields a negative result. A sentence or two addressing this confusion would be very useful and important. See the article "Zeta Function Regularization", which appropriately places 'sum' in quotation marks. — Preceding unsigned comment added by 128.138.141.214 (talk) 21:20, 4 May 2012 (UTC)

Inadequate explanation

The statement in the lead that 1+2+3+4+... sums to a definite result and that this sum of positive terms is a negative number (-1/12) is not just "interesting". It is spectacularly and wonderfully counter-intuitive to readers not already versed in the Riemann zeta function (i.e. to virtually all Wikipedia readers). This would be a fascinating article if it delivered a good explanation of this result. Why doesn't it? By contrast, the article on 1-2+3-4+5+... does an excellent job (illustrations and all) of presenting a counter-intuitive result in a manner that requires nothing more of the reader than some basic junior high school level algebra.

In the already crowded field of Wikipedia math articles that have great potential but blow it on opaque text that is incomprehensible to readers without a university math degree, this one must surely be in the top 10. --Ross Fraser (talk) 00:00, 20 July 2012 (UTC)

January 2014 traffic

The traffic for this month is shown at http://stats.grok.se/en/201401/1_+_2_+_3_+_4_+_⋯. Starting from January 9, traffic is 4000 views/day, which I assume is due to Numberphile's video at https://www.youtube.com/watch?v=w-I6XTVZXww. Then, January 17 caught an additional 10,000 views. Does anyone know what caused the latter spike? Melchoir (talk) 03:18, 18 January 2014 (UTC)

I think is just the spread of the numberphile video, being mentioned a lot. EG BoingBoing, slate. --Salix alba (talk): 06:52, 18 January 2014 (UTC)

Good to know, thanks! Melchoir (talk) 01:42, 28 January 2014 (UTC)

Did Euler sum this series?

There are plenty of authors who claim that Leonhard Euler wrote that 1 + 2 + 3 + 4 + ⋯ = −1/12, including some of the links in the "External links" section. And yeah, okay... it does sound like something Euler might have written. However, the claims are always vague about when and where Euler wrote it down, and I can't find the equation in Euler's works!

Does anyone know if Euler really did write down the equation? Or is it nothing more than a rumor? Melchoir (talk) 01:42, 28 January 2014 (UTC)

Explaining revert

To explain this revert [1], I removed the following prose:

This is not actually a summation, but merely a number describing the series, which indicates that the series is divergent. It is comparable to a derivative, which indicates the slope (not the value) of a line. In the famous formula seen below, the = sign refers to a number which describes the sum, and does not mean "equals" in the traditional sense

1. There's no distinction between the result of a generalized summation method and "merely a number describing the series". Every kind of summation, including the usual definition, is just a number that describes a series. Of course, we do need to distinguish between the generalized sum of −1/12 and the usual definition of summation for convergent series. But I think it's enough to say (in both of the lead paragraphs) that the series diverges and to put "sum" in quotation marks.
2. The comparison with a derivative is a very interesting idea, since regularizing a sum can be thought of as picking out the constant part of an expansion in some parameter, just as the derivative picks out the linear part of the Taylor expansion. However, the analogy is also misleading, since a function with a derivative also has a value; the present series has a regularized sum but not a convergent sum.
3. The "=" sign does mean "equals" as long as the "+ · · ·" on the left-hand side of the equation is interpreted using one of the summation methods in question. In that context, the equation states that the generalized sum is precisely equal to −1/12. Anyway, the cited sources don't say anything about the equals sign.

I'm not saying that the lead is perfect as it stands, either! Clarifications can be made as necessary, and we can subtly tailor the wording to avoid giving calculus students the wrong idea. But we should make sure that we don't hang so many scary caveats on the result that it's drained of all meaning. Melchoir (talk) 06:29, 28 January 2014 (UTC)

-1/12 is NOT the sum of that series. you need to explain a little more clearly why you are putting "sum" inside parantheses. If you don't like my explanation, feel free to EDIT what I wrote... but you shouldn't just delete it. The version you are reverting to provides no explanation whatsoever for why "sum" is not the correct word to use, and its causing confusion leading people to believe the sum of all positive integers is a negative number. that is NOT correct. clearly this article needs more caveats. — Preceding unsigned comment added by 68.185.193.1 (talk • contribs) 09:24, 28 January 2014‎

I think you're exaggerating the situation. The version I reverted to does provide an explanation for why "sum" is not the correct word to use: Because the series 1 + 2 + 3 + 4 + · · · diverges, it does not have a sum in the usual sense of the word. It would be reasonable to say that the explanation is insufficient, but it's disingenuous to say that there's no explanation whatsoever!

The usage of "sum" in the context of generalized summation methods is well-known and can be found throughout Hardy's monograph. For that matter, the word is used in Ramanujan's second letter, which is quoted in the body of the article. All that said, I can see how it could cause confusion in the lead section, so I'll replace it with more specific claims about the particular summation methods used.

In general, my objection about the caveats is that they shouldn't be attached to every single statement. It's just tedious. I'll try restructuring the lead to combine the caveats in the first paragraph. I think this is a reasonable compromise: it should satisfy the need to make the point as forcefully as possible, without spreading FUD to the rest of the content. Melchoir (talk) 20:04, 28 January 2014 (UTC)

Summability > Zeta function regularization > The Last Equation (added within 24 hrs.)

The equation-in-question is as the following:

$-3\zeta (-1)=\eta (-1)=\lim _{x\to 1^{-}}\left(1-2x+3x^{2}-4x^{3}+\cdots \right)=\lim _{x\to 1^{-}}{\frac {1}{(1+x)^{2}}}={\frac {1}{4}}$

Dirichlet Eta function is not continuous at s = -1, therefore it would be incorrect to say:

• $\eta (-1)=\lim _{x\to 1^{-}}\eta (x)$
• $\eta (-1)=\lim _{x\to 1}\eta (x)$
• $\eta (-1)=\lim _{x\to 1^{+}}\eta (x)$

In fact, the last one would be all right. Anyway, the first one wouldn't be all right; hence, it is incorrect to say:

$\eta (-1)=\lim _{x\to 1^{-}}\left(1-2x+3x^{2}-4x^{3}+\cdots \right)$

You could say that "my analytically continued eta evaluates into 1/4 at -1" if you want, but that would not be equal to the sum $1-2+3-4+\cdots$. It would at best be equal to the limit $\lim _{x\to 1^{-}}\left(1-2x+3x^{2}-4x^{3}+\cdots \right)$. All in all, that particular equation is actually:

$-3\zeta (-1)=\eta (-1)\neq \lim _{x\to 1^{-}}\left(1-2x+3x^{2}-4x^{3}+\cdots \right)=\lim _{x\to 1^{-}}{\frac {1}{(1+x)^{2}}}={\frac {1}{4}}$

Thanks for reading. — Preceding unsigned comment added by ThoAppelsin (talk • contribs) 04:32, 1 February 2014 (UTC)

---

Well, there are a couple things going on here. First, the eta function is continuous at s = -1, so it would be correct to say $\eta (-1)=\lim _{x\to 1}\eta (x)$. (Edit February 1: I meant, $\eta (-1)=\lim _{x\to -1}\eta (x)$) However, that's aside from the point. The limit $\lim _{x\to 1^{-}}\left(1-2x+3x^{2}-4x^{3}+\cdots \right)$ is the Abel sum of the (divergent) numerical series $1-2+3-4+\cdots$, which is the (formal) value of the Dirichlet series $1^{-s}-2^{-s}+3^{-s}-4^{-s}+\cdots$ at s = -1. Since the eta function is equal to the Abel sum of that series everywhere, evaluating the limit tells us eta(-1).

Since it's been challenged, I'll go ahead and find a source for this... Melchoir (talk) 04:43, 1 February 2014 (UTC)

...Here's the diff with the references: [2]. Melchoir (talk) 06:35, 1 February 2014 (UTC)

By the way, about continuity at -1, you might have been thinking of the Dedekind eta function. I know I've made that mistake more than once! Melchoir (talk) 08:15, 1 February 2014 (UTC)

---

$\eta (-1)=\left(1-2+3-4+\cdots \right)$

Is that right? If so;

$\eta (-1)=\lim _{x\to 1^{-}}\left(1-2x+3x^{2}-4x^{3}+\cdots \right)$

implies:

$\left(1-2+3-4+\cdots \right)=\lim _{x\to 1^{-}}\left(1-2x+3x^{2}-4x^{3}+\cdots \right)$

which is not true. The 1 − 2x + 3x⋅x − 4x⋅x⋅x + ⋅⋅⋅ is not continuous at x = −1. Dirichlet Eta may or may not be, but the series 1 − 2x + 3x⋅x − 4x⋅x⋅x + ⋅⋅⋅ isn't. — manual signature: comment added by ThoAppelsin (talk • contribs) 15:08, 1 February 2014 (UTC)

Those equations are all true if (1 − 2 + 3 − 4 + · · ·) is interpreted as an Abel sum. But be careful with the notation: the limit $\lim _{x\to 1^{-}}$ is the limit as x approaches 1 from below, NOT the limit as x approaches −1. I'll make that clearer in the article.

The series 1 − 2x + 3x⋅x − 4x⋅x⋅x + ⋅⋅⋅ is convergent for −1 < x < 1. On that interval, the sum of the series is 1/(1 + x)². The limit as x approaches −1 does not exist. But the limit as x approaches 1 does exist, and it equals −1/4. By definition, then, this is the Abel sum of the series 1 − 2 + 3 − 4 + · · ·. Melchoir (talk) 20:25, 1 February 2014 (UTC)

What does "the limit as x approaches 1 from below" mean? My guess is that it means "the limit as x approaches 1 from left or from lower values", could also be below I guess, if we tilt our heads 90° clockwise. If it does not mean anything else than my guess, then the notation was all clear from my point. Actually, I have to say that it used to be clear with that good old notation, and not so much anymore; it is the first time I am seeing the notation that is currently being used.

I concur with the first three sentences. However, as it is in the third sentence, in the fourth sentence, expression you are referring to is unclear to me. With "But the limit as x approaches 1 does exist, and it equals −1/4."; if you referring to the expression 1⁄(1 + x)², then it is all right; if you are, however, referring to the expression 1 − 2x + 3x⋅x − 4x⋅x⋅x + ⋅⋅⋅, then sentence #4 is incorrect. The reason why I can concur with the third sentence despite being uncertain about its reference, is that it is true for both of the expressions. — manual signature: comment added by ThoAppelsin (talk • contribs) 23:10, 1 February 2014 (UTC)

It's a well-known problem that a string of written symbols can represent either a formal series or the sum of that series. The meaning is determined by context. In this case, when I equate the limit of an expression with a number, we can conclude that the expression must represent a function R -> R. This function is the sum 1 − 2x + 3x⋅x − 4x⋅x⋅x + ⋅⋅⋅, AND it equals 1⁄(1 + x)² for all x in an open set of the form (1-epsilon, 1).

Anyway, I think we're straying from discussing the article. It currently states:

$-3\zeta (-1)=\eta (-1)=\lim _{x\nearrow 1}\left(1-2x+3x^{2}-4x^{3}+\cdots \right)=\lim _{x\nearrow 1}{\frac {1}{(1+x)^{2}}}={\frac {1}{4}}$

Do you have a suggestion relating to those equations? Melchoir (talk) 23:36, 1 February 2014 (UTC)

I do:

$-3\zeta (-1)=\eta (-1)={1}-{2}+{3}-{4}+\cdots \neq \lim _{x\nearrow 1}\left(1-2x+3x^{2}-4x^{3}+\cdots \right)=\lim _{x\nearrow 1}{\frac {1}{(1+x)^{2}}}={\frac {1}{4}}$

— manual signature: comment added by ThoAppelsin (talk • contribs) 23:53, 1 February 2014 (UTC)

Are you claiming that $\eta (-1)={1}-{2}+{3}-{4}+\cdots$? Melchoir (talk) 00:04, 2 February 2014 (UTC)

I am. — manual signature: comment added by ThoAppelsin (talk • contribs) 00:40, 2 February 2014 (UTC)

Well, there's the problem. How do you define the right-hand side? Melchoir (talk) 00:46, 2 February 2014 (UTC)

Addition of the numbers that follow the rule n⋅(−1)ⁿ⁺¹, starting with n = 1, increasing n by one for each subsequent number, doing this till forever. The variable a in the following would be it, though I don't think int would be able to contain that. Maybe a long long int... nah, that probably wouldn't make it either...

int main ( ) {
  int a = 0, b = 0, c = -1;
  while( 1 ) {
    b ++;         /* increase b by 1     */
    c *= -1;      /* multiply c with -1  */
    a += b * c;   /* increase a by b * c */
  }
}

— manual signature: comment added by ThoAppelsin (talk • contribs) 01:12, 2 February 2014 (UTC)

That's not helpful. Let me just compare the two kinds of summation that are involved here. To heighten the contrast, I'll write u() for the usual sum of a series and A() for the Abel sum of a series. Then for Re(s) > 0, we have

$\eta (s)=u(1^{-s}-2^{-s}+3^{-s}-4^{-s}+\cdots ).$

However,

$\eta (-1)\neq u(1-2+3-4+\cdots )$

because the right side is undefined, and

$u(1-2+3-4+\cdots )\neq \lim _{x\nearrow 1}u\left(1-2x+3x^{2}-4x^{3}+\cdots \right)$

because the left side is undefined. If we were so inclined, we could write these two non-equations on the same line:

$\eta (-1)\neq u(1-2+3-4+\cdots )\neq \lim _{x\nearrow 1}u\left(1-2x+3x^{2}-4x^{3}+\cdots \right)$

But that doesn't really get us anywhere. On the other hand, switching to Abel summation, for all s, we have (see Knopp p.491)

$\eta (s)=A(1^{-s}-2^{-s}+3^{-s}-4^{-s}+\cdots )$

and by definition of the Abel sum,

$A(1^{-s}-2^{-s}+3^{-s}-4^{-s}+\cdots )=\lim _{x\nearrow 1}u\left(1^{-s}-2^{-s}x+3^{-s}x^{2}-4^{-s}x^{3}+\cdots \right).$

Putting the previous two equations together,

$\eta (s)=\lim _{x\nearrow 1}u\left(1^{-s}-2^{-s}x+3^{-s}x^{2}-4^{-s}x^{3}+\cdots \right).$

In particular, by taking s = −1, we get

$\eta (-1)=A(1-2+3-4+\cdots ).$

Meanwhile, by definition of the Abel sum,

$A(1-2+3-4+\cdots )=\lim _{x\nearrow 1}u\left(1-2x+3x^{2}-4x^{3}+\cdots \right).$

Putting the previous two equations together,

$\eta (-1)=\lim _{x\nearrow 1}u\left(1-2x+3x^{2}-4x^{3}+\cdots \right).$

This amount of repetition and extra notation would be way too much to add to the present article. I write it here to clarify the above discussion. Melchoir (talk) 02:55, 2 February 2014 (UTC)

Until the part "But that doesn't really get us anywhere." I am all good, but then this explanation takes one detour from the right, leaving me on the main track because I am not familiar with the waypoints it's trying to give me. I have and already actually had looked up for the "Abel Sum", and the best I've got is Abel's summation formula, which I cannot relate to this. Then I checked the Knopp p.491, which (unless I am looking at something different here) only says that this is equal to this, and that is equal to that. There also is a disclaimer on top that it won't deal much with proofs or anything. Maybe it tells more than this, but it fails to deliver those points if they exist, or at least it fails to deliver those points to me.

As said, it doesn't get us anywhere, and it shouldn't really, because it doesn't go anywhere in particular itself. What is this "Abel Summation"? If it is not a summation in the world of mathematics where 2 + 2 = 4, why are you ascribing and why shall I ascribe any importance to it? Sincerely speaking, shouldn't simply any calculation, summation method, what-so-ever be dismissed as soon as it claims that adding up 1, 2, 3 and so on would end up with something, when applied with regards to all its guidelines?

I guess this is the end, I don't think I will be getting a reasonable, but truly reasonable, explanation to what Abel Summation is or how this switching can happen. The detour will be a mystery for me, I won't deal with it and take it as a truth, but I can take it as a belief that many Doctors of Philosophy choose to believe in, and will try to respect their beliefs. — manual signature: comment added by ThoAppelsin (talk • contribs) 03:57, 2 February 2014 (UTC)

There's a short descripiton at Divergent series#Abel summation, which Abel summation currently redirects to. It should probably be a separate article, but I guess no one's gotten around to writing it. (You could try requesting it at Wikipedia:Requested articles/Mathematics#Complex analysis.) About switching between methods in general, there are various abelian and tauberian theorems that relate different summability methods. In the case of the Dirichlet eta function, the important result is kind-of sort-of in the spirit of an abelian theorem: Abel summation of its Dirichlet series gives you an analytic function on the whole complex plane, which implies that it's consistent with any other method of analytic continuation: it truly is the Dirichlet eta function. This is basically a modern, rigorous way of restating Euler's results.

Speaking of Euler, at one point he anticipated certain aspects of the modern attitude toward divergent series. He didn't anticipate that there would be several inequivalent methods, but he did address whether or not his divergent "sums" should be called "sums", given that they sometimes looked absurd. He concluded that it didn't matter, as long as they were useful! See De seriebus divergentibus, especially sections 6 through 10. He mentions 1 + 2 + 3 + 4 + ⋯, but only in passing, as a series related to 1 + 2 + 4 + 8 + ⋯. Although he doesn't focus on 1 + 2 + 3 + 4 + ⋯, it might be possible to say something about his argument in this article. I'm not sure how to fit it in, but anyone is welcome to try! Melchoir (talk) 05:10, 2 February 2014 (UTC)

Summability > Summary part: Incorrect statement

"[...] Those methods [Cesàro Summation & Abel Summation] work only on oscillating series; they cannot produce a finite answer for a series that diverges to +∞. [...]"

This sentence makes 2 statements for 2 methods, 4 statements in total:

• (A) Cesàro Summation works only on oscillating series.
  • (B) Thus, Cesàro Summation cannot produce a finite answer for a series that diverges to +∞.
• (C) Abel Summation works only on oscillating series.
  • (D) Thus, Abel Summation cannot produce a finite answer for a series that diverges to +∞.

Follow-ups are all right, if A is correct, B also is, since a series that diverges to +∞ may not be oscillating, same for C and D.

However, I don't know about the C, but the statement A itself is not correct. Cesàro Summation does work for series that do not oscillate, as long as the series do not diverge. For example, it works for the series ∑(1/2)ⁿ, sequence of which starting with a₁:

${\begin{aligned}\\S_{n}&=\textstyle \sum _{k=1}^{n}1/2^{n}\\S_{n}&=1-1/2^{n}\\\\CesSum&=\lim _{b\to \infty }{\frac {\textstyle \sum _{n=1}^{b}S_{n}}{b}}\\CesSum&=\lim _{b\to \infty }{\frac {\textstyle \sum _{n=1}^{b}(1-1/2^{n})}{b}}\\CesSum&=\lim _{b\to \infty }{\frac {b-\textstyle \sum _{n=1}^{b}(1/2^{n})}{b}}\\CesSum&=1-\lim _{b\to \infty }{\frac {\textstyle \sum _{n=1}^{b}(1/2^{n})}{b}}\\CesSum&=1-\lim _{b\to \infty }{\frac {S_{b}=CesSum={\mbox{with the assumption that it is bounded}}}{b}}\\CesSum&=1-0\\CesSum&=1\end{aligned}}$

My suggestion: Adding "Excluding/aside from the convergent series," right at the beginning of that sentence, assuming that Abel thing works out for the convergent non-alternating series as well. Else, some other formulation... — manual signature: comment added by ThoAppelsin (talk • contribs) 14:39, 2 February 2014 (UTC)

Good point. Does this work? [3] Melchoir (talk) 19:20, 2 February 2014 (UTC)

It does work for me, but the critical side of me wants me to say that this may get misunderstood by people who think like a computer. "convergent series and oscillating series" does seem to imply convergent series ∨ oscillating series in logic or convergent_series | oscillating_series in C (bitwise), thanks to repeated mentioning of the word "series". Chance of misunderstanding would even be higher if it was worded as "Those methods work only on convergent and oscillating series; [...]", but I don't know, would it look bad if we just had an "or" there, or would then there be a risk of getting misunderstood as exclusive or, as in "either... or" (⊕ in logic, or ^ in C, bitwise)? Whatever, here are my thoughts as an observer; you decide, maybe and/or, to make sure that it gets understood as inclusive or...

Hmm. The thing about "or" is that some readers might misinterpret it as "or, in other words". I'm not sure which is the greater risk. Melchoir (talk) 21:27, 2 February 2014 (UTC)

argumentative

This word has been used for the reasoning of the latest edit: https://en.wikipedia.org/w/index.php?title=1_%2B_2_%2B_3_%2B_4_%2B_%E2%8B%AF&diff=593759534&oldid=593726973

In which sense "argumentative", could I have an elaboration for the reason?

Absolutely, and thanks for asking! (I meant to elaborate on the talk page, but I was distracted...)

I've seen elsewhere on the Internet that there are plenty of debates over heuristic derivations. The debates tend to center around whether or not the derivations are meaningful, and whether it is wise to let impressionable young mathematicians see them. These are subjective value judgements. I have my own opinion, as does everyone else. What we cannot do on Wikipedia is enforce an opinion on others. The change I reverted used the phrases "one has to keep in mind ... cannot be used as a definition ... has to be seen ..." (emphasis in the original). Such language is inappropriate for an encyclopedia.

Generally, we should follow the principles of the policy Wikipedia:Neutral point of view. This is an easy requirement to follow in mathematics, since there are usually precise formulations for any point of view that one might wish to represent. The more precise the language, the less we risk pushing a POV. For example:

• Bad: This derivation is acceptable. Good: The derivation is given in Ramanujan's notebook.
• Bad: This derivation is unacceptable. Good: The derivation is the less rigorous of his two arguments.
• Bad: Step 1 is not justified. Good: Step 1 belongs to a family of transformations that are not always valid, and it is not justified by inclusion in this family alone.

In each example, the Bad and the Good sentence express the same sentiment. The Bad version is a bare value judgement, which is debatable. The Good version is a more objective version that should be uncontroversial.

Incidentally, I also object to the merits of the edit that I reverted. Its mathematical content was the statement that the Dirichlet series of the zeta function does not converge for the argument -1. Yes, that should be pointed out. The statement belongs in the following section, after the Dirichlet series of the zeta is introduced. And in fact, it's already there. Melchoir (talk) 19:10, 3 February 2014 (UTC)

Secondary Summary > "number of mathematically interesting results"

The second paragraph of the whole article starts with this following sentence:

"Although the series seems at first sight not to have any meaningful value at all, it can be manipulated to yield a number of mathematically interesting results, some of which have applications in other fields such as complex analysis, quantum field theory and string theory."

I want to draw the attention over the part between the first and second comma. Unless I am missing something, there is only one, not a number of, mathematically interesting result; which is the assertion, I must say, that 1 + 2 + 3 ... equals -1/12. That aside, I have the feeling that the adjective interesting is not entirely neutral, encyclopedic, and is redundant, similar to how despised would be.

Suggestion: "[...] it can be manipulated to yield a [[Real number|real]] result, which has [...]" — Preceding unsigned comment added by ThoAppelsin (talk • contribs) 20:34, 3 February 2014 (UTC)

Unfortunately, the author of that passage doesn't seem to be active anymore: 80.168.225.18. So they probably won't be commenting here...

I think by "result" they meant "a mathematical statement", not "a number which is the output of an algorithm". So, the fact that zeta function regularization gives you −1/12 is one result. The fact that Ramanujan summation gives you −1/12 is a second result. These two results are related, but they're not the same.

That said, the choice of words isn't perfect, especially "interesting". We already have citations supporting "famous" and "remarkable", so yes, it's redundant. The sentence is pretty vague in general. And does complex analysis really belong in the category of "other fields" when we're talking about divergent series? Melchoir (talk) 00:51, 4 February 2014 (UTC)

I don't think evaluation of the divergent series ∑n has anything to do with complex analysis, although I possibly may not be knowing what complex analysis really is. It rather is just an overcommitment to desperately assign a value to a divergent series, and just a value, which has been achieved through the exclusion of many other manipulations ending up with many other results that would be possible unless a function with terms that have variable powers, eventually to be set to 1, but disallowing that replacement until the manipulation is done, was introduced, so that truly only a single manipulation could be made. Still an invalid manipulation, but an invalid manipulation undercover, and by being the only single manipulation, despite being invalid, no contradictory result is to be found, thanks to the isolated status of it, thanks to the abettor regularized ζ.

So, yeah, nothing imaginary there, no square root of -1, just a function which accepts complex numbers, but never does in this case. It could very well be a function that is only defined for real numbers. And if this -1/12 does have an appliance in complex analysis, then I would say that the complex analysis fits well in that other category. — manual signature: comment added by ThoAppelsin (talk • contribs) 02:54, 4 February 2014 (UTC)

Minus one twelfth

NOTE: Copy of relevant information from a different page.

Main article: 1 + 2 + 3 + 4 + ⋯ § Popular media

See also: Talk:Infinity § Minus one twelfth, Talk:Natural number § Minus one twelfth, and Talk:Summation § Minus one twelfth

Hi Drbogdan,

You seemed very anxious to know whether it is "true" that $\sum _{n=1}^{\infty }n=-{\frac {1}{12}}$. The talk pages of those articles is not really the appropriate venue for discussing that, but it seems reasonable to drop you a note here.

The problem is that you're trying to ask whether it's "true" before it has been agreed what, if anything, it actually means. In the most usual approach to infinite series, the equation is certainly not true. One would say that $\sum _{n=1}^{\infty }n$ diverges (see divergent series). Or, in the context of measure theory, one could say $\sum _{n=1}^{\infty }n=\infty$.

That said, there are certain interpretations under which the equation is true. I don't agree with the commenters who call it a "fallacy" or "nonsense". But you can't just assert it as "true" out of context, because under the most usual interpretations of the notation, it is definitely not true. --Trovatore (talk) 19:11, 5 February 2014 (UTC)

@Trovatore - Thank you *very* much for your comments above (and at Talk:Infinity#Minus one twelfth) regarding my recent edit:

Copied from the Infinity lead (updated-20140206):

Interestingly, the summation of all natural numbers to infinity is "minus one-twelfth".< ref name="NYT-20140203">Overbye, Dennis (February 3, 2014). "In the End, It All Adds Up to –1/12". New York Times. Retrieved February 3, 2014.</ref>< ref>Sondow, Jonathan Analytic continuation of Riemann's zeta function and values at negative integers via Euler's transformation of series. Proc. Amer. Math. Soc. 120 (1994), no. 2, 421–424.</ref>

$\sum _{n=1}^{\infty }n=-{\frac {1}{12}}$

your comments are *greatly* appreciated - seems the equation may be "true" in some contexts - but not in others (esp. usual interpretations) - Thanks again for your comments - and - Enjoy! :) Drbogdan (talk) 20:02, 5 February 2014 (UTC)

See the page 1 + 2 + 3 + 4 + ⋯ where the sumation is examined in detail.--Salix alba (talk): 16:24, 6 February 2014 (UTC)

@Salix alba - Thank you for your comment - and link - yes, the notion seems well described in the article - also, somewhat related, I made the following userbox (updated to your new link)

$\int \!\,$This user knows that $\sum _{n=1}^{\infty }n=-{\frac {1}{12}}$
(NYT 2014 reference/archive)

thanks again for your comment - and - Enjoy! :) Drbogdan (talk) 17:55, 6 February 2014 (UTC)

Linearity and stability

As far as I can tell, there are two methods that may be called zeta function regularization. If we replace

$\sum _{n=1}^{\infty }a_{n}\to \sum _{n=1}^{\infty }a_{n}^{-s}$

and analytically continue to s = −1, then we get a method that is stable but not linear. If we replace

$\sum _{n=1}^{\infty }a_{n}\to \sum _{n=1}^{\infty }a_{n}\cdot n^{-s}$

and analytically continue to s = 0, then we get a method that is linear but not stable. It would probably be better to call the first method "zeta regularization" and the second method "Dirichlet regularization", but that's just my opinion.

For the purpose of regularizing 1 + 2 + 3 + 4 + ⋯, it doesn't matter which method we choose. We wind up with ζ(−1) either way, so we can afford to be vague. But in general, it can matter, and the difference is hinted at in the Infinite arithmetic series article.

So for the new section "Failure of stable linear summation methods", is it better to say that zeta function is not stable, or that it is not linear? Or should we avoid committing to either statement? It may be easier to focus on cutoff regularization / Ramanujan summation, which is definitely linear but not stable.

...and in the time it took me to write this comment, R.e.b. has already fixed the article. :) Melchoir (talk) 01:46, 7 February 2014 (UTC)

Multiline Equations giving errors

I don't know what the problem is but instead of displaying any of the multiline equations on this page, all I'm seeing is the error "Failed to parse(unknown function '\begin'):" followed by the Latex code in red. Site bug? — Preceding unsigned comment added by 152.106.99.20 (talk) 13:44, 7 February 2014 (UTC)

Yes seem to be a site wide problem see Wikipedia talk:WikiProject Mathematics#Problem with multiline equations and Wikipedia:Village pump (technical)/Archive 123#Math aligned environments failing to parse. If you were logged in you could switch to MathJax rendering which works fine.--Salix alba (talk): 14:49, 7 February 2014 (UTC)

the "smoothed curve"

Not sure what is meant by smoothed curve. I can see that the minimum of the quadratic that fits the points (1,1), (2,3), (3,6), (4,10) etc is -1/12, but that its not the quadratic that is graphed there. I propose that you clarify the meaning of "smoothed curve" in this context. -papasandy

Thanks for the feedback! I'm sure the prose could be improved, but I'm not sure exactly which part you're referring to. There are three diagrams that show a curve, and there is some accompanying text in the "Smoothed asymptotics" section, but the phrase "smoothed curve" isn't used.

By the way, the quadratic that fits the points (1,1), (2,3), (3,6), (4,10), ... directly is x(x+1)/2, which has a y-intercept of 0 and a minimum of −1/8. The catch is that when we promote that sequence to a function of a real variable, the resulting stair-step function is jagged and does not approach a quadratic. The original quadratic x(x+1)/2 only fits the top of the steps; shifting it 1 unit to the right gets us x(x−1)/2, which fits the bottom of the steps. At each extreme, the y-intercept is 0. If we compromise and shift half a unit to the right, we get a y-intercept of −1/8, coinciding with the minimum of the quadratic. If we average over all possible shifts, we get an average y-intercept somewhere between 0 and −1/8, which is, lo and behold, $\int _{0}^{1}{\frac {x(x-1)}{2}}=-{\frac {1}{12}}.$ Anyway, I digress, because that isn't the general definition of the smoothed sum. There might be a connection to the general theory, but I haven't attempted to prove or disprove such a connection, and in any case, I wouldn't add such material to the article without a reference.

Returning to cutoff regularization as described by Tao: After applying a cutoff to the partial sums, we do get a smooth function with a quadratic asymptote, which is −1/12 + CN². The article explains what it means to apply a cutoff. Melchoir (talk) 00:53, 12 February 2014 (UTC)

Interpolation Image is wrong

The Intersecting values of the interpolated curve follow the function y=(x^2)/2, so how can x=0,y=-1/12 ? Unless I am mistaken, can anyone tell me why this is? Or is it part of another function? Because all the summed values follow the function y=(x^2)/2Shroobtimetraveller (talk) 07:22, 12 March 2014 (UTC)

If you're talking about Image:Sum1234Summary.svg, the green curve is y=(x^2)/2 - 1/12.

Meanwhile, the nth partial sum of the original series is (n^2 + n)/2. Melchoir (talk) 08:24, 12 March 2014 (UTC)

The function is in fact y=(x^2)/2 - 1/8. So the intersect is at -0.125 and not at -1/12. — Preceding unsigned comment added by 81.188.107.70 (talk) 11:21, 18 December 2014 (UTC)

A Seemingly Wrong Sentence

Hello, I found in this wikipedia page the following sentence

More generally, ζ(s) will always be given by the degree zero term of the Laurent series expansion around, $h=0$, of, $\sum _{n=1}^{\infty }{n^{-s}}e^{hn}$.

The sentence seems to me wrong. First of all the series, $\sum _{n=1}^{\infty }{n^{-s}}e^{hn}$, is divergent of Re(h)>0, so I have some doubt that it has a Laurent series expansion. Secondly, there is no trace of this expression of the Riemann zeta function in the literature I know. I am not an expert in complex analysis, so I would like someone to confirm my guess. Thank you very much for your attention. Best Regards, Maurizio Barbato PoppiesInAWheatField (talk) 21:18, 18 December 2014 (UTC)

I took the liberty of converting your TEX script into inline-TEX, a bit of a no-no if we were debating, which we are not. I also am not an expert in complex analysis, but know enough to recognize that you might be right about it not having a Laurent series expansion. Let's hope a real expert is watching this page.--guyvan52 (talk) 12:31, 19 December 2014 (UTC)

Thank you very much Guy for having edited my talk. Myabe the editor of the article confused "Laurent series" and "asymptotic expansion". In any case, a reference of this unusual expression of the Riemann zeta-function would be needed, so I took the liberty of remving the statement under dicussion from the article, hoping some expert of the field could enlighten the issue. PoppiesInAWheatField (talk) 13:37, 19 December 2014 (UTC)

The Laurent series/expansions are calculated by integrating around the expansion point, after multiplication by an appropriate power of (z-a). Does that get us something?--guyvan52 (talk) 15:41, 19 December 2014 (UTC)

Dear Guy, the issue is not so trivial to be solved with some obvious observation. As I said, only an expert can confirm or reject the validity of the statement under discussion (in which as I also said, the term "Laurent series" seems to be replaced by "asymptotic expansion". Thank you for your attention.PoppiesInAWheatField (talk) 12:11, 21 December 2014 (UTC)

Failure of stable linear summation methods

Subtracting gives 1 + 1 + 1 + ... = x – x = 0 by linearity

Subtracting of what from what? How did you get this from the original equation? Can you please make this step more descriptive? — Preceding unsigned comment added by Griii2 (talk • contribs) 12:24, 20 January 2015 (UTC)

Is it clearer now? --JBL (talk) 23:12, 20 January 2015 (UTC)

Does numberphile's term-by-term summation method render on all browsers?

I tried to remember numberphile's Youtube term-by-term method and failed. It didn't show up on the top Google searches, and I really didn't want to watch the video for the 20th time. I assume I am not unique here (especially in forgetting the calculation) so after getting it straight I posted it here. It takes up two or three lines because I used collapsible text. My only concern is this: Does it render properly on all browsers?--Guy vandegrift (talk) 00:15, 19 June 2015 (UTC)

Funny, but wrong

In order for Wikipedia to remain trustworthy, I suggest adding a disclaimer to the head of the article. In my oppinon, the given "proofs" are quite funny, so I'd rather keep the article.

In case you doubt the erroneousness of the proofs, let's just address the "Heuristics". Using the same argument, I get a different result for -3c:

${\begin{alignedat}{8}c&{}={}&1&+2&&{}+3+4&&{}+5+6+\cdots \\4c&{}={}&4&+8&&{}+12+16&&{}+20+24+\cdots \\-3c&{}={}&-3&-6&&{}+-9-12&&{}-15-18+\cdots \\\end{alignedat}}$

Which illustrates that this kind of addition is just plain wrong. If you wanted to compute the sum correctly, you'd have to consider the limit of partial sums and obey the corresponding mathematical rules. In particular, swapping limit and sum has never been allowed for diverging series.

Considering section "Zeta function regularization": This section actually explains why its proof does not work: "When the real part of s is greater than 1...", afterwards s is set to 1. This problem has not been addressed -- and neither has the usage of the argument of section "Heuristics" (disguised using the magic exponent "-s").

I have not analyzed the remaining sections, but as long as the definition of 1+2+3+4... is not changed to something other than the ordinary sum of natural numbers, these proofs can only be wrong, too.

By the way, what's the supposed meaning of the image stating "The parabola is their smoothed asymptote; its y-intercept is −1/12."? The only parabola which comes to my mind is the common formula for the partial sum, i.e. $\sum _{k=1}^{n}k={\frac {n(n+1)}{2}}={\frac {1}{2}}n^{2}+{\frac {1}{2}},$ which intercepts the y-axis at 0. — Preceding unsigned comment added by 93.190.250.130 (talk) 14:26, 26 February 2015 (UTC)

As is often the case in mathematics, it all depends on which rules you are playing to. With the rules of conventional limits ("standard analysis") then the infinite series is divergent and does not have a sum - this is pointed out in the introduction. However, there are various "non-standard" approaches which can be used to assign meaningful sums to series like this one - more information is given in our divergent series article. Some of the derivations in this article are not rigorous - that is also noted in the artcile itself. But it takes a brave man to argue that mathematicians such as Hardy and Ramanujan are just "wrong". Gandalf61 (talk) 17:23, 26 February 2015 (UTC)

To address 93.190.250.130's questions individually...

The section "Heuristics" contains heuristics, not proofs.

The section "Zeta function regularization" describes the need for analytic continuation. There is no magic; every individual claim is true at face value. By the way, s is set to -1, not 1.

The ordinary sum of natural numbers is treated in the first section, "Partial sums", which explains that it diverges. The entire purpose of the following "Summability" section is to explore other definitions.

The image of the parabola is part of the "Cutoff regularization" section. It illustrates the result of cutoff regularization, which is described in the text. Melchoir (talk) 19:25, 26 February 2015 (UTC)

I must say, the next-to-last comment above — "As is often the case in mathematics . . . But it takes a brave man to argue that mathematicians such as Hardy and Ramanujan are just 'wrong'" — is utter, complete, total nonsense. Fortunately, the article is — as of now — very clear about what means what. And by the way, Ramanujan was not formally schooled in modern mathematical notation, which especially nowadays has a precise meaning. Mathematicians don't use incorrect notation when they can help it. Instead, they explain what means what, which is just what the article now does. (And many thanks to whomever fixed it.)Daqu (talk) 22:15, 18 September 2015 (UTC)

Totally wrong illustration

The illustration of the graph of the Riemann zeta function on the real numbers, with caption:

"Plot of ζ(s). For s > 1, the series converges and ζ(s) > 1. Analytic continuation around the pole at s = 1 leads to a region of negative values, including ζ(−1) = −1/12"

is totally wrong and should be replaced as soon as possible by a correct graph.Daqu (talk) 18:54, 9 September 2015 (UTC)

It looks okay to me. Why do you think it's wrong? --JBL (talk) 20:59, 9 September 2015 (UTC)

I was wrong — it's not technically wrong. But it gives a totally wrong impression of zeta on the negative numbers: It makes zeta(s) appear as if it is asymptotic to 0 as s → -oo.

But for example, the image of zeta applied to the closed interval [-100.5, -99.5] contains the closed interval [-1.0 × 10⁷⁸, +7.0 × 10⁷⁶].Daqu (talk) 22:03, 18 September 2015 (UTC)

Yes, I see your point. I offer two (unfortunately non-constructive) comments:

• This is not an article about the zeta function, so I don't really see that this matters very much; someone who wants to learn about the zeta function should not be at this article.
• It is nice to have a figure, so perhaps the best solution would be a modified version of this figure with a smaller range on the axes (say, [-2, 2]^2 or something) to avoid the long flat part. Whoever edits the image (and this comment is non-constructive because said person is not going to be me) could also put in a point marking the relevant value zeta(-1).

--JBL (talk) 22:59, 18 September 2015 (UTC)

The statement that "someone who wants to learn about the zeta function should not be at this article" indicates a complete lack of understanding of the purpose of an encyclopedia. An encyclopedia is supposed to provide correct information, not incorrect information.Daqu (talk) 16:00, 28 September 2015 (UTC)

Thanks for that polite and constructive contribution. --JBL (talk) 16:13, 28 September 2015 (UTC)

0 + 2 + 0 + 4 + ... is Ramanujan summable?

Regarding this recent edit with the summary "Deleted wrong statement since there is a simple proof that 0 + 2 + 0 + 4 + ... is Ramanujan summable to -1/6."... Are you referring to a different definition of Ramanujan summability than Hardy's? Perhaps it would be clearer to give the proof here on the talk page, so we can see what it means. Melchoir (talk) 19:28, 16 December 2015 (UTC)

---

Thank you for the opportunity to reply. The heuristic argument in the article corresponds to a formal definition. For $f(x)=\sum _{n=0}^{\infty }a_{n}x^{n}$, a real number $R,R\neq 1$, and $g(x)=f(x)-Rf(x^{2})$, if the series $g(1)$ is Abel summable, $f(1)$ is Ramanujan summable to ${\frac {g(1)}{1-R}}$.

The result follows from the fact that $\lim _{x\to 1^{-}}g(x^{2})=g(1)$ for $f(x)={\frac {x}{(1-x)^{2}}}$ and $g(x)={\frac {x}{(1+x)^{2}}}$, with $R=4$. — Preceding unsigned comment added by 2804:14c:8780:a082:8096:8a62:5204:6fba (talk • contribs) 17:06, 17 December 2015‎

But the heuristic argument in the article is not claimed as a definition. The article should follow the definition of Ramanujan summability in Hardy and in Berndt. Melchoir (talk) 22:35, 17 December 2015 (UTC)

---

Anyway, the statement "such a series must be interpreted by zeta function regularization" is false, isn't it? — Preceding unsigned comment added by 2804:14C:8780:A082:8096:8A62:5204:6FBA (talk) 23:17, 17 December 2015 (UTC)

Ah yes, "must" should read "may be" there. Melchoir (talk) 00:40, 18 December 2015 (UTC)

---

The above defined elementary Ramanujan sum implies that $1-1+2-2+3-3+\cdots forstudy=1/8$. Is it Ramanujan summable according to Hardy's definition? — Preceding unsigned comment added by 2804:14C:8780:A082:F059:3DBC:75AE:EA88 (talk) 20:05, 23 December 2015 (UTC)

---

A related comment on the motivation for study in the article at https://en.wikipedia.org/wiki/Divergent_geometric_series

For all complex number $R\neq 1$, $f_{R}(x)=x+Rx^{2}+R^{2}x^{4}+R^{3}x^{8}+\cdots$ is elementary Ramanujan summable to ${\frac {1}{1-R}}$, since $f_{R}(x)-Rf_{R}(x^{2})=x$.

According to that motivation, the Borel-Okada principle implies that $F_{R}(x)=a_{0}x+a_{1}Rx^{2}+a_{2}R^{2}x^{4}+a_{3}R^{3}x^{8}+\cdots$ is elementary Ramanujan summable to the analytic continuation of $F_{R}(1)$.

"Failure of stable linear summation methods" section inadequate

This section includes the following:

   0 +1 + 2 + ... = 0 + x = x by stability

Subtracting gives

   1 + 1 + 1 + ... = x – x = 0 by linearity 

This is wrong. What has been done here is that the two sequences have been subtracted term by term. This assumes some sort of term alignment, which is not possible with infinite series (see the explanation of 1+2+3+... = -1/12 further up the page).

The only acceptable description of 0+1+2+... -x is (0+1+2+...)-(1+2+3+...) or (-1/12)-(-1/12) or 0

If we start aligning terms arbitrarily, we need to remove the explanation of x=-1/12 — Preceding unsigned comment added by 81.147.10.55 (talk) 15:51, 21 April 2014 (UTC)

That's the whole point of the section, showing we can't do everything with infinite series. This is clearly stated, please do not remove the sectionKlinfran (talk) 13:25, 23 May 2016 (UTC)

Requested move 28 May 2016

The following is a closed discussion of a requested move. Please do not modify it. Subsequent comments should be made in a new section on the talk page. Editors desiring to contest the closing decision should consider a move review. No further edits should be made to this section.

The result of the move request was: Not moved as consensus to keep the article at it's current name has been established. (closed by non-admin page mover) — Music1201 ^talk 01:26, 12 June 2016 (UTC)

---

1 + 2 + 3 + 4 + ⋯ → Sum of the Natural Numbers – I think that my proposed title is more "technically" correct, because to me it seems that there could be confusion as to how long we will perform the addition for. Sum of the Natural Numbers implies that the addition will go on for all such numbers, not stop at a particular point. Thanks for considering this. Gluons12 (talk) 15:42, 28 May 2016 (UTC) — relisted by user:SSTflyer at 09:42, 5 June 2016 (UTC)

• Support Sum of the natural numbers. I see no reason to title-case this, but otherwise this is a good proposal.  ONR  (talk)  20:09, 29 May 2016 (UTC)
  • No opinion, but if the article is to be moved, it should be moved to Sum of the natural numbers per ONR. HandsomeFella (talk) 19:34, 30 May 2016 (UTC)
• Oppose The notation 1 + 2 + 3 + 4 + ⋯ is actually used in the cited scientific references, whereas "sum of the natural numbers" is only used in blogs referring to the Numberphile video. This is because "sum of the natural numbers" is meaningless -- there is no such sum. This article is about a certain formal series, which is divergent. The only time it makes sense to refer to a series as a "sum" of the set of its terms is when the series is not only convergent, but absolutely convergent, so that the order doesn't matter. There's another problem that "the natural numbers" is ambiguous: sometimes that includes 0 (number theory), and sometimes it doesn't (set theory). This is a problem because the series 0 + 1 + 2 + 3 + ⋯ is a different formal series than 1 + 2 + 3 + 4 + ⋯, and the two series have different Ramanujan sums. So if you really want a "technically correct" title, it would be "series of the natural numbers in order starting from 1". But that's really overkill. If you're worried about explaining that the series is infinite, the correct place to do so in within the text of the article. Melchoir (talk) 01:06, 30 May 2016 (UTC)
• Oppose per Melchoir. --JBL (talk) 14:59, 5 June 2016 (UTC)
• Oppose per Melchoir. Gap9551 (talk) 20:07, 5 June 2016 (UTC)
• Oppose per Melchoir.--John123521 (Talk-Contib.) RA 01:01, 8 June 2016 (UTC)

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The above discussion is preserved as an archive of a requested move. Please do not modify it. Subsequent comments should be made in a new section on this talk page or in a move review. No further edits should be made to this section.

auto archive?

I see discussions sections that are ten years old. Anyone have an objection to auto-archiving this talk page? Mr. Swordfish (talk) 16:43, 25 January 2017 (UTC)

Not I. JBL (talk) 21:51, 25 January 2017 (UTC)

Making more clear the left hand side is not a series

I strongly disagree with this revert by Melchoir: while I agree that that sentence was a slight repetition, I think it is still important to make completely clear that 1 + 2 + 3 + 4 + ⋯ does not have its usual meaning. At the moment in the first paragraph this is not openly written as it is only stated that the most common summation methods would not work because the series diverges but other methods would, definitely confusing people with a very limited knowledge about the topic. I think the initial section of this page should absolutely make clear to everybody that: 1) the series diverges, 2) when interpreting the left hand side not as a series in the usual meaning but in a suitable sense the expression is equal to -1/12. At the moment this is made clear only to people who already have some good familiarity with series, and this is a pity because it would be possible to make it clear to everybody.--Sandrobt (talk) 09:43, 25 January 2017 (UTC)

I had thought your edit was an improvement, for the reasons you mention. (Maybe the wording of the whole paragraph can be further refined, too.) --JBL (talk) 13:37, 25 January 2017 (UTC)

Agree that it was an improvement and with the reasoning. We should be absolutely clear that 1 + 2 + 3 + 4 + ⋯ does not have its usual meaning. Mr. Swordfish (talk) 16:42, 25 January 2017 (UTC)

Well, as I wrote in my edit summary, my main problem with the edit is that the language is redundant. It's awkward to write "A is written as B, which has to be interpreted as A". I also disagree with the framing of the problem. The notation "1 + 2 + 3 + 4 + ⋯" does represent a series. That series diverges, i.e. has no sum, and that's what the first paragraph says.

Now, I'm sure there's room for improvement of the wording. In fact, the whole lead section should be expanded to better summarize the body of the article. I suspect that giving the prose more room to breathe might make it easier to compromise on the placement of the caveats. (I think there are enough caveats already, but at least this would be a productive way forward.) Melchoir (talk) 20:40, 25 January 2017 (UTC)

I'm OK with improving the wording of the lead section, as long as possible future great improvements don't stop more immediate improvements. Also, it doesn't seem to me that your A-B sentence is really a fair reduction of what I wrote. I agree with you that the notation "1 + 2 + 3 + 4 + ⋯" does represent a series, the point is that typically it does not represent the zeta-function regularization/Ramanujan summation of a series, thus when it is used with this meaning it has to be made absolutely clear what we are talking about. I think that currently it isn't to people without a somewhat good knowledge of the topic and I also think this is not something out of reach, can we agree on this? Btw, notice that the wiki articles of these two summation methods never use just the symbol = alone: the first uses → instead of =, the second adds a $(\Re )$.--Sandrobt (talk) 23:02, 25 January 2017 (UTC)

Since the discussion has cooled off and given the mild consensus above, I've just reverted back to my version. @Melchoir, I'd be happy if you improve the style and the clarity of the introduction with a more general rewording, but please make sure it remains very clear to every reader that 1 + 2 + 3 + 4 + ⋯ does not have its usual meaning.--Sandrobt (talk) 22:25, 1 February 2017 (UTC)

Roger that! I'll get around to it someday™. Melchoir (talk) 01:15, 2 February 2017 (UTC)

An easy to understand explanation

If someone wanted, they could transcribe the proof presented here: https://www.youtube.com/watch?v=w-I6XTVZXww&feature=youtu.be

Basically, if

S_1=1-1+1-1+1-1+...=1/2,
then
S_2=1-2+3-4+5-6+...=1/4
and
if S=1+2+3+4+5+6+...
then
S-S_2=4+8+12+...=4*S
and so
3S=-S_2=-1/4
and S=-1/12
— Preceding unsigned comment added by 85.76.117.165 (talk) 14:14, 10 January 2014 (UTC)

to clarify. already the first step $S_{1}=1-1+1-1+1-1+...=1/2$ is wrong. the sequence of partial sums of this series alternates between 0 and 1. so the series of partial sums is (1,0,1,0,1,0, ..) and it doesn't converge (doesn't have a limit). then if you ASSUMED (the WRONG thing) that S_1 actually exists/converges, the next steps would be correct. however, no result follows from this, in the same way that you can conclude anything you want from the false equation "1 = 0". it troubles me that some guy does those videos on youtube, and has obviously no knowledge of the most basic mathematics (university level this is week 3 of a 5 years), but expresses those false things with the authority of some postdoc and doesn't scrutinize his own results, when the FIRST line of this article says the series is DIVERGENT. then in the end "yeah this is an odd result, but then i guess many physics results are counterintuitive, so this can, after all, be correct". sorry, this is no justification, this is not a mathematical approach and no physicist will say that this sum is really -1/12 (i am one). the series is divergent and will remain divergent until the end of time, the -1/12 is not totally incorrect but one has to be very careful in the wording, what's certainly false is that "the series of natural numbers converges to -1/12".

please be responsible and do correct mathematics when you do youtube videos or if you sum in a "non-standard way" then you need to explain this "generalized meaning" of "summation". (simmilarly when we talk of functions with lebesgue integrals, when we are really talking about equivalence classes of functions. we just say functions but it's not correct, we have to be more specific outside of this context.)

92.196.5.246 (talk) 14:07, 17 January 2014 (UTC)

The statement $S_{1}=1/2$ is not necessarily false. A way of showing this that occurred to me is to say $1-S_{1}=1-(1-1+1-1+1-...)=1-1+1-1+...=S_{1}$. From here we say $1-S_{1}=S_{1}$. We add $S_{1}$ to both sides and find $1=2S_{1}$. Then, dividing by two will show $S_{1}=1/2$. Of course, this is assuming that $S_{1}$ can be treated as a number that we can use in algebra. Gluons12 (talk) 15:32, 28 May 2016 (UTC).

How about if I add up the 1st and 3rd terms, the 2nd and 4th terms, etc., I would have $S_{1}=2-2+2-2+2-...=1$. In fact, I could add up the first k positive terms, the first k negative terms, etc., I would have $S_{1}=k-k+k-k+k-...=k/2$, where k=1, 2, ..., infinity. --Roland (talk) 05:37, 2 February 2017 (UTC)

Easy to understand is good, but easy doesn't mean correct. and if it's wrong, there's nothing to understand, because when there's no logic behind the result what's there to understand? the calculation is kind of random. the limit of 1 - 1 + 1 - 1 + .. is taking to have an arbitrary value (1/2). any other value could have been chosen with the same reasoning (why the arithmetic average not the geometric average which would be 0) and the result would have been different. 92.196.5.246 (talk) 14:10, 17 January 2014 (UTC)

That's too pessimistic. The intuitive manipulations may appear random at first, but they aren't. It should be possible to relate the intuitive manipulations to manipulations of formal Dirichlet series that converge on some common open set, ultimately mirroring a proof that zeta(-1)=-1/12 by comparing with the Dirichlet series of the eta function, where eta(0)=1/2 is not at all arbitrary. Melchoir (talk) 20:46, 17 January 2014 (UTC)

This is whats done in the response to comments on the numberphile video[4]. Three complex series are defied

$S_{1}(z)=1+\sum _{n=1}^{\infty }(-1)^{n}\left[(n+1)^{-z}-n^{-z}\right]$

$S_{2}(z)=\sum _{n=1}^{\infty }(-1)^{n+1}n^{-z}$

$S(z)=\sum _{n=1}^{\infty }n^{-z}$

Substituting $z=-1$ gives the series $S_{1}$, $S_{2}$ and $S$ above. It can be shown

$S(z)-S_{2}(z)=2^{1-z}S(z)$ putting $z=-1$ gives $S-S_{2}=4S$ and ultimately $S=-1/12$.--Salix alba (talk): 07:58, 27 January 2014 (UTC)

I've gone ahead and added a slightly different version of the simple explanation, including the crucial step of multiplying by 4. This argument was given by Ramanujan, and that alone should justify repeating it, if only for historical commentary! Melchoir (talk) 05:49, 27 January 2014 (UTC)