Talk:Analyticity of holomorphic functions

Circular logic[edit]

From this article:

Suppose f is differentiable everywhere within some open disk centered at a. Let z be within that open disk. Let C be a positively oriented (i.e., counterclockwise) circle centered at a, lying within that open disk but farther from a than z is. Then, using Cauchy's integral formula, we get...

From Cauchy's integral formula:

The proof of this statement uses the Cauchy integral theorem and, just like that theorem, only needs that f is complex differentiable. One can then deduce from the formula that f must actually be infinitely often continuously differentiable, with

f^{(n)}(a)={n! \over 2\pi i}\oint _{C}{f(z) \over (z-a)^{n+1}}\,dz.

Some call this identity Cauchy's differentiation formula. A proof of this last identity is a by-product of the proof that holomorphic functions are analytic.

So:

To prove that holomorphic functions are analytic, we need
The Cauchy integral formula, but to prove that we need
The fact that $f^{(n)}(a)={n! \over 2\pi i}\oint _{C}{f(z) \over (z-a)^{n+1}}\,dz$ , which is a byproduct of the proof that
Holomorphic functions are analytic

I encountered this trying to prove to myself that $f^{(n)}(a)={n! \over 2\pi i}\oint _{C}{f(z) \over (z-a)^{n+1}}\,dz$ ; unfortunately, Wikipedia doesn't seem to help because of this circular loop :(.

Or maybe I'm just missing something? Domenic Denicola 01:10, 11 December 2005 (UTC)[reply]

You misread the quote from CIF: "One can then deduce from the formula that f must actually be infinitely often continuously differentiable, etc." So, no circle is involved: you first prove the Cauchy integral theorem, then deduce from it the Cauchy integral formula (as sketched there), and then deduce that holomorphic functions are analytic (as decribed here). -- EJ 00:18, 18 December 2005 (UTC)[reply]

Area of convergence[edit]

The series converges to the correct value on any open disk around a point if that open disk doesn't contain singularities. Can this area be extended (I'm assuming differentiability at all points considered)? E.g. does it follow that the series converges to the correct value everywhere except at singularities? Or is the maximum open disk not containing singularities the biggest area for which such a general statement holds? 82.103.195.147 12:27, 12 August 2006 (UTC)[reply]

The latter. See radius of convergence. -- EJ 15:53, 12 August 2006 (UTC)[reply]

does this really warrent an encylopedia article?[edit]

it seems like it may be more appropriate on Wikibooks (in some math book) or on Wikiversity as some sort of learning module.. --Emesee (talk) 07:33, 22 February 2008 (UTC)[reply]

I'll just add an "I agree" here. The content is good, but it certainly is not encyclopedic in any way. JokeySmurf (talk) 19:26, 16 March 2009 (UTC)[reply]

I disagree. Besides proofs that are notable by themselves (which obviously warrant encyclopedia articles), short proofs of notable results are also encyclopedic IMHO. Shreevatsa (talk) 20:23, 16 March 2009 (UTC)[reply]

I also disagree with "Emesee". This is a beautiful argument, central to the subject. I've begun to suspect that people who make comments like "Emesee"'s above think that articles like this are just about technicalities. Non-mathematicians can be REALLY weird in their misperceptions. Michael Hardy (talk) 20:32, 16 March 2009 (UTC)[reply]

Michael, if you disagree with me then please keep the discussion here and ad-hominem attacks off of my talk page. I am a mathematician and I'm not sure why you would assume otherwise, especially considering you made it clear that you've browsed my user page. If you truly believe that this page deserves an encyclopedic article, then find some external sources to back it up ala in accordance with Wikipedia:Notability. As I said before, I agree that the content of this page is good and should be *somewhere*, but as this page exists right now it is not encyclopedic, it's just a beautiful proof. Should we have a page for a proof of the Cayley-Hamilton theorem? Of course not, we should (and do) include the proof within the main article itself. If there are external sources that give a reason why this proof deserves its own page, then by all means reference them. Otherwise this should be merged or moved, in my opinion. JokeySmurf (talk) 20:58, 16 March 2009 (UTC)[reply]

Maybe we should have a page proving the Cayley-Hamilton theorem. If a proof embodies an interesting idea, then it should be here. If it's just plodding through a computation, then it probably shouldn't. I'm puzzled as to what you consider "notable" in the relevant sense. Michael Hardy (talk) 22:45, 16 March 2009 (UTC)[reply]

What I meant by notable is that WP:NOTE generally implies that the page should be on a topic that is itself covered by independent, external sources. While that is true of this theorem, I don't know of any sources that talk about the proof in its own right, rather than in a "here's the theorem, here's the proof" sort of way. That indicates to me that it's the theorem that's notable, while the proof may mathematically be the important part. With the name change to the article that recently took place though, and considering the intro does include the theorem itself, this page seems fine to me now. JokeySmurf (talk) 01:09, 25 March 2009 (UTC)[reply]

It would be a shame to remove this proof. It is very well written and very detailed, and I found it very useful now that I am studying complex variables in college. Wikipedia often contains theorems and proofs presented with more motivation and detail than found in most books, and it should continue that way. —Preceding unsigned comment added by 188.155.112.114 (talk) 20:08, 17 November 2010 (UTC)[reply]

The name of this article[edit]

Originally this was Proof that holomorphic functions are analytic. Then someone moved it to Holomorphic functions are analytic. Then it got moved to Analytic nature of holomorphic functions. Then it was moved back to its original title.

Does anyone have any preferences or arguments for them? (I think I'm going to delete the first two words again.) Michael Hardy (talk) 21:34, 24 March 2009 (UTC)[reply]

I too prefer not having "Proof of" in the title (since the article is about more than the proof). At the same time, it is somewhat unconventional to have the article title be a sentence instead of a noun phrase, but if we can't think of any good alternatives ("Analytic nature of holomorphic functions" is not a good alternative), I guess "Holomorphic functions are analytic" is as good as it gets. Shreevatsa (talk) 22:03, 24 March 2009 (UTC)[reply]

Requested move[edit]

The following discussion is an archived discussion of a requested move. Please do not modify it. Subsequent comments should be made in a new section on the talk page. No further edits should be made to this section.

The result of the move request was: Move. Jafeluv (talk) 13:35, 13 January 2010 (UTC)[reply]

Holomorphic functions are analytic → Analyticity of holomorphic functions — I find it strange having a full sentence as the name of an article.—216.239.65.88 (talk) 13:19, 6 January 2010 (UTC)[reply]

Support - per our naming conventions, article titles are supposed to be nouns, not sentences. Parsecboy (talk) 21:03, 7 January 2010 (UTC)[reply]
Support per above. --Salix (talk): 21:45, 7 January 2010 (UTC)[reply]

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. No further edits should be made to this section.

(Of course originally the title of this article was a noun; it's been moved at least twice.) Michael Hardy (talk) 03:04, 14 January 2010 (UTC)[reply]

The notation "[["

The article starts, "In complex analysis,...a complex-valued function ƒ of a complex variable z: [[". Not being a mathematician, I don't understand the notation "[[". Can this be rewritten in some form that makes sense to people who are not specialists? I am used to seeing phrases like "function f of a complex variable z: f(z), where z=x+iy", which I understand. David Spector (talk) 18:45, 3 January 2012 (UTC)[reply]

Add a list of theorems about holomorphic functions[edit]

Just like the bottom of the Twin prime lists prime number classes, this article should give a list of theorems about holomorphic functions because otherwise it's really hard to find a Wikipedia article about another theorem about holomorphic functions if you don't know the name of that theorem. For example, there might be a very hard to find article about the following statements that I don't know if are true or if have been proven: that all bijective functions that are holomorphic on C are linear, and that for all holomorphic functions f on a closed disk, there exists functions g and h that are holomorphic on C such that for any complex number x in that disk, you can get f(x) by applying the inverse of the part of the function g restricted to the image of the closed disk then applying h. The theorem that all holomorphic functions on an open disc are analytic in that disc, that I could find an article on should also be in the list of theorems about holomorphic functions. Was a WikiProject the method of gathering articles to add to the list of prime number classes? Blackbombchu (talk) 20:33, 5 April 2014 (UTC)[reply]

Who proved this theorem?[edit]

Or, more generally, what is the history of this theorem? Could someone please add this information to the article? — Preceding unsigned comment added by 62.80.108.37 (talk) 09:48, 31 October 2019 (UTC)[reply]