Talk:Weierstrass factorization theorem

Typos

Hi! there are typos: it should be as follows

Then there exists an entire function that has (only) zeroes at every point of {zi}; in particular, P is such a function1:

   P(z)=\prod_{i=1}^\infty E_{p_i}\left(\frac{z}{z_i}\right).

I doubt that this statement is correct:

 *
         The theorem may be generalized  ..... respectively;

then: f(z)=\frac{\prod_i(z-z_i)}{\prod_j(z-p_j)}.

Why should any of these products converge?

cu , F

Clean-up needed

Article says:

Holomorphic functions can be factored: If f is a function holomorphic in a region,

\Omega

, with zeroes at every point of

\lbrace z_{i}\rbrace _{i}\subset \mathbb {C} -\{0\}

then there exists an entire function g, and a sequence…

What is $\Omega$ ? Simply connected? Are the zeroes in $\Omega$ ? (where else!) Are they simple zeroes or multiple? I really doubt that the statement, has it stands now, is correct. Everything would be fine if $\Omega =\mathbf {C}$ and if the zeroes allow multiplicity, but I don't know what the editor really meant. --Bdmy (talk) 18:37, 10 April 2009 (UTC)[reply]

Cosine formula

Is the cosine formula correct? I only ask because it goes to zero when z=0. Psalm 119:105 (talk) 11:12, 20 August 2009 (UTC)[reply]

You're right, there was a mistake in the formula. I removed the \pi z factors. - Greg

Examples of factorization

In the right hand of both examples there are exponentials lacking.

It would be nice to give an example when the entire function does not have any zero (some exponential). —Preceding unsigned comment added by 163.10.1.186 (talk) 17:41, 21 October 2009 (UTC)[reply]

These factorisations are correct. The intermediate expression is the Weierstrass factorisation, which can be obtained for example by expressing sin and cos using gamma functions. The RHS can be found in, for example, Gradshteyn/Ryzhik 1.431. 138.38.106.191 (talk) 11:35, 22 January 2013 (UTC)[reply]

First sentence of the Motivation

The fact that every finite sequence of complex numbers is the set of zeros of some polynomial function is true, but not a consequence of the Fundamental of Algebra. Proof is that that claim is true for real numbers, and actually for any field. — Preceding unsigned comment added by 175.223.31.17 (talk) 10:10, 14 June 2019 (UTC)[reply]

Recognition of brilliance

There is something striking about the formal statement of the theorem. It is the entirety of the subsection "The Weierstrass factorization theorem," which ought to be important to this article. I have zero complaints about nothing regarding none of the null characteristics of this non-explanation. Nothing isn't empty in the vacuousness of its zeroness:

Let $ƒ$ be an entire function, and let $\{a_{n}\}$ be the non-zero zeros of $ƒ$ repeated according to multiplicity; suppose also that $ƒ$ has a zero at $z = 0$ of order $m \geq 0$ (a zero of order $m = 0$ at $z = 0$ is taken to mean $ƒ (0) \neq 0$ —that is, $f$ does not have a zero at $0$ )...

OK, but in seriousness, surely there is a less confusing way to describe this. While I actually find the paragraph about zeroes somewhat enchanting, it clearly does not help with understanding the theorem. Eebster the Great (talk) 05:11, 4 June 2023 (UTC)[reply]

Two possibilities in the direction of the concern raised are:

1) To omit the m=0 condition entirely. I personally do not prefer this nor is it recommended because there is a loss of factual information in this simplification.

2) To keep m>=0 but to move the explanation of the m=0 meaning to a (foot/end) note.

Personally, I do not think there is anything wrong with it as is. But if clarifying was of paramount importance then I would opt for possibility 2) above. I encourage you to make the (foot/end) note, moving the m=0 explanation out of the theorem, as it is not of immediate importance. This type of rearrangment of information is completely reasonable and routine. MMmpds (talk) 21:47, 4 June 2023 (UTC)[reply]

The definition of a zero of order 0 is consistent, but it is also confusing. For instance, it implies that every point in the domain of every function is a zero (of order at least 0). My main complaint though is that in a single sentence, this article uses the word "zero" or symbol "0" twelve separate times, with two different meanings. It has to be some sort of record. The definition should be expanded or clarified, the footnote should be separated out, and alternatives to using the word "zero" over and over should be found if possible. Anyone who doesn't already understand this theorem is not going to be happy with your non-zero zeroes of order zero. Eebster the Great (talk) 21:06, 7 July 2023 (UTC)[reply]

I've moved it into a footnote. (It was changed in this edit from something more sensible; I would not object to restoring the previous version, instead.) --JBL (talk) 21:26, 7 July 2023 (UTC)[reply]

Dang, there was an edit conflict. I was in the middle of making this suggestion:

Let

ƒ

be an entire function, and let

\{a_{n}\}

be an enumeration of the zeros of

ƒ

excluding the origin, repeated according to multiplicity. If

ƒ

(0) = 0, then let

m

represent the multiplicity of that zero. Otherwise, let

m

= 0. Eebster the Great (talk) 21:31, 7 July 2023 (UTC)[reply]

I should say that I read the statement the same as Eebster the Great had re-stated it, which is rather helpful. I only ever took the statement to apply to the origin. Specifically not every point in the domain, unless the domain contained the origin. In which case, if $f(0)\neq 0$ , then $m$ can at most be equal to zero (simultaneously at least) since $m$ must vanish by this definition uniquely.