Accumulation point unit disc

In summary, we have a Weierstrass Product, f(z) = \prod\limits_{n = 1}^{\infty}(1 - nz^n), and we need to prove that every point on the unit circle is an accumulation point of the zeros of f. This can be done by showing that for any z = e^{i\phi} on the unit circle, there exists n and k such that \sqrt[n]{1/n} e^{i2\pi\frac{k}{n}} is close enough to z = e^{i\phi} in both amplitude and phase. By phase, we mean argument. This proof is relatively easy.
  • #1
Dustinsfl
2,281
5
Let [itex]f(z) = \prod\limits_{n = 1}^{\infty}(1 - nz^n) [/itex]

Prove that each point on the unit circle is an accumulation point of zeros of [itex]f [/itex]

So we have that [itex]z = \sqrt[n]{1/n} [/itex]. Now where do I go from here?

Probably should note that this is a Weierstrass Product.
 
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  • #2
The set of all zeros in of f(z) is [itex]\{\sqrt[n]{1/n} e^{i2\pi\frac{k}{n}}|n,k\in Z_+\}[/itex], now for any [itex]z=e^{i\phi}[/itex] on unit circle, there exit n, k such that [itex]\sqrt[n]{1/n} e^{i2\pi\frac{k}{n}}[/itex] is close enough to [itex]z=e^{i\phi}[/itex] in both amplitude and phase ...
 
  • #3
By phase, you mean argument?
 
  • #4
yes, I'm an electrical engineer :)
 
  • #5
sunjin09 said:
yes, I'm an electrical engineer :)

Ok thanks. That problem was relatively easy.
 

1. What is an accumulation point in the unit disc?

An accumulation point in the unit disc is a point that is infinitely close to a sequence of points within the disc. This means that any neighborhood of the point will contain an infinite number of points from the sequence.

2. How is an accumulation point different from a limit point?

An accumulation point is similar to a limit point, but the key difference is that a limit point must have infinitely many points from the sequence in every neighborhood, while an accumulation point only needs to have infinitely many points in at least one neighborhood.

3. Can an accumulation point be located on the boundary of the unit disc?

Yes, an accumulation point can be located on the boundary of the unit disc. This is because the unit disc includes all points within and on the boundary, and an accumulation point can be infinitely close to points on the boundary.

4. How is an accumulation point related to the concept of convergence?

An accumulation point is related to convergence in that if a sequence of points in the unit disc converges, then the limit of the sequence is also an accumulation point. However, not all accumulation points are limits of the sequence, as there can be multiple accumulation points for a single sequence.

5. How can accumulation points be used in mathematical analysis?

Accumulation points are useful in mathematical analysis for understanding the behavior of sequences and their limits. They also have applications in topology and complex analysis, and are used to define important concepts such as compactness and connectedness.

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