Holomorphic function on the unit disc

In summary, the conversation discusses the existence of a holomorphic function on the unit disc that satisfies a specific condition at certain points. It is concluded that there does not exist a continuous function that meets this criteria and a potential solution involving constructing a new function is mentioned but ultimately deemed unsuccessful. The idea of looking at the zeros of a specific function is suggested as a possible approach to proving the non-existence of such a function.
  • #1
iamqsqsqs
9
0
Does there exist a holomorphic function f(z) on the unit disc and satisfies f(1/n) = f(-1/n) = 1/n^3 for every n in N?
 
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  • #2
There does not even exist a continuous function that does this.
 
  • #3
How can we vigorously prove that? I am thinking of construct a function g such that g(1/n) = g(-1/n) = 1/n^2 and consider f/g to do it. However I am stuck and cannot go on
 
  • #4
What would f(0) be?
 
  • #5
micromass said:
There does not even exist a continuous function that does this.

Last time I checked, [itex]z \mapsto |z|[/itex] was continuous...

iamqsqsqs, try looking at the zeros of f(z) - z^3. Do they form an isolated set of points?
 
  • #6
Citan Uzuki said:
Last time I checked [itex]z \mapsto |z|[/itex] was continuous...


*** Last time I checked [itex]\,\,\displaystyle{\left|\frac{1}{n}\right|\neq \frac{1}{n^3}}[/itex] ...

DonAntonio ***



iamqsqsqs, try looking at the zeros of f(z) - z^3. Do they form an isolated set of points?

...
 
  • #7
Sorry, brain fart. I meant to say [itex]z \mapsto |z|^3[/itex]
 
  • #8
Citan Uzuki said:
Sorry, brain fart. I meant to say [itex]z \mapsto |z|^3[/itex]


Hehe...yes, I supposed so. Happens to me all the time. Your answer to look at the zeroes of [itex]\,\,f(z)-z^3\,\,[/itex] pretty much wraps this up, though.

DonAntonio
 

FAQ: Holomorphic function on the unit disc

1. What is a holomorphic function?

A holomorphic function is a complex-valued function that is differentiable at every point in its domain. It can also be described as a function that is analytic, meaning it can be represented by a convergent power series.

2. What is the unit disc?

The unit disc is the set of all complex numbers with a distance of less than or equal to 1 from the origin on the complex plane. It can be represented by the equation |z| ≤ 1.

3. How is a holomorphic function on the unit disc different from a holomorphic function on the complex plane?

A holomorphic function on the unit disc is a function that is differentiable at every point within the unit disc, whereas a holomorphic function on the complex plane is a function that is differentiable at every point in the entire complex plane. This means that a holomorphic function on the unit disc has a smaller domain of differentiability.

4. Can a holomorphic function on the unit disc have singularities?

Yes, a holomorphic function on the unit disc can have singularities, but only at the boundary of the disc. This is because the unit disc is a compact set, meaning it is closed and bounded, and thus the function must be continuous on its boundary.

5. What is the relationship between holomorphic functions on the unit disc and conformal mapping?

Holomorphic functions on the unit disc are important in the study of conformal mapping, which is a type of transformation that preserves angles. This is because holomorphic functions on the unit disc are also conformal, meaning they preserve angles locally. This property makes them useful in mapping regions of the complex plane to the unit disc and vice versa.

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