Entire Functions Bounded by Exponential Growth

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Homework Help Overview

The problem involves finding all entire functions \( f \) that satisfy the condition \( |f(z)| \leq e^{\textrm{Re}(z)} \) for all \( z \in \mathbb{C} \). This falls under the subject area of complex analysis, particularly focusing on properties of entire functions and growth conditions.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning

Approaches and Questions Raised

  • Participants discuss various approaches, including the application of Nachbin's theorem and the Cauchy integral formula. There is an attempt to utilize the relationship \( |e^z| = e^{\textrm{Re}(z)} \) for simplification. Some participants also explore the Schwarz lemma and question its effectiveness in providing insights about \( f \). The mention of Liouville's theorem suggests a consideration of boundedness in the context of entire functions.

Discussion Status

The discussion is ongoing, with participants exploring different theorems and their applicability to the problem. There is no explicit consensus on a single approach, but several productive lines of reasoning are being examined.

Contextual Notes

Some participants express uncertainty about the effectiveness of certain theorems in yielding useful information about \( f \). The discussion reflects a variety of interpretations and methods being considered without resolving the problem.

Sistine
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Homework Statement


Find all entire functions [tex]f[/tex] such that

[tex]|f(z)|\leq e^{\textrm{Re}(z)}\quad\forall z\in\mathbb{C}[/tex]


Homework Equations


[tex]\textrm{Re}(u+iv)=u[/tex]


The Attempt at a Solution



I tried using Nachbin's theorem for functions of exponential type. I also tried using the Cauchy integral formula to see if I could gain more information about [tex]f[/tex] but I could not solve the problem.
 
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I think you are looking at it in an overly complicated way. Can you think of a way to use |e^z|=e^(Re(z))?
 
I tried applying schwarz lemma to [tex]|f(z)|\leq |e^z|[/tex] i.e.

[tex]\left|\frac{f(z)}{e^z}\right|\leq 1[/tex]

But this did not give me much information about [tex]f[/tex]. What other Theorems from Complex Analysis could I use to gain information about [tex]f[/tex]?
 
Sistine said:
I tried applying schwarz lemma to [tex]|f(z)|\leq |e^z|[/tex] i.e.

[tex]\left|\frac{f(z)}{e^z}\right|\leq 1[/tex]

But this did not give me much information about [tex]f[/tex]. What other Theorems from Complex Analysis could I use to gain information about [tex]f[/tex]?

Liouville's theorem!
 

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