Schwarz's lemma, complex analysis proof

Click For Summary
SUMMARY

The discussion centers on applying Schwarz's Lemma to prove that for a holomorphic function f defined on the unit disk B1, with Re f(z) ≥ 0 and f(0) = 1, the inequality |f(z)| ≤ [(1 + |z|)/(1 - |z|)] holds. Participants emphasize the necessity of constructing a mapping function g from the half-plane H to the unit disk, specifically ensuring g(1) = 0. The composition h = g(f) is then analyzed using Schwarz's Lemma to derive the required result, with additional algebraic manipulation to finalize the proof.

PREREQUISITES
  • Understanding of complex analysis concepts, specifically Schwarz's Lemma.
  • Knowledge of holomorphic functions and their properties.
  • Familiarity with mappings between the half-plane and the unit disk.
  • Basic algebraic manipulation skills in the context of complex functions.
NEXT STEPS
  • Study the applications of Schwarz's Lemma in complex analysis proofs.
  • Explore the properties of holomorphic functions in the unit disk.
  • Learn about conformal mappings from the half-plane to the unit disk.
  • Practice algebraic techniques for manipulating complex inequalities.
USEFUL FOR

Students of complex analysis, mathematicians focusing on holomorphic functions, and anyone interested in advanced proof techniques involving Schwarz's Lemma.

QuantumLuck
Messages
19
Reaction score
0

Homework Statement


Let B1 = {z element C : abs(z) < 1}, f be a holomorphic function on B1 with Re f(z) > greater than or equal to 0 and f(0) =1. then show that:

abs(f(z)) less than or equal to [(1+abs(z))/(1-abs(z))]


Homework Equations


Schwarz's Lemma: Suppose that f is analytic in the unit disc, that abs(f) less than or equal to 1 and that f(0) = 0. Then

i. abs(f(z)) less than or equal to abs(z)
ii. abs(f'(0)) less or equal to 1


The Attempt at a Solution


So I know that the solution to this problem involves utilizing Schwarz's lemma (a hint from my professor), however considering the different value of the point at z = 0 is throwing me for a loop. I am not quite sure how to continue from where I am.
 
Physics news on Phys.org
You have f from B1 to H, where H is the half plane {z : Re(z)>0}.

Now create a function g which maps H into the unit disc, such that g(1)=0.

Let h = composition of g and f. Apply Schwarz to h. After that, a little extra algebra is needed to get the desired conclusion.
 

Similar threads

  • · Replies 17 ·
Replies
17
Views
3K
Replies
8
Views
3K
  • · Replies 2 ·
Replies
2
Views
2K
  • · Replies 2 ·
Replies
2
Views
2K
  • · Replies 1 ·
Replies
1
Views
4K
Replies
7
Views
2K
  • · Replies 5 ·
Replies
5
Views
1K
  • · Replies 1 ·
Replies
1
Views
1K
Replies
1
Views
2K
  • · Replies 3 ·
Replies
3
Views
2K