Mapping Between Two DomainsG=(z in bbb C||z|<1,|z+i|>sqrt(2)), S =(z in bbb C|bbb Re(z) in (-pi,pi)}

lollaupligey9

lollaupligey9

Answered question

2022-08-11

Conformal Mapping Between Two Domains (log)
Does anyone have a recommendation as how to go about solving this problem?
I want a conformal from G to H where
G = { z C   |   | z | < 1 , | z + i | > 2 } , S = { z C   |   R e ( z ) ( π , π ) } .
The previous part of the question was to do with branches of the log. Any advice would be most appreciated!
The sort of answer that I'm looking for is this:
Use f(z) = α i log ( z ) + β arg ( z )
then show how to find α and β using the boundaries.
Thanks!

Answer & Explanation

Brogan Navarro

Brogan Navarro

Beginner2022-08-12Added 24 answers

Consider
f ( z ) = 5 π + 8 i Log ( z + 1 z 1 )
The boundary of G consists of two arcs : γ 0 that has the parametrization ϕ ( t ) = e i t for t [ 0 , π ], followed by γ 1 that has the parametrization ψ ( t ) = ( i + ( 1 i ) e i t ) for t [ 0 , π / 2 ]
Now, f ( ϕ ( t ) ) = π + 8 i log ( cot ( t / 2 ) ) and as t varies from 0 to π, the point f ( ϕ ( t ) ) varies on the line x = π from i ( + ) to i ( )
Similarly, f ( ψ ( t ) ) = π 8 i log ( cot ( t / 2 ) 1 2 ) and as t varies from 0 to π / 2, the point f ( ψ ( t ) ) varies on the line x = π from i ( ) to i ( + )
Thus, f ( G ) = S as desired.
polynnxu

polynnxu

Beginner2022-08-13Added 6 answers

G is bounded by two circular arcs, thus it can be mapped by a Möbius transformation to an angular sector A α = { z : 0 < arg z < α }
That angular sector can be mapped to a half-plane or a slit plane by a power function, and finally, the half-plane or slit plane can be mapped to a strip using a logarithm. Scalings and/or rotations at some steps may be helpful.

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