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Finding the real and imaginary parts of a function

shen07

Member
Aug 14, 2013
54
If f:C-->C is holomorphic and CodeCogsEqn.gif , find the real and imaginary parts ug and vg of g in terms of the real and imaginary parts uf and vf of f.
 

ZaidAlyafey

Well-known member
MHB Math Helper
Jan 17, 2013
1,667
Re: Please can you give me some hint to do this exercise

For clarification you mean by \(\displaystyle u_g=\text{Re}(g) \) and \(\displaystyle v_g=\text{Im}(g)\) using that \(\displaystyle g(x,y) = u(x,y)+iv(x,y)\) , right?
 

shen07

Member
Aug 14, 2013
54
Re: Please can you give me some hint to do this exercise

For clarification you mean by \(\displaystyle u_g=\text{Re}(g) \) and \(\displaystyle v_g=\text{Im}(g)\) using that \(\displaystyle g(x,y) = u(x,y)+iv(x,y)\) , right?
yeas right
 

ZaidAlyafey

Well-known member
MHB Math Helper
Jan 17, 2013
1,667
Re: Please can you give me some hint to do this exercise

I would suggest starting by

\(\displaystyle u_f = \frac{f(z)+\overline{f(z)}}{2}\)
 

shen07

Member
Aug 14, 2013
54
Re: Please can you give me some hint to do this exercise

I would suggest starting by

\(\displaystyle u_f = \frac{f(z)+\overline{f(z)}}{2}\)

One more question what is \(\displaystyle \overline{f(\overline{z})}\) actually?? i dont quite understand this!
 

topsquark

Well-known member
MHB Math Helper
Aug 30, 2012
1,123
Re: Please can you give me some hint to do this exercise

One more question what is \(\displaystyle \overline{f(\overline{z})}\) actually?? i dont quite understand this!
Consider a simple example:
[tex]f(z) = u(z) + i v(z)[/tex] with z = x + iy.

Then
[tex]f(z) = u(x + iy) + i v(x + iy)[/tex]

[tex]f( \overline{z} ) = u(x - iy) + i v(x - iy)[/tex]

[tex]\overline{f( \overline{z} ) } = u(x - iy) - i v(x - iy)[/tex]

Is this what you are looking for? Or something more conceptual?

-Dan
 
Last edited:

Fernando Revilla

Well-known member
MHB Math Helper
Jan 29, 2012
661
Another example:
$$f(z)=z^2+i \Rightarrow \overline{f\left({\bar{z}}\right)}=\overline{(\bar{z})^2+i}=\overline{ \overline{z^2}+i}=\overline{\overline{z^2}}+\bar{i}=z^2-i$$