# Conformal mapping with pgfplots

I would like to realize the following graph with pgfplots: which represents the following conformal mapping:

u=x^{1/q}
v=y^{1/q}


where q=2*(pi-alpha)/pi.

EDIT:

Here is the formula for the conformal mapping, as reported in the original article: I really don't know from where should I start to realize a graph of this kind, so every suggestion is welcome. Once I have some useful suggestion, I will try to write my own code.

Thanks for your kind help.

What you want to achieve is a visualization of the complex function f(z) = u(z) + i v(z) with z = x + i y.

In your image, you see two contour plots in the same axis: one for u(z) and one for v(z).

There are only two questions remaining:

1. how can you plot two contour plots of given functions into the same axis, and how can you control their appearance?

2. what are the formulas for u(z) and v(z)?

I can assist you with 1. Concerning 2., I have not been able to reproduce you graph by means of your provided functions. Can you verify them? Are you sure that u(z) = u(x) does not depend on y? And, similarly, that v(z) = v(y) does not depend on x? You image seems to indicate that u and v depend on both x and y. And what is alpha? It seems to be something like pi/5 (that's what I guessed).

So, here is a solution for question (1). Suppose we want to visualize f(z) = z^2 = (x+iy)^2 = (x^2 - y^2) + xy i :

\documentclass{article}

\usepackage{pgfplots}

\begin{document}
\begin{tikzpicture}
\begin{axis}[
view={0}{90},
xlabel=real axis,
ylabel=imaginary axis,
]
\addplot3[contour gnuplot={number=9,labels=false,draw color=blue}] {x^2-y^2};
\addplot3[contour gnuplot={number=9,labels=false,draw color=red}] {x*y};
\end{axis}
\end{tikzpicture}
\end{document} Here, I used draw color to change the color (which is typically mapped color for contour plots).

• Hi Christian, thanks for your help. I tried to improve my question, by introducing the original definition of the conformal mapping. I don't know the value of alpha used to build the plot, but it should be something like pi/12. – mp87 Apr 22 '12 at 9:44
• Thanks for the explanation. In this case, we find the expressions u(z) = Re[ W(z) ] and v(z) = Im[ W(z) ] with W(z) := z^(1/q). Keep in mind that z = x+iy. My suggestion is to employ an external tool to compute (sample) u(z) and v(z) (pgfplots has no complex arithmetics). gnuplot can do it if I am not mistaken, so you can employ \addplot3[contour gnuplot....] gnuplot {<expression>}; instead of my plotting expression. – Christian Feuersänger Apr 22 '12 at 14:32