%
% carlsonpath.tex -- template for standalon tikz images
%
% (c) 2021 Prof Dr Andreas Müller, OST Ostschweizer Fachhochschule
%
\documentclass[tikz]{standalone}
\usepackage{amsmath}
\usepackage{times}
\usepackage{txfonts}
\usepackage{pgfplots}
\usepackage{csvsimple}
\usetikzlibrary{arrows,intersections,math}
\begin{document}
\def\skala{1}
\begin{tikzpicture}[>=latex,thick,scale=\skala]

\definecolor{darkgreen}{rgb}{0,0.6,0}

\def\xh{0.001}
\def\r{4.6}
\pgfmathparse{asin(\xh/\r)}
\xdef\w{\pgfmathresult}

\draw[->] (-1.1,0) -- (7.4,0) coordinate[label=$\operatorname{Re}z$];
\draw[->] (0,-5.2) -- (0,5.4) coordinate[label={right:$\operatorname{Im}z$}];

\draw[->,color=red,line width=0.5pt] (0,0) -- (50:\r);
\node at (50:{0.7*\r}) [left] {$R$};

\node[color=red] at (-30:\r) [below right] {$C_1$};

\draw (-0.1,\r) -- (0.1,\r);
\draw (-0.1,-\r) -- (0.1,-\r);
\node at (-0.1,-\r) [left] {$-R$};
\node at (-0.1,\r) [left] {$R$};

\draw[color=red,line width=1.4pt]
	({-90+\w}:\r) arc ({-90+\w}:{90-\w}:\r)
	--
	cycle;
\draw[->,color=red,line width=1.4pt] (-30:\r) -- (-31:\r);
\draw[->,color=red,line width=1.4pt] (30:\r) -- (29:\r);
\draw[->,color=red,line width=1.4pt] (\xh,{0.5*\r}) -- (\xh,{0.5*\r+0.1});
\draw[->,color=red,line width=1.4pt] (\xh,{-0.5*\r}) -- (\xh,{-0.5*\r+0.1});

\def\a{2.6}
\def\xstep{0.7}

\foreach \k in {1,...,10}{
	\fill[color=blue] ({\k*\xstep},0) circle[radius=0.08];
	\node at ({\k*\xstep},0) [below] {$\k$};
}

\fill[color=darkgreen] (\a,0) circle[radius=0.08];
\node[color=darkgreen] at (\a,0) [above] {$a$};

\end{tikzpicture}
\end{document}