# Contour integral plot

As of now I have the code below (thanks to @AndréC), but I was hoping to also include an additional semi-circle, seen in the hand-drawn image. I am sorry, I am not so good with tikz, yet. Thank you! Here is the code:

\documentclass[border=5mm]{standalone}
\usepackage{tikz}
\usetikzlibrary{calc,decorations.markings,positioning}
\begin{document}
\begin{tikzpicture}
%configurable parameters
\def\gap{0.4}
%axes
right] at (45:\littleradius/1.5) {\large\bf{$\varepsilon$}};
\draw[line width=1pt,decoration={markings,
mark=at position 0.07 with{\arrow[line width =2pt]{>}},%{latex}},
mark=at position 0.17 with{\arrow[line width =2pt]{>}},
mark=at position 0.27 with{\arrow[line width =2pt]{>}},
mark=at position 0.35 with {\arrow[line width =2pt]{>}},%{latex}},
mark=at position 0.47 with{\arrow[line width =2pt]{>}},
mark=at position 0.53 with{\arrow[line width =2pt]{>}},%{latex}},
mark=at position 0.6 with {\arrow[line width =2pt]{>}},%{latex}},
mark=at position 0.65 with {\arrow[line width =2pt]{>}},%{latex}},
mark=at position 0.7 with{\arrow[line width =2pt]{>}},
mark=at position 0.8 with{\arrow[line width =2pt]{>}},
mark=at position 0.85 with{\arrow[line width =2pt]{>}},
mark=at position 0.955 with{\arrow[line width =2pt]{>}}},%{latex}}},
postaction={decorate}]
let
\coordinate (T) at (135:2);
\node[above] at (T){$T$};
\node[below] at (H){\Large\bf {x}};
\node[left] at (J){$\Large\bf y$};
\node[below right] at (C) {\Large\bf {C}};
\coordinate (D) at ({180-asin(\gap/2/\littleradius)}:1);            \node[above left] at (D) {$\Large\bf B$};
\coordinate (E) at ({-180+asin(\gap/2/\littleradius)}:1);           \node[below left] at (E) {$\Large\bf D$};
\node[above left] at (F) {$\Large\bf A$};
\node[below left] at (G) {$\Large\bf E$};
\coordinate (P) at (0,-4);

\node[below right] at (P) {$\Large\bf F$};
\coordinate(Q) at (3,-4);
\node[right] at (Q) {$\Large\bf G(\gamma-iT)$};
\coordinate (R) at (3,4);
\node[right] at (R) {$\Large\bf H(\gamma+iT)$};
\coordinate (S) at (0,4);
\node[above right] at (S) {$\Large\bf K$};
\end{tikzpicture}
\end{document}


and was hoping for the additional semi circle is seen to the left of the smaller-circle in the center:

EDIT: I managed to add the following, which fits for my slightly edited graph:

        \draw[thick, line width=   0.63pt] (-.9,.25) +(180:.3) arc (0:180:.3);
\draw[thick, line width=   0.63pt] (-.9,-.25) +(-180:.3) arc (0:-180:.3);


How do I get rid of the lines below the small circles, though? I want a semi-circle that does not have any bottom to it, like the one in the hand-drawn picture. Is there any way to do that with this code?

\documentclass[border=5mm]{standalone}
\usepackage{tikz}
\usetikzlibrary{calc,decorations.markings,positioning}
\begin{document}
\begin{tikzpicture}
%configurable parameters
\def\gap{0.4}
%axes
right] at (45:\littleradius/1.5) {\large\bf{$\varepsilon$}};
\draw[line width=1pt,decoration={markings,
mark=at position 0.065 with{\arrow[line width =2pt]{>}},%{latex}},
mark=at position 0.17 with{\arrow[line width =2pt]{>}},
mark=at position 0.29 with{\arrow[line width =2pt]{>}},
mark=at position 0.35 with {\arrow[line width =2pt]{>}},%{latex}},
mark=at position 0.47 with{\arrow[line width =2pt]{>}},
mark=at position 0.53 with{\arrow[line width =2pt]{>}},%{latex}},
mark=at position 0.6 with {\arrow[line width =2pt]{>}},%{latex}},
mark=at position 0.65 with {\arrow[line width =2pt]{>}},%{latex}},
mark=at position 0.7 with{\arrow[line width =2pt]{>}},
mark=at position 0.8 with{\arrow[line width =2pt]{>}},
mark=at position 0.85 with{\arrow[line width =2pt]{>}},
mark=at position 0.955 with{\arrow[line width =2pt]{>}}},%{latex}}},
postaction={decorate}]
let
in (180-\n1:\bigradius) --($(180-\n1:\bigradius)!.5! (-180-\n2:\littleradius)$)arc(180:0:\tinyradius)-- (-180-\n2:\littleradius)
arc(180-\n2:-180+\n2:\littleradius)--($(-180+\n2:\littleradius)!.5!(-180+\n1:\bigradius)!2*\tinyradius cm!(-180+\n2:\littleradius)$)arc(0:-180:\tinyradius)--(-180+\n1:\bigradius)
\coordinate (T) at (135:2);
\node[above] at (T){$T$};
\node[below] at (H){\Large\bf {x}};
\node[left] at (J){$\Large\bf y$};
\node[below right] at (C) {\Large\bf {C}};
\coordinate (D) at ({180-asin(\gap/2/\littleradius)}:1);            \node[above left] at (D) {$\Large\bf B$};
\coordinate (E) at ({-180+asin(\gap/2/\littleradius)}:1);           \node[below left] at (E) {$\Large\bf D$};
\node[above left] at (F) {$\Large\bf A$};
\node[below left] at (G) {$\Large\bf E$};
\coordinate (P) at (0,-4);

\node[below right] at (P) {$\Large\bf F$};
\coordinate(Q) at (3,-4);
\node[right] at (Q) {$\Large\bf G(\gamma-iT)$};
\coordinate (R) at (3,4);
\node[right] at (R) {$\Large\bf H(\gamma+iT)$};
\coordinate (S) at (0,4);
\node[above right] at (S) {$\Large\bf K$};
\end{tikzpicture}
\end{document}

• André I cannot thank you enough. To get a general idea how you did this, would you recommend the tikz-manual?
– user212817
Aug 30, 2020 at 19:24
• The code covers several concepts explained in the manual. Referring to the manual is therefore very long. It's simpler if you say what you don't quite understand, I'll do my best to explain it to you. Aug 30, 2020 at 19:35
• Surprisingly I actually do understand some of the new code, but I do not know how to get there myself. Rather, I am asking whether or not the manual would be the best place to learn this so I could do it myself. I really appreciate the help -- just looking for more structured learning.
– user212817
Aug 30, 2020 at 19:54
• I learned from the TikZ manual. The new code is explained in the calc library. The principle of this library is simple: changes can be made one after the other, which I did. The simplicity of the principle induces on the other hand a complexification of the code. Aug 30, 2020 at 20:00
• Alright I will read that portion, thank you again for your time!
– user212817
Aug 30, 2020 at 20:01