Add some arrows on the picture

Question

I want to use tikz to draw the following picture:

. Is there any good way to add the arrow like that and how can we draw a circle from start point to end point.

Answer 1

The information on how to place arrow tips midway can be found in several postings on this site. However, these usually miss the fine positioning of the arrow needed here because of the curvature, hence once more. The relevant part of the code below is

mark=at position 0.5 with {\arrow[xshift=2pt]{Latex[length=4pt]}}

with the following elements. 0.5 specifies the position of the arrow tip and may vary between 0 (start of path) and 1 (end of path). Latex specifies the type of arrow; see the tikz manual for the options offered by the library arrows.meta. [length=4pt] specifies details of the arrow type like its length; other options used below are open (to obtain an outlined arrow) and fill=white (to make the interior of the arrow cover the line below it). [xshift=2pt] specifies details regarding the positioning of the arrow tip; without this option the arrow is positioned with its tip, which looks misplaced on bent lines.

\documentclass[border=2mm]{standalone}
\usepackage{tikz}
\usetikzlibrary{decorations.markings,arrows.meta}
\tikzset
  {midarrow/.style={decoration={markings,mark=at position 0.5 with
     {\arrow[xshift=2pt]{Latex[length=4pt,#1]}}},postaction={decorate}}
  }
\begin{document}
\begin{tikzpicture}
  \draw[midarrow] (0,0) -- (1,0);
  \draw[midarrow={open,fill=white}] (0,0) arc(-90:180:10pt);
\end{tikzpicture}
\end{document}

---

Recycling some ideas from another post, you can draw the graphs by defining a "language" of arcs and lines.

% arcs and lines
\documentclass{article}
\usepackage[margin=1.5cm]{geometry}
\pagestyle{empty}

\usepackage{tikz}
\usetikzlibrary{decorations.markings,arrows.meta}

\newcommand\ALloop[1]%
  {\ifx\relax#1%
   \else
     \ifcsname AL:#1\endcsname
       \csname AL:#1\endcsname
     \else
       \GenericError{(AL)}{AL Error: operator #1 undefined}{}{}%
     \fi
   \expandafter\ALloop
   \fi
  }

\newcommand\AL[1]%
  {\begin{tikzpicture}[thick,every node/.style={blob}]
   \coordinate(X) at (0,0);
   \ALloop#1\relax
   \end{tikzpicture}
  }

\def\ALs{12}% small radius
\pgfmathsetmacro\ALm{1.5*\ALs}% medium radius
\pgfmathsetmacro\ALl{2.25*\ALs}% large radius
\pgfmathsetmacro\ALh{3*\ALs}% huge radius
\pgfmathsetmacro\ALt{sqrt(3)*\ALh}% side of triangle
\pgfmathsetmacro\ALa{0.75*\ALs}% length of arrow
\pgfmathsetmacro\ALn{0.4*\ALs}% size of node

\tikzset
  {midarrow/.style={decoration={markings,mark=at position 0.5 with
     {\arrow[xshift=0.5*\ALa]{Latex[length=\ALa pt,#1]}}},postaction={decorate}},
   full/.style={midarrow},
   open/.style={midarrow={open,fill=white}},
   blob/.style={circle,draw,fill,minimum size=\ALn pt,inner sep=0pt,outer sep=0pt}
  }

\newcommand\arrowtype{full}
% \ARC{start angle}{delta angle clockwise}{radius}
\newcommand\ARC [3]{\draw[\arrowtype] (X) arc(#1:#1-#2:#3) node{} coordinate (X);}
% \LINE{angle}{length}
\newcommand\LINE[2]{\draw[\arrowtype] (X) -- +(#1:#2) coordinate (X);}

\newcommand\ALdef[1]{\expandafter\def\csname AL:#1\endcsname}
\ALdef{a}{\ARC{ 30}{360}{\ALs pt}}
\ALdef{b}{\ARC{150}{360}{\ALs pt}}
\ALdef{c}{\ARC{270}{360}{\ALs pt}}
\ALdef{d}{\ARC{  0}{360}{\ALm pt}}
\ALdef{e}{\ARC{180}{360}{\ALm pt}}
\ALdef{f}{\ARC{  0}{180}{\ALl pt}}
\ALdef{g}{\ARC{180}{180}{\ALl pt}}
\ALdef{h}{\ARC{ 30}{120}{\ALh pt}}
\ALdef{i}{\ARC{150}{120}{\ALh pt}}
\ALdef{j}{\ARC{270}{120}{\ALh pt}}
\ALdef{k}{\ARC{210}{-120}{\ALh pt}}
\ALdef{0}{\LINE{  0}{\ALt pt}}
\ALdef{1}{\LINE{ 60}{\ALt pt}}
\ALdef{2}{\LINE{120}{\ALt pt}}
\ALdef{3}{\LINE{180}{\ALt pt}}
\ALdef{4}{\LINE{240}{\ALt pt}}
\ALdef{5}{\LINE{300}{\ALt pt}}
\ALdef{F}{\def\arrowtype{full}}
\ALdef{O}{\def\arrowtype{open}}

\begin{document}
\renewcommand\arraystretch{5}
\section*{The operators}

\begin{tabular}[t]{ll}
\verb"\AL{a}" & \AL{a}\\
\verb"\AL{b}" & \AL{b}\\
\verb"\AL{c}" & \AL{c}\\
\verb"\AL{d}" & \AL{d}\\
\verb"\AL{e}" & \AL{e}\\
\verb"\AL{f}" & \AL{f}\\
\verb"\AL{g}" & \AL{g}\\
\verb"\AL{h}" & \AL{h}\\
\verb"\AL{i}" & \AL{i}\\
\verb"\AL{j}" & \AL{j}\\
\verb"\AL{k}" & \AL{k}
\end{tabular}
\quad
\begin{tabular}[t]{ll}
\verb"\AL{0}" & \AL{0}\\
\verb"\AL{1}" & \AL{1}\\
\verb"\AL{2}" & \AL{2}\\
\verb"\AL{3}" & \AL{3}\\
\verb"\AL{4}" & \AL{4}\\
\verb"\AL{5}" & \AL{5}\\
\verb"\AL{F}" & switch to full arrows\\
\verb"\AL{O}" & switch to open arrows
\end{tabular}

\newpage
\section*{Examples}

\begin{tabular}{ll}
\verb"\AL{OdFgOgFeOfFf}" &
\AL{OdFgOgFeOfFf} \\
\verb"\AL{OjihF204}" &
\AL{OjihF204} \\
\verb"\AL{OjihF135}" &
\AL{OjihF135} \\
\verb"\AL{FjObFiOaFhOc}" &
\AL{FjObFiOaFhOc} \\
\verb"\AL{OjFbOiFaOhFc}" &
\AL{OjFbOiFaOhFc} \\
\verb"\AL{OjiF3kOhFc}" &
\AL{OjiF3kOhFc} \\
\verb"\AL{FjiO3kFhOc}" &
\AL{FjiO3kFhOc}
\end{tabular}
\end{document}