draw a circle - latex code

Question

I want to create the following picture, how should i proceed?

Thanks!

Look around here, as a start: http://tex.stackexchange.com/questions/88308/how-to-generate-n-points-on-a-circumference-and-connect-all-of-them-while-having?rq=1 — Matsmath, Aug 22 '16 at 20:05

score 5 · Accepted Answer · answered Aug 22 '16 at 20:21

The following example uses an uniform distribution of the points/angles.

\documentclass{article}
\usepackage{tikz}

\begin{document}
\begin{tikzpicture}
  \def\Radius{20mm}
  \draw
    (0, 0) coordinate (M) circle[radius=\Radius]
  ;
  % Full circle evenly divided into 14 pieces
  \filldraw[fill=white, radius=2pt]
    \foreach \i in {0, ..., 3, 12, 13} {
      (M) +(90 - \i * 360/14:\Radius) circle[]
    }
  ;
  \path
    \foreach \i/\a in {0/1, 1/2, 2/3, 3/4, 12/20, 13/21} {
      (M) -- node[pos=.8] {$a_{\a}$} +(90 - \i * 360/14:\Radius)
    }
  ;
  \fill[radius=1.5pt]
    \foreach \i in {4, ..., 11} {
      (M) +(90 - \i * 360/14:.8*\Radius) circle[]
    }
  ;
\end{tikzpicture}
\end{document}

thanks for your answer. please, tell me from where do you learn programming in latex? can you recommend some books? — Iuli, Aug 23 '16 at 14:27
@Iuli Learning by doing, TikZ manual, answering questions, ... — Heiko Oberdiek, Aug 23 '16 at 16:24

draw a circle - latex code

1 Answers1