\documentclass[a4paper, 12pt]{article}

% a nice font
\usepackage{kpfonts}

% basic text stuff
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}

\usepackage{colortbl} % to color rows or columns of matrices

\usepackage{tikz} % main tikz package
\usepackage{tikz-network} % provides graph / network utilities (Edge, Node, etc)

\usetikzlibrary{calc} % to do some computations on the coordinates

% for a nicer colorscheme
\input{colors.tex}

\begin{document}
    \begin{tikzpicture}[>=stealth']
        \coordinate (p0) at (0,0);
        \coordinate (p1) at (0.2,0.5);
        \coordinate (p2) at (-0.3,1.0);
        \coordinate (p3) at (0.5,0);
        \coordinate (p4) at (-0.8,-0.3);
        \coordinate (p5) at (0.1,-0.3);

        \coordinate (q1) at (2.2,0.5);
        \coordinate (q2) at (2.6,0.3);
        \coordinate (q3) at (2.5,0.9);
        \coordinate (q4) at (2.8,0.9);
        \coordinate (q5) at (3.1,1.0);

        \coordinate (s0) at (0.3,2.5);
        \coordinate (s1) at (0.5,2.8);
        \coordinate (s2) at (0.7,2.5);
        \coordinate (s3) at (0.9,2.6);
        \coordinate (s4) at (0.8,3.2);
        \coordinate (s5) at (1.1,3.2);
        \coordinate (s6) at (0.9,2.2);


        \fill[blue] (p0) circle (0.1);
        \foreach \i in {1,...,5} {
            \fill[blue!50] (p\i) circle (0.1);
            \draw[->, blue, densely dashed, thin, shorten <=2.5pt, shorten >=2.5pt] (p0) -- (p\i);
        }

        \node[above=0.5cm] (c1) at (p4) {\textcolor{blue}{$\mathcal{C}_1$}};

        \foreach \i in {1,...,5} {
            \fill[green!50] (q\i) circle (0.1);
            %\draw[->, thin, shorten <=2.5pt, shorten >=2.5pt] (p0) -- (q\i);
        }

        \node[right=0.5cm] (c2) at (q2) {\textcolor{green}{$\mathcal{C}_2$}};

        \fill[red] (s6) circle (0.1);
        \foreach \i in {1,...,5} {
            \fill[red!50] (s\i) circle (0.1);
            %\draw[->, thin, shorten <=2.5pt, shorten >=2.5pt] (p0) -- (q\i);
        }

        \node[right=0.5cm] (c3) at (s4) {\textcolor{red}{$\mathcal{C}_3$}};

        \node[right, scale=0.7,below right=0.1cm and 0.4cm of p0, fill=blue!10] (a) {$\frac{1}{\left|\textcolor{blue}{\mathcal C_1}\right| - 1} \sum \left\|\begin{tikzpicture}[baseline={([yshift=-.5ex]current bounding box.center)}]
                \draw[->, >=stealth, densely dashed, thick, blue] (0.0,0.0) -- (0.3,0.4);
            \end{tikzpicture}\right\|$};

        \node[right=0.1cm of s6, scale=0.7, fill=red!10] (min) {$\min \left(
            \frac{1}{\left|\textcolor{blue}{\mathcal C_1}\right|}\sum
            \left\|\begin{tikzpicture}[baseline={([yshift=-.5ex]current bounding box.center)}]
                \draw[->, >=stealth, densely dashed, thick, red] (0.1,0.3) -- (-0.3,-0.1);
            \end{tikzpicture}\right\|,
            \frac{1}{\left|\textcolor{green}{\mathcal C_2}\right|} \sum \left\|
            \begin{tikzpicture}[baseline={([yshift=-.5ex]current bounding box.center)}]
                \draw[->, >=stealth, densely dotted, thick, red] (0,0.3) -- (0.3,-0.1);
            \end{tikzpicture} \right\| \right)$};
        %\node[below] (mean1) at (min.south east) {$\frac{1}{\left|\mathcal C_2\right|}\sum$};

        \foreach \i in {1,...,5} {
            \draw[->, shorten >=2.5pt, red, densely dotted] (s6.south east) to ($(s6.south east)!1.8cm!(q\i)$);
            \draw[->, shorten >=2.5pt, red, densely dashed] (s6.south west) to ($(s6.south west)!1.5cm!(p\i)$);
        }
    \end{tikzpicture}
\end{document}