documentclass{scrreprt}
usepackage{amsmath,bm}
usepackage{tikz}
usetikzlibrary{arrows,matrix,positioning}

begin{document}
begin{equation}
bm{Bu}=
    begin{tikzpicture}[baseline={([yshift=-.5ex]current bounding box.center)},vertex/.style={anchor=base,
    circle,fill=black!25,minimum size=18pt,inner sep=2pt}]
    matrix [matrix of math nodes,left delimiter={[},right delimiter={]}] (m)
    {
        0 & 0 & 0 & 0  \
        0 & 0 & 0 & 0  \
        0 & 0 & 0 & 0  \
        0 & 0 & 0 & 0  \
        times & times & times & times  \
        times & times & times & times  \
        times & times & times & times  \
        times & times & times & times  \
    };
    draw[color=red] (m-1-3.north west) -- (m-1-3.north east) -- (m-8-3.south east) --              (m-8-3.south west) -- (m-1-3.north west);
    end{tikzpicture}
    begin{tikzpicture}[baseline={([yshift=-.5ex]current bounding box.center)},vertex/.style={anchor=base,
    circle,fill=black!25,minimum size=18pt,inner sep=2pt}]
    matrix [matrix of math nodes,left delimiter=(,right delimiter=)] (m)
    {
    0 \
    0 \
    times \
    0 \
    };
    draw[color=red] (m-3-1.north west) -- (m-3-1.north east) -- (m-3-1.south east) --              (m-3-1.south west) -- (m-3-1.north west);
    end{tikzpicture}
    begin{tikzpicture}
    draw [thick, black,decorate,decoration={brace,amplitude=10pt,mirror},xshift=0.4pt,yshift=-0.4pt](0,10) -- (10,10) node[black,midway,yshift=-0.6cm] {footnotesize $Form aus der\Literatur$};
    end{tikzpicture}
    =
    underbrace{
    begin{pmatrix}
    0 \ 0 \ 0 \ 0 \ times \ times \ times \ times
    end{pmatrix}
    times}_{substack{text{Ausgabe aus} \ text{Simpack}}}
label{eq:problem-state}
end{equation}
end{document}