\psset{xunit=1cm, yunit=1cm}
%\psframebox{
\begin{pspicture}(-0.5,-0.5)(12.5,2.5)
%\psgrid(0,0)(12,2)
%\begin{pspicture}(0,0)(12, 2)
\rput[c](6,1.5){$\vec{e_1}=\left(1,0,\ldots,0\right)$\hspace{5mm}\ldots\hspace{5mm}$\vec{e_i}=\left(0,\ldots,1,\ldots,0\right)$\hspace{5mm}\ldots\hspace{5mm}$\vec{e_n}=\left(0,\ldots,0,1\right)$}
%\rput[c](6,1.5){\psframebox{$\cdot$}}
%\rput[c](4.3,1.5){\psframebox{$\vec{e_1}=\left(1,0,\ldots,0\right)$\hspace{5mm}\ldots\hspace{5mm}$\vec{e_i}=\left(0,\ldots,1,\ldots,0\right)$\hspace{5mm}\ldots\hspace{5mm}$\vec{e_n}=\left(0,\ldots,0,1\right)$}}
%\psline[arrows=->](7.9,0.5)(7.9,1.2)

\psline[arrowlength=3, arrowinset=0.1, linecolor=red]{->}(6.37,0.5)(6.37,1.3)
\rput[c](6.37,0.2){\color{red}{i. Koordinate}}

%\rput[c](0.5,0.5){.}
%\rput[c](12,2){.}

\end{pspicture}%}
%rput center --> Koordianten werden um die x-Koordinate ausgerichtet