LaTeX Forum

\documentclass[12pt,titlepage,a4paper]{report} 

\usepackage[pdftex]{graphicx} 
\usepackage{pgfplots}

\begin{document} 

 \begin{figure}[tbh] 
\begin{tikzpicture}
\begin{axis}[legend style={at={(0.5,1)},anchor=south , legend columns = 3}, ymajorgrids,xmajorgrids]
\addplot coordinates {(0,0) (1,1)};
\addplot coordinates {(0,1) (1,2)};
\addplot coordinates {(0,2) (1,3)};
\node[black,above] at (axis cs: 0.5,1){{\Large  testtext}};
\legend{c=1.5 ,b=1.6, a=1.4}
\end{axis}
\end{tikzpicture}
\end{figure}  
\end{document}

\documentclass[12pt,titlepage,a4paper]{report}

\usepackage{graphicx}% pdftex als Option grundsätzlich weglassen!
\usepackage{pgfplots}
\pgfplotsset{compat=1.14}% Laut Anleitung immer anzugeben!

\begin{document}

\begin{figure}[tbh]
\begin{tikzpicture}
\begin{axis}[legend style={at={(0.5,1)},anchor=south , legend columns = 3}, ymajorgrids,xmajorgrids]
\addplot coordinates {(0,0) (1,1)};
\addplot coordinates {(0,1) (1,2)};
\addplot coordinates {(0,2) (1,3)};
\node[black,fill=white,above] at (axis cs: 0.5,1){{\Large testtext}};
\legend{c=1.5 ,b=1.6, a=1.4}
\end{axis}
\end{tikzpicture}
\end{figure}
\end{document}