\begin{center}

 \begin{tikzpicture}[scale=1]
\begin{axis}[
      xlabel near ticks,
      width=10cm, height=6cm,
      xlabel={Performance},
      xmin=0,xmax=10,
      ymin=0,ymax=3.5,
      xmajorticks=false,
      ymajorticks=false,
      legend style={xshift=-1em,yshift=-0.8em,legend cell align=left},
  ]

	
  \addplot[color=blue,only marks,mark size=1.0pt,] table {figures/nlpbook/data/f1.dat};
  \addplot[color=blue,fill=blue!50,opacity=0.5] table {figures/nlpbook/data/ff1.dat};
  \addplot[color=blue,only marks,mark size=2.0pt] coordinates {(3.5,1)};
  \addplot[color=blue!50] coordinates {(3.5,0.4)(3.5,1)};

  \addplot[color=red,only marks,mark size=1.0pt,] table {figures/nlpbook/data/f2.dat};
  \addplot[color=red,fill=red!50,opacity=0.5] table {figures/nlpbook/data/ff2.dat};
  \addplot[color=red,only marks,mark size=2.0pt] coordinates {(2.5,2)};
  \addplot[color=red!50] coordinates {(2.5,0.4)(2.5,2)};

  \addplot[color=ugreen,only marks,mark size=1.0pt,] table {figures/nlpbook/data/f3.dat};
  \addplot[color=ugreen,fill=ugreen!50,opacity=0.5] table {figures/nlpbook/data/ff3.dat};
  \addplot[color=ugreen,only marks,mark size=2.0pt] coordinates {(7,3)};
  \addplot[color=ugreen!50] coordinates {(7,0.4)(7,3)};
  \end{axis}

  \node[inner sep=0pt] (a) at (-1,1.25){system {\color{blue} A}};
  \node[anchor=south,inner sep=0pt] (b) at ([yshift=2.3em]a.north){system {\color{red} B}};
  \node[anchor=south,inner sep=0pt] (b) at ([yshift=2.3em]b.north){system {\color{ugreen} C}};
  \end{tikzpicture}
\end{center}

