\documentclass{article}
\usepackage{tikz}
\usepackage{pgf}
\usepackage{pgfplots}

\pgfplotsset{compat=1.15}


%% DATA for the graphs: first x coordinate, second y coordinate
\begin{filecontents}{re-python2.data}
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\end{filecontents}

\begin{filecontents}{re-java.data}
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\end{filecontents}



\begin{document}

\section*{Benchmarks for $(a^*)^* b$ and $a^{?\{n\}} a^{\{n\}}$}

\mbox{}\bigskip

\begin{center}
$(a^*)^* \cdot b$ and strings $\underbrace{a\ldots a}_{n}$\medskip\\
\begin{tabular}{@{}cc@{}}
\raisebox{5mm}{
\begin{tikzpicture}
\begin{axis}[
    xlabel={$n$},
    x label style={at={(1.05,0.0)}},
    ylabel={time in secs},
    enlargelimits=false,
    xtick={0,5,...,30},
    xmax=33,
    ymax=35,
    ytick={0,5,...,30},
    scaled ticks=false,
    axis lines=left,
    width=5cm,
    height=5cm, 
    legend entries={Java, Python},  
    legend pos=north west,
    legend cell align=left]
\addplot[blue,mark=*, mark options={fill=white}] table {re-python2.data};
\addplot[cyan,mark=*, mark options={fill=white}] table {re-java.data};
\end{axis}
\end{tikzpicture}}
&
\begin{tikzpicture}
  \begin{axis}[
    xlabel={$n$},
    x label style={at={(1.1,0.0)}},
    ylabel={time in secs},
    enlargelimits=false,
    ymax=35,
    ytick={0,5,...,30},
    axis lines=left,
    width=6.5cm,
    height=5cm,
    legend entries={Derivative matcher},  
    legend pos=north east,
    legend cell align=left]
\addplot[black,mark=square*,mark options={fill=white}] table {re3a.data};
\end{axis}
\end{tikzpicture}
\end{tabular}
\end{center}\bigskip

\begin{center}
$a^{?\{n\}} \cdot a^{\{n\}}$ and strings $\underbrace{a\ldots a}_{n}$\medskip\\
\begin{tabular}{@{}cc@{}}
\begin{tikzpicture}
\begin{axis}[
    xlabel={$n$},
    x label style={at={(1.05,0.0)}},
    ylabel={\small time in secs},
    enlargelimits=false,
    xtick={0,5,...,30},
    xmax=33,
    ymax=35,
    ytick={0,5,...,30},
    scaled ticks=false,
    axis lines=left,
    width=5cm,
    height=5cm, 
    legend entries={Python,Ruby},  
    legend pos=north west,
    legend cell align=left]
\addplot[blue,mark=*, mark options={fill=white}] table {re-python.data};
\addplot[brown,mark=triangle*, mark options={fill=white}] table {re-ruby.data};  
\end{axis}
\end{tikzpicture}
&
\begin{tikzpicture}
  \begin{axis}[
    xlabel={$n$},
    x label style={at={(1.1,0.05)}},
    ylabel={\small time in secs},
    enlargelimits=false,
    xtick={0,2500,...,11000},
    xmax=12000,
    ymax=35,
    ytick={0,5,...,30},
    scaled ticks=false,
    axis lines=left,
    width=6.5cm,
    height=5cm,
    legend entries={Derivative matcher},  
    legend pos=north east,
    legend cell align=left]
\addplot[black,mark=square*,mark options={fill=white}] table {re3.data};
\end{axis}
\end{tikzpicture}
\end{tabular}
\end{center}



\end{document}




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