begin{document}
begin{tikzpicture}
  begin{axis}
          [
        ,width=7cm[![enter image description here][1]][1]
       ,xtick={0,0.04,0.05,0.06,0.07,0.08,0.09,0.1,0.11,0.12,0.14433756729,0.16867512,0.17867512,0.18867512,0.19867512,0.20867512,0.21867512,0.22867512,0.23867512,0.24867512,0.25867512}
        ,xticklabels={,,scalebox{.4}{$d_m$}, ,, ,, ,,,,,,,,,,scalebox{.4}{$d_{r+1}$},scalebox{.4}{$d_r$}, scalebox{.4}{$d_{r-1}$},,,,,,,,,,,,,,,scalebox{.4}{$d_{1}$},scalebox{.4}{$d_{0}$}}
        ]
    addplot[blue, domain = 0:sqrt(3)/6]{testfunction(x)};
  end{axis}
end{tikzpicture}
end{document}