\documentclass{article}
\usepackage[usenames]{color}
\usepackage{gastex}

\begin{document}

% curves

\begin{center}
\begin{picture}(120,40)(0,0)
%   \put(0,0){\framebox(120,40){}}
  \put(2,3){
    \unitlength=8mm
    \drawline[AHnb=0](0,0)(0,2)(1,3)(0,4)(2,4)(2,2)(4,0)(2,0)(1,1)
    \drawcurve[linecolor=Red,AHnb=0](0,0)(0,2)(1,3)(0,4)(2,4)(2,2)(4,0)(2,0)(1,1)
  }
  \put(55,16){
    \unitlength=1.5mm
    \drawline[AHnb=0](-10,-10)(10,10)(-10,10)(10,-10)
    \drawcurve[linecolor=Red,ATnb=3,AHnb=4](-10,-10)(10,10)(-10,10)(10,-10)
  }
  \put(100,19){
    \unitlength=20mm
    \drawline[AHnb=0](0.95,0.3)(-0.59,-0.8)(0,1)(0.59,-0.8)(-0.95,0.3)
    \drawcurve[linecolor=Red](0.95,0.3)(-0.59,-0.8)(0,1)(0.59,-0.8)(-0.95,0.3)
  }
\end{picture}
\end{center}

\end{document}