% Dans le préambule
% -----------------
\usepackage{pstricks-add}
% -----------------

\psset{xunit=4cm,yunit=2cm,algebraic}
\begin{pspicture}(-0.3,-1)(1.3,1.3)

\newcommand{\s}{cos(2*\psPi*x)/(x^2+1)}

\psStep[StepType=infimum,fillstyle=solid,
        fillcolor=green](0,1){25}{\s}

\psplot{0}{1.2}{\s}

\psaxes{->}(0,0)(0,-1)(1.3,1.3)
\end{pspicture}