Hello,<br><br>first the minimal example:<br>%=================%<br>\documentclass{article}<br>\pagestyle{empty}<br>\parindent0pt<br>\usepackage{pstricks}<br>\usepackage{pst-plot}<br>\usepackage{pstricks-add}<br><br>\begin{document}<br>
\def\pshlabel#1{$\tau_{#1}$}<br>  \psset{unit=1cm,%<br>      yAxisLabel={$u(t) , \widetilde{u}(t)$},xAxisLabel={$t$}}<br>     \begin{psgraph}[labels=x,ticks=x,dx=10]{-&gt;}(0,0)(-1,0)(95,3.5){10cm}{8cm}<br>            \psset{plotpoints=500,algebraic}<br>
            \psplot[linecolor=blue!70!black]{0}{90}{sqrt(sqrt(x+2))}<br>            \psclip{%<br>            \psStep[linewidth=0.8pt,linecolor=green!70!black,StepType=lower](0,90){9}{sqrt(sqrt(x+2))}<br>            \psStep[linewidth=1.5pt,linecolor=red!70!black,StepType=Riemann](0,90){9}{sqrt(sqrt(x+2))}}<br>
            \endpsclip<br>     \end{psgraph}<br>\end{document}<br>%=================%<br><br>I have the following problem the red line do not cover the green line. I hope you see it.<br><br>regards<br>Marco<br>