[pstricks] I need a little help

[Juergen Gilg]

Dear Cyrille,

here a try for the green intersecting curve:

\documentclass{article}
\usepackage{pst-solides3d}

\begin{document}
  \begin{center}
  \psset{lightsrc=viewpoint,viewpoint=40 30 16 rtp2xyz,Decran=20}
  \begin{pspicture}(-4,-4)(4,4)
  \psSurface[fillcolor=cyan!10,%algebraic,%axesboxed,
   ngrid=.25 .25,incolor=yellow,linewidth=0.125\pslinewidth,grid,
   intersectionplan={[0 0 1 -8.4] [0 0 1 -3.6] },
   intersectioncolor=(bleu) (rouge),
   intersectionlinewidth=1  1,
   intersectiontype=0,](-3,-3)(15,15){ x 4 sub dup mul y 4 sub dup mul 
add -5 div 10 add
     dup -2 lt {pop -2}if }
%  {-((x-4)^2+(y-4)^2)*0.2+10}
  \axesIIID[linecolor=gray,linewidth=0.4pt,labelsep=18pt](0,0,0)(13,13,12)
\psLineIIID[linecolor=blue, linewidth=0.1pt,linearc=0.,
  doubleline=false](0,0,0)(6,0,0)(6,6,0)(6,6,8.4)
\psLineIIID[linecolor=blue, linewidth=0.1pt,linearc=0.,
  doubleline=false](0,0,0)(0,6,0)(6,6,0)
\psLineIIID[linecolor=red, linewidth=0.1pt,linearc=0.,
  doubleline=false](0,0,0)(8,0,0)(8,8,0)(8,8,3.6)
\psLineIIID[linecolor=red, linewidth=0.1pt,linearc=0.,
  doubleline=false](0,0,0)(0,8,0)(8,8,0)
\defFunction[algebraic]{inter}(t){t}{t}{-(t-4)^2*0.4+10}
\psSolid[object=courbe,r=0,linecolor=green,linewidth=1pt,range=3 9, 
ngrid=.15 .15,
         function=inter,grid,action=draw]
%\pscurve[linecolor=green](-0.32,0.45)(-0.33,.9)(-0.6,2.4)
\rput(-1.8,-.2){\tiny $x_1$}
\rput(-1,-.1){\tiny $x_0$}
\rput(.8,-0.2){\tiny $y_0$}
\rput(1.2,-.5){\tiny $y_1$}
\rput(-2.5,.4){\tiny $U_0$}
  \end{pspicture}
  \end{center}
\end{document}

Hope this helps!

Regards,

Jürgen