<table cellspacing="0" cellpadding="0" border="0" ><tr><td valign="top" style="font: inherit;">Hi folks,<br><br>I've been trying out the package pst-solides3d to create a visual interpretation of the directional derivative. Here is the code:<br><br><br>\documentclass{article} % geometric interpretation of directional derivative. <br>%Draft written by José Agapito Ruiz<br><br>\usepackage{pstricks}%<br>\usepackage{pst-solides3d}<br>\usepackage{pst-3dplot}%<br><br>\thispagestyle{empty}<br><br>\begin{document}<br><br>\psset{viewpoint=50 40 30 rtp2xyz,Decran=50}%<br>\psset{lightsrc=viewpoint,linewidth=0.5\pslinewidth}%<br><br>\begin{pspicture}(-6,-4)(7,12)<br>%\psgrid<br>\psSolid[object=grille,name=baseplane,base=-4 4 -4 4,action=draw,linecolor=lightgray]%<br>\psSurface[%<br> fillcolor=cyan!50,<br>% tracelignedeniveau=true,<br>% hauteurlignedeniveau=5,<br>% linewidthlignedeniveau=3,<br>%
couleurlignedeniveau=blue,<br> intersectionplan={[2 -1 0 -3]},<br> intersectioncolor=(rouge),<br> intersectionlinewidth=1.5,<br> intersectiontype=0,<br> ngrid=.15 .15,incolor=yellow,algebraic,<br> axesboxed,Zmin=0,Zmax=10](-4,-4)(4,4){%<br> (-(x-3)^2-2*(y-1)^2+90)/10 }%<br><br>%%% lines passing through the points at the domain and at the surface<br>%<br>\psSolid[object=line,args=-0.5 -4 0 4.25 5.5 0,linewidth=1.5pt,linestyle=dashed,linecolor=blue]% line in the direction of (1,2,0) on XY plane<br>\psSolid[object=line,args=-0.5 -4 8.775 4.25 5.5 8.775,linewidth=1.5pt,linestyle=dashed,linecolor=blue]% line parallel to the above one on plane z=8.775<br>\pstThreeDPut(-1.95,-0.525,7.97){\psSolid[object=line,args=-0.5 -4 0.1 3.5 4 -0.9,linewidth=1.5pt,linecolor=black]}% tangent line to the surface at
(2.5,2,8.775)<br>%%%<br><br><br>%%% vector<br>%<br>\psSolid[object=vecteur,definition=vecteur3d, args=2 1 0 2.5 2 0,linecolor=blue,<br>linewidth=2pt](2.5,2,0)% vector (1,2,0)<br>%%%<br><br><br>%%% points at the surface and at the domain<br>%<br>\psSolid[object=point,args=2.5 2 8.775,dotsize=1pt 1,linecolor=blue]% point at the surface<br>\psSolid[object=point,args=2.5 2 0,dotsize=1pt 1,linecolor=blue]% point at the domain<br>%%%<br><br><br>%%% transparent plane perpendicular to XY plane and in the direction of vector %(1,2,0)<br>%<br>\psSolid[fillcolor=white!40,opacity=0.2,object=plan,<br> definition=equation,args={[2 -1 0 -3]}, base=-5.3 7.4 -4 7.5](-3.6,-4.5,0)%<br>%%%<br><br>\end{pspicture}<br><br>\end{document}<br><br>===============================<br><br>I came out with the following questions.<br><br>1. The command \psSurface has the option of drawing the curve that results of intersecting a defined surface with a plane. Is it
possible to label such a curve for further use later on?<br><br>2. Is there a direct way to plot the tangent line to the curve that results of intersecting a defined surface with a plane? I did this manually combining the command \pstThreeDPut of the pst-3dplot package with the command \psSolid and then <br>figuring out the coordinates by trial and error. Another way I can think of is to figure out the coordinates of such a tangent line by simple inspection by using \psgrid and then to use the \psline command. But there must be certainly a most efficient way of doing this.<br><br>3. How do we translate a line object? I tried for instance <br><br>\psSolid[object=line,args=-0.5 -4 8.775 4.25 5.5 8.775,linewidth=1.5pt,linestyle=dashed,linecolor=blue](a,b,c) to place the line at the point (a,b,c) but it didn't work. However, it did work with object=plan.<br><br>4. Following the previous question, what is the center of an object=plan? I translate such
an object to a point (a,b,c) but I did it more or less by trial and error.<br><br>5. Finally, I tried to use linestyle=none as an option in the \psSolid command for the object=plan, but it did not work.<br><br>Thank you for your time.<br><br>Best regards,<br><br>José Agapito.<br></td></tr></table><br>