# [pstricks] Defining a maxmum and minimum point

Arne Hallam ahallam at iastate.edu
Sun Apr 8 17:59:52 CEST 2007

So I am going to answer part of my own question.

I read a bit more carefully in the PST-3dplot manual and found a couple
of pages I had missed.  So I am part of the way there.

In the code below I seem to be making a mistake in the definition of the
function so that it points down instead of up.  I cannot see anything
obvious in my function definition.

z= 2(5x +4y -2x^2 +xy -y^2) -6x - 2y

I also want the axes to be black, and not red.

Anything obvious?

\documentclass{amsart}
\usepackage{pstricks,pst-3dplot}
\pagestyle{empty}

\begin{document}
\begin{pspicture}(-8,-10)(7,10)
%\psgrid
\psset{linecolor=black,linewidth=2pt,plotpoints=50,showpoints=false}
\pstThreeDCircle(+1,+2,0)(.4,.4,0)(.4,-.4,0)
\pstThreeDDot[drawCoor=true,linecolor=blue](+1,+2,9)
\psplotThreeD[plotstyle=ccurve,linecolor=red, drawStyle=xLines,
yPlotpoints=20, xPlotpoints=20,linewidth=0.75pt](0,4)(0,4){%
x 5 mul y 4 mul add x dup mul 2 sub x y mul add y dup sub 2 mul
x 6 mul sub y 2 mul sub}
\psset{linecolor=black,linewidth=2pt,plotpoints=50,showpoints=false}
\pstThreeDCoor[xMin=-1,yMin=-1,zMin=-6,xMax=4,yMax=4,zMax=11,linewidth=1pt]
\end{pspicture}

\end{document}

Arne Hallam wrote:
> So I was looking for an example of the something like the following for
> me to use in class.
>
> I have something I drew in Mathamatica but I ended up using a square for
> a  circular neighborhood because I don't know how to draw implicit
> circles in 3D Mathematica.  So I am now trying PSTricks which works for
> lots of other cool things.
>
>
> Show a surface in 3 dimensions (which I can easily do).
>
> Show a small circle or disc at (x1,x2,0) in the x1-x2 plane(which I
> cannot do)
>
> Show the points on the surface that lie above this disc (which I am not
> sure how to do, I know how to patch it on top of the first surface in
> different color, but that is about all)
>
> Put a point on the surface above the disc that is maximal in set (which
> I can do).
>
> I would like to add some nice lines and things, but I can do that.
>
>
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>

--
with all thy getting get understanding -- Proverbs 4:7.

In the wildness of speculation it has been suggested (of course more in jest than in earnest),that Europe ought to grow its corn in America, and devote itself solely to manufactures and commerce, as the best sort of division of the labour of the globe -- Thomas Malthus, An Essay on the Principle of Population Book III, Chapter XII.

Arne Hallam
Department of Economics