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RE: A 3D Plot Query

  • To: mathgroup at smc.vnet.net
  • Subject: [mg94261] RE: [mg94222] A 3D Plot Query
  • From: "David Park" <djmpark at comcast.net>
  • Date: Tue, 9 Dec 2008 06:59:04 -0500 (EST)
  • References: <31362096.1228736527369.JavaMail.root@m02>

Sid,

Not silly at all.

Use cylindrical coordinates and ParametricPlot3D to get a surface with a
circular base.

Use the ViewPoint option to get the x and y axes in the position you want.

With[{a = 5},
 ParametricPlot3D[{r Cos[\[Theta]], r Sin[\[Theta]], 
   2 - r^2}, {\[Theta], 0, 2 \[Pi]}, {r, 0, a},
  PlotPoints -> {30, 10},
  MaxRecursion -> 3,
  AxesLabel -> {"x", "y", "z"},
  ViewPoint -> {5, 5, 3},
  BoxRatios -> {1, 1, 1}]
 ]


David Park
djmpark at comcast.net
http://home.comcast.net/~djmpark/  


From: pcoords29 at gmail.com [mailto:pcoords29 at gmail.com] 


Hi,

This may sound silly, but I can't get it to work. (I'm using v 6.0)

How do I get my 3D plots look as given in textbooks, ie. with the y-
axis pointing to the right, the z-axis up and x-axis pointing out of
the paper/screen ( showing the first octant)?  I mean the kind of
plots one draws on paper when working out surface integrals  in
Calculus classes.

If this is of any help, I'd like to get the plot of  the paraboloid

 z = 2-(x^2+y^2),  as given in Fig. 10-10  of  Spiegel's Advanced
Calculus, Schaum Series.

I tried

        Plot3D[2 - (x^2 + y^2), {x, -a, a}, {y, -a, a}],

with various values of a. Unfortunately, none of them look like the
traditional cap-shaped paraboloid.

Thanks for any help.

Sid.







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