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Re: Plot3D Problem with Nonreal Numbers

  • To: mathgroup at
  • Subject: [mg20050] Re: [mg20032] Plot3D Problem with Nonreal Numbers
  • From: "David Park" <djmp at>
  • Date: Sat, 25 Sep 1999 18:46:12 -0400
  • Sender: owner-wri-mathgroup at


Here is a plotting command that will produce your plot.

   {{r*Cos[t], Sqrt[-4 + r^2], r*Sin[t]}, 
    {r*Cos[t], -Sqrt[-4 + r^2], 
     r*Sin[t]}}, {r, 2, 10}, 
   {t, 0, 2*Pi}, PlotPoints -> {15, 31}, 
   Axes -> False, Boxed -> False, 
   ViewPoint -> {1.45, -2.676, 1.479}]; 

I am sending you a notebook separately which gives more details.

David Park
djmp at

>Greetings All!
>I'm hoping you can help this struggling artist generate this 3D plot
>destined for a calculus textbook. If the author had provided me with a
>notebook file I wouldn't have to be bothering you, but he didn't. All I
>have is a sketch of something that resembles two funnels joined at the
>narrow end and this equation:
>x^2 - y^2 + z^2 = 4
>I have solved for z and used the results in Plot3D but this generates an
>error for the points that are not real numbers and only a portion of the
>plot is drawn.
>The question is, is there a way to make Mathematica ignore the solutions
>that are not real? Or is there some other technique I should be using to
>render this graphic.
>Be gentle. Remember I'm an artist, not a mathematician.
>Thanks in advance for any and all assistance.

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