Re: Plot3D Problem with Nonreal Numbers

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

Jim, Here is a plotting command that will produce your plot. ParametricPlot3D[ {{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 earthlink.net http://home.earthlink.net/~djmp/ >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. >--Jim > >