Re: Re: Model the surface of an ellipsoid

*To*: mathgroup at smc.vnet.net*Subject*: [mg93567] Re: [mg93549] Re: Model the surface of an ellipsoid*From*: Bob Hanlon <hanlonr at cox.net>*Date*: Fri, 14 Nov 2008 06:42:24 -0500 (EST)*Reply-to*: hanlonr at cox.net

a = 3; b = 2; eqn = x^2/a^2 + y^2/b^2 == 1; soln = y /. Solve[eqn, y] {(-(2/3))*Sqrt[9 - x^2], (2*Sqrt[9 - x^2])/3} Plot[soln, {x, -a, a}, AspectRatio -> b/a] a = 3; b = 2; c = 1; eqn = x^2/a^2 + y^2/b^2 + z^2/c^2 == 1; soln = z /. Solve[eqn, z] {(-(1/6))*Sqrt[-4*x^2 - 9*y^2 + 36], (1/6)*Sqrt[-4*x^2 - 9*y^2 + 36]} Plot3D[soln, {x, -a, a}, {y, -b, b}, BoxRatios -> {a, b, c}] Bob Hanlon ---- Mayneord <xrayspectrum at googlemail.com> wrote: ============= On Nov 13, 12:34 pm, Jens-Peer Kuska <ku... at informatik.uni-leipzig.de> wrote: > Hi, > > and > > http://mathworld.wolfram.com/Ellipsoid.html > > has no parametric or implicit equation for you ? > And you can't even download the notebookhttp://mathworld.wolfram.com/note= books/Surfaces/Ellipsoid.nb > > ?? > Too bad > > Regards > Jens Hi Jens, Thank you so much for your reply. when i wrote this post, I was sure that i will get a reply from you first ;-) I already download the notebook long ago. I did not understand anything from that it seems to be too much of mathematics to me. In my case i have only 4 unknown parameters ( 1 = Sqrt[r^2/R^2 + d^2/ D^2] ). Typically, also shown in the websitehttp://mathworld.wolfram.com/El= lipsoid.html, for a ellipsoidal there must at least three coordinates. But the equation which is i have seems to be different. please tell me if am wrong. Please understand i am using mathematica 5.2. I used an ImplicitPlot like this i get only 2D plot. ImplicitPlot[Sqrt[(x^2/9) + (y^2/4)] == 1, {x, -3, 3}] My question is for 3D it is more complicated? do i need to use much of trigonometry for the angles? thanks again May -- Bob Hanlon