       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

```

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