Hmmm. I don't know how Mathematica plots in 3D, but you have a problemat, for 
example, the x,y coordinates (0,10). The Z output appears to be almost 15.
In the ellipse equation, if you do 
(9^2 * (1 - (0 +(10/4)^2)))^0.5
you clearly end up with a complex number, 0j14.7.
i.e. Mathematica, for whatever reason is plotting the imaginary coordinate when 
z is outside the bounds of the ellipse, perhaps. Regardless, I think, as has 
been said previously, you need to parameterize the equation.
> Date: Sat, 7 Mar 2015 03:11:02 -0600
> From: s...@caveconsulting.com
> To: programm...@jsoftware.com
> Subject: Re: [Jprogramming] Plotting a 3D Ellipse
> 
>  No,
> Mathematica has operator precedence   ^ * /  + -
> So you don't need the parenthesis. However, I put them in anyway - same
> result
> 
> http://bit.ly/17ZqQjI
> 
> Skip Cave
> Cave Consulting LLC
> 
> On Sat, Mar 7, 2015 at 3:04 AM, Jon Hough <jgho...@outlook.com> wrote:
> 
> > Ah,
> > It seems you are not doing 1 - (x^2 +y^2).
> > i.e. your parentheses are messed up.in you (mathematica ?) code you need
> > to do
> > (c^2)*(1 - ((x/a)^2+(y/b)^2))^0.5
> > i.e. sum the x and y terms and then subtract them both from 1.
> > (Note: i don't know mathematica syntax, but I assume the above is valid.)
> >
> > > Date: Sat, 7 Mar 2015 02:59:48 -0600
> > > From: s...@caveconsulting.com
> > > To: programm...@jsoftware.com
> > > Subject: Re: [Jprogramming] Plotting a 3D Ellipse
> > >
> > > Jon,
> > >
> > > Well that made it DIFFERENT, but still not an ellipse...
> > >
> > > http://bit.ly/17ZqbyM
> > >
> > > Skip
> > >
> > > Skip Cave
> > > Cave Consulting LLC
> > >
> > > On Sat, Mar 7, 2015 at 2:38 AM, Jon Hough <jgho...@outlook.com> wrote:
> > >
> > > > I think I can see 2 issues:1. you need to multiply by c^2 , not c.2.
> > you
> > > > need to sqrt the whole thing.
> > > >
> > > >
> > > > > Date: Sat, 7 Mar 2015 02:32:38 -0600
> > > > > From: s...@caveconsulting.com
> > > > > To: programm...@jsoftware.com
> > > > > Subject: Re: [Jprogramming] Plotting a 3D Ellipse
> > > > >
> > > > > Well, I tried plotting the equation
> > > > > z = (c*(1 - ((x^2)%(a^2)) + ((y^2)%(b^2))))
> > > > >
> > > > > And I don't get anything like a ellipsoid. Here's what I get...
> > > > > http://bit.ly/17Zou4t
> > > > > What is going wrong?
> > > > >
> > > > > Skip Cave
> > > > > Cave Consulting LLC
> > > > >
> > > > > On Sat, Mar 7, 2015 at 12:04 AM, Skip Cave <s...@caveconsulting.com>
> > > > wrote:
> > > > >
> > > > > > Yes, I just solved the Cartesian equation, and got the same
> > answer. I
> > > > just
> > > > > > need the positive values of z, so I can take the absolute value of
> > the
> > > > > > equation for the plot.
> > > > > >
> > > > > > Now I need to see if I can plot the ellipse by simply running x
> > from
> > > > 1-10,
> > > > > > and then stepping y after each x pass. I want to see the zero
> > values
> > > > of x
> > > > > > as well, making a plane that the half ellipse sets on.
> > > > > >
> > > > > > Skip
> > > > > >
> > > > > > On Mar 6, 2015 11:20 PM, "Raul Miller" <rauldmil...@gmail.com>
> > wrote:
> > > > > > >
> > > > > > > Of course you realize that there are either two or zero values
> > of z
> > > > > > > for every value of x and y.
> > > > > > >
> > > > > > > That said,
> > > > > > >    (((x^2)%(a^2)) + ((y^2)%(b^2)) + ((z^2)%(c^2))) = 1
> > > > > > >   (((c^2)*((x^2)%(a^2)) + ((y^2)%(b^2)))+ ((z^2)) = c^2
> > > > > > >   (z^2) = (c^2)*(1 - ((x^2)%(a^2)) + ((y^2)%(b^2)))
> > > > > > >
> > > > > > > a=:3
> > > > > > > b=:4
> > > > > > > c=:5
> > > > > > >
> > > > > > >    z=:13 :'c * ((1 - ((x^2)%(a^2)) + ((y^2)%(b^2))))^0.5'
> > > > > > >    z
> > > > > > > 5 * 0.5 ^~ 1 - (9 %~ 2 ^~ [) + 16 %~ 2 ^~ ]
> > > > > > >
> > > > > > > Or:
> > > > > > >    z=:1 _1 */ c * 0.5 ^~ 1 - ((a^2) %~ 2 ^~ [) + (b^2) %~ 2 ^~ ]
> > > > > > >
> > > > > > > Does that help?
> > > > > > >
> > > > > > > Thanks,
> > > > > > >
> > > > > > > --
> > > > > > > Raul
> > > > > > >
> > > > > > > On Sat, Mar 7, 2015 at 12:10 AM, Skip Cave <
> > s...@caveconsulting.com>
> > > > > > wrote:
> > > > > > > > Raul,
> > > > > > > >
> > > > > > > > Yes. What I need is a function f (x,y) using the Cartesian
> > > > coordinates
> > > > > > x &
> > > > > > > > y that will produce the z dimension in the ellipse when I step
> > x &
> > > > y
> > > > > > over
> > > > > > > > the plane.
> > > > > > > >
> > > > > > > > Skip
> > > > > > > >
> > > > > > > > Skip Cave
> > > > > > > > Cave Consulting LLC
> > > > > > > >
> > > > > > > > On Fri, Mar 6, 2015 at 11:03 PM, Raul Miller <
> > > > rauldmil...@gmail.com>
> > > > > > wrote:
> > > > > > > >
> > > > > > > >> I imagine they'd go something like this:
> > > > > > > >>
> > > > > > > >>    X=. a*((sin P) */ cos T)
> > > > > > > >>    Y=. b*(((sin P) */ sin T)
> > > > > > > >>    Z=. c*((cos P) +/ T*0)%2
> > > > > > > >>
> > > > > > > >> The assumption would be that when they are omitted they are 1.
> > > > > > > >>
> > > > > > > >> The trick is recognizing how these parametric equations
> > > > correspond to
> > > > > > > >> your original expression.
> > > > > > > >>
> > > > > > > >> Thanks,
> > > > > > > >>
> > > > > > > >> --
> > > > > > > >> Raul
> > > > > > > >>
> > > > > > > >> On Sat, Mar 7, 2015 at 12:00 AM, Skip Cave <
> > > > s...@caveconsulting.com>
> > > > > > > >> wrote:
> > > > > > > >> > Ok now I'm confused. Nowhere do I see where we set the
> > length
> > > > of the
> > > > > > > >> three
> > > > > > > >> > axes a, b, and c. Also the step verb has lots of variables
> > in
> > > > it,
> > > > > > like a,
> > > > > > > >> > w, n, and z that I don't see defined anywhere.
> > > > > > > >> > steps=: 3 : 'a+(w)*(i.n+1)%n[w=.z-a[''a z n''=.y'
> > > > > > > >> >
> > > > > > > >> > How do I change the lengths of the axes a, b,and c?
> > > > > > > >> >
> > > > > > > >> > Skip Cave
> > > > > > > >> > Cave Consulting LLC
> > > > > > > >> >
> > > > > > > >> > On Fri, Mar 6, 2015 at 10:25 PM, Joe Bogner <
> > > > joebog...@gmail.com>
> > > > > > wrote:
> > > > > > > >> >
> > > > > > > >> >> I don't know what I'm doing other than copy/pasting, but
> > the
> > > > > > example
> > > > > > > >> from
> > > > > > > >> >> the plot demo looks pretty close:
> > > > > > > >> >>
> > > > > > > >> >> load 'plot'
> > > > > > > >> >> pd 'clear'
> > > > > > > >> >> steps=: 3 : 'a+(w)*(i.n+1)%n[w=.z-a[''a z n''=.y'
> > > > > > > >> >> P=. steps 0 1p1 30
> > > > > > > >> >> T=. steps 0 2p1 40
> > > > > > > >> >> X=. ((sin P) */ cos T)
> > > > > > > >> >> Y=. ((sin P) */ sin T)
> > > > > > > >> >> Z=. ((cos P) +/ T*0)%2
> > > > > > > >> >>
> > > > > > > >> >> pd 'backcolor blue'
> > > > > > > >> >> pd 'new 0 0 1000 1000'
> > > > > > > >> >>
> > > > > > > >> >> pd 'type surface'
> > > > > > > >> >> pd 'viewpoint 2 2 2;color grayscale'
> > > > > > > >> >> pd X;Y;Z
> > > > > > > >> >> pd 'show'
> > > > > > > >> >>
> > > > > > > >> >>
> > > > > > > >> >>
> > > > > > > >> >> On Fri, Mar 6, 2015 at 11:18 PM, Raul Miller <
> > > > > > rauldmil...@gmail.com>
> > > > > > > >> >> wrote:
> > > > > > > >> >>
> > > > > > > >> >> > This is something of an aside - I don't know what I'm
> > doing
> > > > yet,
> > > > > > well
> > > > > > > >> >> > enough to implement this via jhs, but here's an
> > ellipsoid:
> > > > > > > >> >> >
> > > > > > > >> >> > https://www.shadertoy.com/view/XtlGDX
> > > > > > > >> >> >
> > > > > > > >> >> > You can tweak the a, b, and c radius values near the top
> > of
> > > > the
> > > > > > script
> > > > > > > >> >> > (which should display on the right side of the screen)
> > and
> > > > hit
> > > > > > the
> > > > > > > >> >> > play button to see the change.
> > > > > > > >> >> >
> > > > > > > >> >> > Thanks,
> > > > > > > >> >> >
> > > > > > > >> >> > --
> > > > > > > >> >> > Raul
> > > > > > > >> >> >
> > > > > > > >> >> > On Fri, Mar 6, 2015 at 10:38 PM, Skip Cave <
> > > > > > s...@caveconsulting.com>
> > > > > > > >> >> > wrote:
> > > > > > > >> >> > > Looking a bit better, but no cigar:
> > > > > > > >> >> > >
> > > > > > > >> >> > > a=:3[b=:3[c=:3
> > > > > > > >> >> > >
> > > > > > > >> >> > >  X=:4 :0
> > > > > > > >> >> > >
> > > > > > > >> >> > > a*(cos x)*cos y
> > > > > > > >> >> > >
> > > > > > > >> >> > > )
> > > > > > > >> >> > >
> > > > > > > >> >> > >  Y=:4 :0
> > > > > > > >> >> > >
> > > > > > > >> >> > > b*(cos x)*sin y
> > > > > > > >> >> > >
> > > > > > > >> >> > > )
> > > > > > > >> >> > >
> > > > > > > >> >> > >  Z=:3 :0
> > > > > > > >> >> > >
> > > > > > > >> >> > > c*(sin y)
> > > > > > > >> >> > >
> > > > > > > >> >> > > )
> > > > > > > >> >> > >
> > > > > > > >> >> > > steps=: 3 : 'a+(w)*(i.n+1)%n[w=.z-a[''a z n''=.y'
> > > > > > > >> >> > >
> > > > > > > >> >> > > draw=:3 :0
> > > > > > > >> >> > >
> > > > > > > >> >> > > angles=: steps _1p1 1p1 100
> > > > > > > >> >> > >
> > > > > > > >> >> > > uangles =: steps _1.5708 1.5708 100
> > > > > > > >> >> > >
> > > > > > > >> >> > > x=. uangles X"0 _ angles
> > > > > > > >> >> > >
> > > > > > > >> >> > > y=. uangles Y"0 _ angles
> > > > > > > >> >> > >
> > > > > > > >> >> > > z=. Z uangles
> > > > > > > >> >> > >
> > > > > > > >> >> > > 'surface' plot x;y;z
> > > > > > > >> >> > >
> > > > > > > >> >> > > )
> > > > > > > >> >> > >
> > > > > > > >> >> > >  draw''
> > > > > > > >> >> > >
> > > > > > > >> >> > >
> > > > > > > >> >> > > output at: http://bit.ly/1wNlQe3
> > > > > > > >> >> > >
> > > > > > > >> >> > >
> > > > > > > >> >> > > Skip Cave
> > > > > > > >> >> > > Cave Consulting LLC
> > > > > > > >> >> > >
> > > > > > > >> >> > > On Fri, Mar 6, 2015 at 9:18 PM, Raul Miller <
> > > > > > rauldmil...@gmail.com>
> > > > > > > >> >> > wrote:
> > > > > > > >> >> > >
> > > > > > > >> >> > >> steps=: 3 : 'a+(w)*(i.n+1)%n[w=.z-a[''a z n''=.y'
> > > > > > > >> >> > >>
> > > > > > > >> >> > >> Thanks,
> > > > > > > >> >> > >>
> > > > > > > >> >> > >> --
> > > > > > > >> >> > >> Raul
> > > > > > > >> >> > >>
> > > > > > > >> >> > >> On Fri, Mar 6, 2015 at 10:08 PM, Skip Cave <
> > > > > > > >> s...@caveconsulting.com>
> > > > > > > >> >> > >> wrote:
> > > > > > > >> >> > >> > Here's what I got whaen I ran Jon's code:
> > > > > > > >> >> > >> >
> > > > > > > >> >> > >> > a=:3[b=:3[c=:3
> > > > > > > >> >> > >> >
> > > > > > > >> >> > >> >  X=:4 :0
> > > > > > > >> >> > >> >
> > > > > > > >> >> > >> > a*(cos x)*cos y
> > > > > > > >> >> > >> >
> > > > > > > >> >> > >> > )
> > > > > > > >> >> > >> >
> > > > > > > >> >> > >> >  Y=:4 :0
> > > > > > > >> >> > >> >
> > > > > > > >> >> > >> > b*(cos x)*sin y
> > > > > > > >> >> > >> >
> > > > > > > >> >> > >> > )
> > > > > > > >> >> > >> >
> > > > > > > >> >> > >> >  Z=:3 :0
> > > > > > > >> >> > >> >
> > > > > > > >> >> > >> > c*(sin y)
> > > > > > > >> >> > >> >
> > > > > > > >> >> > >> > )
> > > > > > > >> >> > >> >
> > > > > > > >> >> > >> >  draw=:3 :0
> > > > > > > >> >> > >> >
> > > > > > > >> >> > >> > angles=: steps _1p1 1p1 100
> > > > > > > >> >> > >> >
> > > > > > > >> >> > >> > uangles =: steps _1.5708 1.5708 100
> > > > > > > >> >> > >> >
> > > > > > > >> >> > >> > x=. uangles X"0 _ angles
> > > > > > > >> >> > >> >
> > > > > > > >> >> > >> > y=. uangles Y"0 _ angles
> > > > > > > >> >> > >> >
> > > > > > > >> >> > >> > z=. Z uangles
> > > > > > > >> >> > >> >
> > > > > > > >> >> > >> > 'surface' plot x;y;z
> > > > > > > >> >> > >> >
> > > > > > > >> >> > >> > )
> > > > > > > >> >> > >> >
> > > > > > > >> >> > >> >  draw''
> > > > > > > >> >> > >> >
> > > > > > > >> >> > >> > |value error: steps
> > > > > > > >> >> > >> >
> > > > > > > >> >> > >> > | angles=: steps _3.14159 3.14159 100
> > > > > > > >> >> > >> >
> > > > > > > >> >> > >> >
> > > > > > > >> >> > >> > Skip Cave
> > > > > > > >> >> > >> > Cave Consulting LLC
> > > > > > > >> >> > >> >
> > > > > > > >> >> > >> > On Fri, Mar 6, 2015 at 8:56 PM, Jon Hough <
> > > > > > jgho...@outlook.com>
> > > > > > > >> >> > wrote:
> > > > > > > >> >> > >> >
> > > > > > > >> >> > >> >>
> > > > > > > >> >> > >> >> I butchered Raul's script slightly. But the
> > resulting
> > > > > > graph is
> > > > > > > >> >> still
> > > > > > > >> >> > >> >> weird. Not sure if it's an improvement.
> > > > > > > >> >> > >> >>
> > > > > > > >> >> > >> >>
> > > > > > > >> >> > >> >> a=:3[b=:3[c=:3
> > > > > > > >> >> > >> >>
> > > > > > > >> >> > >> >>
> > > > > > > >> >> > >> >>
> > > > > > > >> >> > >> >> X=:4 :0
> > > > > > > >> >> > >> >>
> > > > > > > >> >> > >> >>
> > > > > > > >> >> > >> >>
> > > > > > > >> >> > >> >>   a*(cos x)*cos y
> > > > > > > >> >> > >> >>
> > > > > > > >> >> > >> >>
> > > > > > > >> >> > >> >>
> > > > > > > >> >> > >> >> )
> > > > > > > >> >> > >> >>
> > > > > > > >> >> > >> >>
> > > > > > > >> >> > >> >>
> > > > > > > >> >> > >> >>
> > > > > > > >> >> > >> >>
> > > > > > > >> >> > >> >>
> > > > > > > >> >> > >> >> Y=:4 :0
> > > > > > > >> >> > >> >>
> > > > > > > >> >> > >> >>
> > > > > > > >> >> > >> >>
> > > > > > > >> >> > >> >>   b*(cos x)*sin y
> > > > > > > >> >> > >> >>
> > > > > > > >> >> > >> >>
> > > > > > > >> >> > >> >>
> > > > > > > >> >> > >> >> )
> > > > > > > >> >> > >> >>
> > > > > > > >> >> > >> >>
> > > > > > > >> >> > >> >>
> > > > > > > >> >> > >> >>
> > > > > > > >> >> > >> >>
> > > > > > > >> >> > >> >>
> > > > > > > >> >> > >> >> Z=:3 :0
> > > > > > > >> >> > >> >>
> > > > > > > >> >> > >> >>
> > > > > > > >> >> > >> >>
> > > > > > > >> >> > >> >> c*(sin y)
> > > > > > > >> >> > >> >>
> > > > > > > >> >> > >> >>
> > > > > > > >> >> > >> >>
> > > > > > > >> >> > >> >> )
> > > > > > > >> >> > >> >>
> > > > > > > >> >> > >> >>
> > > > > > > >> >> > >> >>
> > > > > > > >> >> > >> >>
> > > > > > > >> >> > >> >>
> > > > > > > >> >> > >> >>
> > > > > > > >> >> > >> >> draw=:3 :0
> > > > > > > >> >> > >> >>
> > > > > > > >> >> > >> >>
> > > > > > > >> >> > >> >>
> > > > > > > >> >> > >> >>   angles=: steps _1p1 1p1 100
> > > > > > > >> >> > >> >>
> > > > > > > >> >> > >> >>
> > > > > > > >> >> > >> >>
> > > > > > > >> >> > >> >>   uangles =: steps _1.5708 1.5708 100
> > > > > > > >> >> > >> >>
> > > > > > > >> >> > >> >>
> > > > > > > >> >> > >> >>
> > > > > > > >> >> > >> >>   x=. uangles X"0 _ angles
> > > > > > > >> >> > >> >>
> > > > > > > >> >> > >> >>
> > > > > > > >> >> > >> >>
> > > > > > > >> >> > >> >>   y=. uangles Y"0 _ angles
> > > > > > > >> >> > >> >>
> > > > > > > >> >> > >> >>
> > > > > > > >> >> > >> >>
> > > > > > > >> >> > >> >>
> > > > > > > >> >> > >> >>
> > > > > > > >> >> > >> >> z=.  Z uangles
> > > > > > > >> >> > >> >>
> > > > > > > >> >> > >> >>
> > > > > > > >> >> > >> >>
> > > > > > > >> >> > >> >>   'surface' plot x;y;z
> > > > > > > >> >> > >> >>
> > > > > > > >> >> > >> >>
> > > > > > > >> >> > >> >>
> > > > > > > >> >> > >> >> )
> > > > > > > >> >> > >> >>
> > > > > > > >> >> > >> >>
> > > > > > > >> >> > >> >>
> > > > > > > >> >> > >> >>
> > > > > > > >> >> > >> >> draw''
> > > > > > > >> >> > >> >>
> > > > > > > >> >> > >> >> > From: jgho...@outlook.com
> > > > > > > >> >> > >> >> > To: programm...@jsoftware.com
> > > > > > > >> >> > >> >> > Date: Sat, 7 Mar 2015 02:46:35 +0000
> > > > > > > >> >> > >> >> > Subject: Re: [Jprogramming] Plotting a 3D Ellipse
> > > > > > > >> >> > >> >> >
> > > > > > > >> >> > >> >> > It seems you are using [-pi,pi] as the range of
> > all
> > > > your
> > > > > > > >> angles.I
> > > > > > > >> >> > >> think
> > > > > > > >> >> > >> >> you need to use [-pi/2,pi/2] as the range for the u
> > > > > > argument (in
> > > > > > > >> >> the
> > > > > > > >> >> > >> >> wikipedia page).
> > > > > > > >> >> > >> >> >
> > > > > > > >> >> > >> >> > > From: rauldmil...@gmail.com
> > > > > > > >> >> > >> >> > > Date: Fri, 6 Mar 2015 21:35:37 -0500
> > > > > > > >> >> > >> >> > > To: programm...@jsoftware.com
> > > > > > > >> >> > >> >> > > Subject: Re: [Jprogramming] Plotting a 3D
> > Ellipse
> > > > > > > >> >> > >> >> > >
> > > > > > > >> >> > >> >> > > Hmm...
> > > > > > > >> >> > >> >> > >
> > > > > > > >> >> > >> >> > > I notice that load'graph' no longer provides
> > the
> > > > steps
> > > > > > verb
> > > > > > > >> >> > >> mentioned
> > > > > > > >> >> > >> >> > > in
> > http://www.jsoftware.com/books/pdf/expmath.pdf
> > > > > > > >> >> > >> >> > >
> > > > > > > >> >> > >> >> > > So here's a workalike:
> > > > > > > >> >> > >> >> > >    steps=: 3 : 'a+(w)*(i.n+1)%n[w=.z-a[''a z
> > > > n''=.y'
> > > > > > > >> >> > >> >> > >
> > > > > > > >> >> > >> >> > > and that gives us an example of a surface plot.
> > > > > > > >> >> > >> >> > >
> > > > > > > >> >> > >> >> > > Next, we need a parametric representation of
> > the
> > > > > > ellipse,
> > > > > > > >> and
> > > > > > > >> >> > >> >> > >
> > > > > > http://en.wikipedia.org/wiki/Ellipsoid#Parameterization
> > > > > > > >> looks
> > > > > > > >> >> > like
> > > > > > > >> >> > >> a
> > > > > > > >> >> > >> >> > > plausible approach there.
> > > > > > > >> >> > >> >> > >
> > > > > > > >> >> > >> >> > > Using that, and
> > > > > > > >> >> http://www.jsoftware.com/help/jforc/graphics.htm
> > > > > > > >> >> > >> as a
> > > > > > > >> >> > >> >> > > starting point, it seems to me that I ought to
> > be
> > > > able
> > > > > > to
> > > > > > > >> draw
> > > > > > > >> >> an
> > > > > > > >> >> > >> >> > > ellipse like this:
> > > > > > > >> >> > >> >> > >
> > > > > > > >> >> > >> >> > > a=:3[b=:4[c=:5
> > > > > > > >> >> > >> >> > >
> > > > > > > >> >> > >> >> > > X=:4 :0~
> > > > > > > >> >> > >> >> > >   a*(cos x)*/cos y
> > > > > > > >> >> > >> >> > > )
> > > > > > > >> >> > >> >> > >
> > > > > > > >> >> > >> >> > > Y=:4 :0~
> > > > > > > >> >> > >> >> > >   b*(cos x)*/sin y
> > > > > > > >> >> > >> >> > > )
> > > > > > > >> >> > >> >> > >
> > > > > > > >> >> > >> >> > > Z=:4 :0~
> > > > > > > >> >> > >> >> > >   c*(sin x)*/1: y
> > > > > > > >> >> > >> >> > > )
> > > > > > > >> >> > >> >> > >
> > > > > > > >> >> > >> >> > > draw=:3 :0
> > > > > > > >> >> > >> >> > >   angles=: steps _1p1 1p1 100
> > > > > > > >> >> > >> >> > >   x=. X angles
> > > > > > > >> >> > >> >> > >   y=. Y angles
> > > > > > > >> >> > >> >> > >   z=. Z angles
> > > > > > > >> >> > >> >> > >   'surface' plot x;y;z
> > > > > > > >> >> > >> >> > > )
> > > > > > > >> >> > >> >> > >
> > > > > > > >> >> > >> >> > > draw''
> > > > > > > >> >> > >> >> > >
> > > > > > > >> >> > >> >> > > Sadly, that's not an ellipse.
> > > > > > > >> >> > >> >> > >
> > > > > > > >> >> > >> >> > > But I do not have enough familiarity with plot
> > to
> > > > know
> > > > > > > >> whether
> > > > > > > >> >> > I've
> > > > > > > >> >> > >> >> > > screwed up my math or if there's a defect in
> > plot
> > > > -- I
> > > > > > don't
> > > > > > > >> >> know
> > > > > > > >> >> > >> how
> > > > > > > >> >> > >> >> > > to isolate the problem.
> > > > > > > >> >> > >> >> > >
> > > > > > > >> >> > >> >> > > That said, a quick test with a 3d model of a
> > cube:
> > > > > > > >> >> > >> >> > >
> > > > > > > >> >> > >> >> > >    'surface' plot ;/|:#:i.8
> > > > > > > >> >> > >> >> > > |NaN error: ncile
> > > > > > > >> >> > >> >> > >
> > > > > > > >> >> > >> >> > > ...suggests that plot isn't really designed to
> > > > > > represent 3d
> > > > > > > >> >> > solids.
> > > > > > > >> >> > >> >> > >
> > > > > > > >> >> > >> >> > > Still, that does not eliminate any potential
> > > > errors on
> > > > > > my
> > > > > > > >> part.
> > > > > > > >> >> > >> >> > >
> > > > > > > >> >> > >> >> > > On the other hand, maybe the right approach
> > would
> > > > be
> > > > > > to use
> > > > > > > >> jhs
> > > > > > > >> >> > and
> > > > > > > >> >> > >> >> > > generate a distance field renderer along the
> > lines
> > > > of
> > > > > > what
> > > > > > > >> you
> > > > > > > >> >> > see
> > > > > > > >> >> > >> at
> > > > > > > >> >> > >> >> > > shadertoy.com.
> > > > > > > >> >> > >> >> > >
> > > > > > > >> >> > >> >> > > I'll have to think a bit to see if I can pull
> > off
> > > > > > something
> > > > > > > >> >> like
> > > > > > > >> >> > >> that.
> > > > > > > >> >> > >> >> > > (I think that that would only work for people
> > who
> > > > have
> > > > > > > >> adequate
> > > > > > > >> >> > >> >> > > graphics hardware support. But I think you
> > have a
> > > > > > suitable
> > > > > > > >> >> > graphics
> > > > > > > >> >> > >> >> > > card?)
> > > > > > > >> >> > >> >> > >
> > > > > > > >> >> > >> >> > > Thanks,
> > > > > > > >> >> > >> >> > >
> > > > > > > >> >> > >> >> > > --
> > > > > > > >> >> > >> >> > > Raul
> > > > > > > >> >> > >> >> > >
> > > > > > > >> >> > >> >> > >
> > > > > > > >> >> > >> >> > > On Fri, Mar 6, 2015 at 7:10 PM, Skip Cave <
> > > > > > > >> >> > s...@caveconsulting.com>
> > > > > > > >> >> > >> >> wrote:
> > > > > > > >> >> > >> >> > > > I want to plot a 3D ellipse (ellipsoid) and
> > then
> > > > be
> > > > > > able
> > > > > > > >> to
> > > > > > > >> >> > change
> > > > > > > >> >> > >> >> the
> > > > > > > >> >> > >> >> > > > lengths of the three axes. The equation of an
> > > > > > ellipse with
> > > > > > > >> >> axis
> > > > > > > >> >> > >> >> lengths of
> > > > > > > >> >> > >> >> > > > a, b, & c is:
> > > > > > > >> >> > >> >> > > >
> > > > > > > >> >> > >> >> > > >  ((x^2)%(a^2)) + ((y^2)%(b^2)) +
> > ((z^2)%(c^2)) =
> > > > 1
> > > > > > > >> >> > >> >> > > >
> > > > > > > >> >> > >> >> > > > How can I arrange this so it can be plotted
> > in a
> > > > 3-D
> > > > > > plot
> > > > > > > >> in
> > > > > > > >> >> J,
> > > > > > > >> >> > >> and
> > > > > > > >> >> > >> >> then be
> > > > > > > >> >> > >> >> > > > able to  experiment with the lengths of the
> > axes?
> > > > > > > >> >> > >> >> > > >
> > > > > > > >> >> > >> >> > > > Skip
> > > > > > > >> >> > >> >> > > >
> > > > > > > >> >> > >> >> > > > Skip Cave
> > > > > > > >> >> > >> >> > > > Cave Consulting LLC
> > > > > > > >> >> > >> >> > > >
> > > > > > > >> >> > >> >>
> > > > > > > >> >> >
> > > > > >
> > ----------------------------------------------------------------------
> > > > > > > >> >> > >> >> > > > For information about J forums see
> > > > > > > >> >> > >> >> http://www.jsoftware.com/forums.htm
> > > > > > > >> >> > >> >> > >
> > > > > > > >> >> > >>
> > > > > > > >>
> > > > ----------------------------------------------------------------------
> > > > > > > >> >> > >> >> > > For information about J forums see
> > > > > > > >> >> > >> http://www.jsoftware.com/forums.htm
> > > > > > > >> >> > >> >> >
> > > > > > > >> >> > >> >> >
> > > > > > > >> >> >
> > > > > >
> > ----------------------------------------------------------------------
> > > > > > > >> >> > >> >> > For information about J forums see
> > > > > > > >> >> > >> http://www.jsoftware.com/forums.htm
> > > > > > > >> >> > >> >>
> > > > > > > >> >> > >> >>
> > > > > > > >> >> >
> > > > > >
> > ----------------------------------------------------------------------
> > > > > > > >> >> > >> >> For information about J forums see
> > > > > > > >> >> > http://www.jsoftware.com/forums.htm
> > > > > > > >> >> > >> >>
> > > > > > > >> >> > >> >
> > > > > > > >> >>
> > > > > >
> > ----------------------------------------------------------------------
> > > > > > > >> >> > >> > For information about J forums see
> > > > > > > >> >> > http://www.jsoftware.com/forums.htm
> > > > > > > >> >> > >>
> > > > > > > >>
> > > > ----------------------------------------------------------------------
> > > > > > > >> >> > >> For information about J forums see
> > > > > > > >> >> http://www.jsoftware.com/forums.htm
> > > > > > > >> >> > >>
> > > > > > > >> >> > >
> > > > > > > >>
> > > > ----------------------------------------------------------------------
> > > > > > > >> >> > > For information about J forums see
> > > > > > > >> http://www.jsoftware.com/forums.htm
> > > > > > > >> >> >
> > > > > >
> > ----------------------------------------------------------------------
> > > > > > > >> >> > For information about J forums see
> > > > > > > >> http://www.jsoftware.com/forums.htm
> > > > > > > >> >> >
> > > > > > > >> >>
> > > > > >
> > ----------------------------------------------------------------------
> > > > > > > >> >> For information about J forums see
> > > > > > http://www.jsoftware.com/forums.htm
> > > > > > > >> >>
> > > > > > > >> >
> > > > > >
> > ----------------------------------------------------------------------
> > > > > > > >> > For information about J forums see
> > > > > > http://www.jsoftware.com/forums.htm
> > > > > > > >>
> > > > ----------------------------------------------------------------------
> > > > > > > >> For information about J forums see
> > > > > > http://www.jsoftware.com/forums.htm
> > > > > > > >>
> > > > > > > >
> > > > ----------------------------------------------------------------------
> > > > > > > > For information about J forums see
> > > > http://www.jsoftware.com/forums.htm
> > > > > > >
> > > > ----------------------------------------------------------------------
> > > > > > > For information about J forums see
> > > > http://www.jsoftware.com/forums.htm
> > > > > >
> > > > >
> > ----------------------------------------------------------------------
> > > > > For information about J forums see
> > http://www.jsoftware.com/forums.htm
> > > >
> > > > ----------------------------------------------------------------------
> > > > For information about J forums see http://www.jsoftware.com/forums.htm
> > > >
> > > ----------------------------------------------------------------------
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> >
> > ----------------------------------------------------------------------
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> >
> ----------------------------------------------------------------------
> For information about J forums see http://www.jsoftware.com/forums.htm
                                          
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