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From: Tom Melly
Subject: Iso-equation query
Date: 4 May 2001 08:17:33
Message: <3af29ddd$1@news.povray.org>
In a book I'm reading, there is a nice 3d shape which the book says is the
result of the equation:

x^3 + y^3 = 1

However, it comments "x and y are regarded as complex variables".

What does a complex variable mean in this context and what would be the
iso-surface function for the above?

Many thanks in anticipation...

--
"To stop children being afraid of the dark, try to fill their daylight hours
with as much terror as possible"
www.tomandlu.co.uk


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From: Francois Labreque
Subject: Re: Iso-equation query
Date: 4 May 2001 08:48:53
Message: <3AF2A40F.7E249429@videotron.ca>
Tom Melly wrote:
> 
> In a book I'm reading, there is a nice 3d shape which the book says is the
> result of the equation:
> 
> x^3 + y^3 = 1
> 
> However, it comments "x and y are regarded as complex variables".
> 
> What does a complex variable mean in this context

A complex variable is a variable that holds a a number that has the form
"a + bi", where i is an imaginary number defined as sqrt(-1).

> and what would be the
> iso-surface function for the above?

I could be wrong, but I don't think isos work with complex numbers and
since both x and y are two-dimensional values, it makes the function
describe a 4D shape, which I know isos don't understand.

-- 
Francois Labreque | The surest sign of the existence of extra-
    flabreque     | terrestrial intelligence is that they never
        @         | bothered to come down here and visit us!
  videotron.ca    |                             - Calvin


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From: David Fontaine
Subject: Re: Iso-equation query
Date: 4 May 2001 18:34:28
Message: <3AF32D5F.A1E292DD@faricy.net>
Cubic julia fractal?

-- 
David Fontaine  <dav### [at] faricynet>  ICQ 55354965
My raytracing gallery:  http://davidf.faricy.net/


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From: Alberto
Subject: Re: Iso-equation query
Date: 4 May 2001 22:05:44
Message: <3AF35FB8.E9903A83@usb.ve>
Tom Melly wrote:
> 
> In a book I'm reading, there is a nice 3d shape which the book says is the
> result of the equation:
> 
> x^3 + y^3 = 1
> 
> However, it comments "x and y are regarded as complex variables".
> 
> What does a complex variable mean in this context and what would be the
> iso-surface function for the above?
> 
> Many thanks in anticipation...

There is too little information to give you an answer. What I see is a
complex function which depends on four real variables with a real
constraint. I can't imagine how this could be used in a iso-surface. Is
there any other information in your book about how the shape was constructed?
If not, you could contact the author(s) and ask.

Regards, Alberto.


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From: Alberto
Subject: Re: Iso-equation query
Date: 4 May 2001 23:22:15
Message: <3AF371A8.DC10F9BD@usb.ve>
Thinking a little bit further, you can consider that you have a complex
restriction. In this case, your question has many answers. One solution is

 x^3 - 3*x*y^2 - sqrt(3)*z^2*sqrt((-3*x^2*y + y^3 + z^3)/z) + 
  ((-3*x^2*y + y^3 + z^3)/z)^(3/2)/(3*sqrt(3)) = 1

Alberto.


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From: Nekar Xenos
Subject: Re: Iso-equation query
Date: 7 May 2001 03:39:02
Message: <3af65116@news.povray.org>
> I don't think isos work with complex numbers

So you can't do iso-mandelbrots?

Nekar
--
#version unofficial MegaPov 0.7;#local Q=seed(7);#local S=<-2,2,5>;#local
E=<2
,-2,5>;#local B=S;#while(vlength(B-E)>.1)#local
B=(B+(<rand(Q),rand(Q),rand(Q)
>/20));#local B=B-(2*(B-S))*((vlength(B-E)>vlength(S-E)));#local
S=B;glow{//NX
location S size.1 radius.07}glow{location S size.1 radius.07 rotate
z*90}#end


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From: Tom Melly
Subject: Re: Iso-equation query
Date: 8 May 2001 04:31:17
Message: <3af7aed5@news.povray.org>
"Nekar Xenos" <j-p### [at] citywalkcoza> wrote in message
news:3af65116@news.povray.org...
>
> > I don't think isos work with complex numbers
>
> So you can't do iso-mandelbrots?
>

Well, you can't have iterations in an iso. I've wondered if, provided you
were willing to accept a fairly low number of iterations, it would still be
possible by nesting the iterations (which would no longer be iterations).


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From: Chris Huff
Subject: Re: Iso-equation query
Date: 8 May 2001 06:34:48
Message: <3af7cbc7@news.povray.org>
Tom Melly <tom### [at] tomandlucouk> wrote:

> Well, you can't have iterations in an iso. I've wondered if, provided you
> were willing to accept a fairly low number of iterations, it would still be
> possible by nesting the iterations (which would no longer be iterations).

Well, I believe you can trick POV into using recursive functions, you
need to break the recursion using the if() "function". You have to
declare the function as something else first, a completely empty function
will work, then you follow it with a recursive declaration.


-- 
Christopher James Huff - chr### [at] maccom
Home Page: http://homepage.mac.com/chrishuff/
POV-Ray TAG e-mail: chr### [at] povrayorg
POV-Ray TAG web site: http://tag.povray.org/


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From: Tom Melly
Subject: Re: Iso-equation query
Date: 8 May 2001 08:51:49
Message: <3af7ebe5$1@news.povray.org>
"Chris Huff" <chr### [at] maccom> wrote in message
news:3af7cbc7@news.povray.org...
>
> Well, I believe you can trick POV into using recursive functions, you
> need to break the recursion using the if() "function". You have to
> declare the function as something else first, a completely empty function
> will work, then you follow it with a recursive declaration.
>

Can you post a small sample of this?


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From: Vahur Krouverk
Subject: Re: Iso-equation query
Date: 8 May 2001 13:05:43
Message: <3AF82777.39719F7A@comtrade.ee>
Tom Melly wrote:
> 
> "Nekar Xenos" <j-p### [at] citywalkcoza> wrote in message
> news:3af65116@news.povray.org...
> >
> > > I don't think isos work with complex numbers
> >
> > So you can't do iso-mandelbrots?
> >
> 
> Well, you can't have iterations in an iso. I've wondered if, provided you
> were willing to accept a fairly low number of iterations, it would still be
> possible by nesting the iterations (which would no longer be iterations).
If you get last version of POVMan, then you can use specific shader type
iso_function for isosurface potential calculation. Shader language
supports for and while cycles, so it is quite easy write 'recursive'
iso-functions. POVMan documentation contains example of menger sponge,
where you can specify iteration depth by setting shader input parameter
and watch, how sponge disappears...


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