Greg M. Johnson wrote:
> Are you sure?

Sure about what?

> function {noise3d(x ^0.5, y, z)}, I know,  is symmetric about the x=0
> plane.

Because x^.5 actually does (abs( x))^.5
(calling the C function pow(abs(x),.5) )

> function {noise3d(x^3.0, y, z)}, I will bet, behaves correctly, and has
> a kind of symmetry like the curve y=x^3.

Because x^3.0 actually does x*x*x

> There is something "more wrong" here.  If Ron were correct, then x^3
> would also be symmetric about x=0.

Ron didn't claim x^3 was (abs(x))^3. I  prematurely did claim that, and
I was horribly, sorrowfully, and disgustingly mistaken.


> david sharp wrote:
>
> > david sharp <dsh### [at] interportnet> wrote in message
> > news:387a0473@news.povray.org...
> > >
> > > Ron Parker <ron### [at] povrayorg> wrote in message
> > > news:387a0293@news.povray.org...
> > > > On Mon, 10 Jan 2000 10:55:52 -0500, david sharp wrote:
> > > > >The isosurface stuff converts x to absolute value of x
> > > > >before trying to use the ^. This is just to avoid many floating
> > > > >point errors.  The isosurface code does the same conversion
> > > > >before applying sqrt() or ln().
> > > >
> > > > Does it only do that for fractional exponents, or does it also
> > > > do it for odd integer exponents?
> > >
> > > Always.
> >
> > No, not always. (I should have actually checked before replying)
> > there is a ffloor test to distinguish integers from fractions.
>
>
>

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