cKleinhuis


« Reply #15 on: October 23, 2012, 12:51:07 PM » 

@kram sure, this is the reason why i left the hausdorff dimension of the border outside, but they understood that the coastline of britain and mandelbrots border have something in common and i said as well that opposed to the coastline of england the mandelbrot set is infinite between each part ... at least i hope so .... couldnt it be said that anything is fractal which has a higher dimension as the topological dimension !? so, when a line has a hausdorff dimension above 1 it is fractal ?! any counter examples please



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taurus


« Reply #16 on: October 23, 2012, 02:18:54 PM » 

couldnt it be said that anything is fractal which has a higher dimension as the topological dimension !? so, when a line has a hausdorff dimension above 1 it is fractal ?! any counter examples please Maybe, but there are also fractals with a lower fractal dimension, than the topological one. Menger sponge: 2.727 Sierpinski carpet (antenna): 1.8928 Sierpinski triangle: 1.585



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hobold
Fractal Bachius
Posts: 573


« Reply #17 on: October 23, 2012, 05:41:10 PM » 

Also, I'm not sure, don't quote me on that, but the LorentzAttractor seems fairly smooth to me.
The Lorentz attractor is made of smooth fiber (or fibers?), but those fibers are distributed fractally in space. You can think of it as an extreme example of the whipped cream effect.



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Syntopia


« Reply #18 on: October 24, 2012, 12:04:24 AM » 

Wiki has a nice page on fractal dimensions: http://en.wikipedia.org/wiki/List_of_fractals_by_Hausdorff_dimensionIt seems that many fractals with lower fractal dimension than topological are made by removing parts, and many fractals with higher fractal dimension than the topological are made by folding or twisting the objects (or by adding parts). Then it should be possible to make a fractal with topological dimension equal to the fractal dimension by doing both folding and reductions: for instance by creating a koch surface, but at each step remove parts of each face.



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Syntopia


« Reply #19 on: October 24, 2012, 12:27:25 AM » 

Interesting: on the Wikipediasite the Mandelbulb is listed as having Hausdorff dimension 3, which a link to FractalForums for the derivation: http://www.fractalforums.com/theory/hausdorffdimensionofthemandelbulb/15/I know next to nothing about Hausdorff dimensions, but as I read it, the argumentation is that the Mandelbulb has a crosssection, which is the Power8 (2D) Mandelbrot boundary (which is proven to have Hausdorf dimension 2). Thus in a neighbourhood around the crosssection we must have a 2+1 dimensions (< I'm not sure about this last part  it combines reasoning from Euclidean dimension intuition with fractal dimensions). What bothers me is this: Look at the Menger: It has fractal dimension 2.7268. But each of its faces is a Sierpinski carpet with dimension 1.8928. Using the same logic the Menger should have dimension 2.8929  but it does not.



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cKleinhuis


« Reply #20 on: October 24, 2012, 04:32:26 AM » 

I dont like the link back to frsctalforums at this point as well because it is a too simple desvription ad far as i understand it is is although it has whipped cream the crispy parts make up for it . . .



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kram1032


« Reply #21 on: October 24, 2012, 09:22:50 AM » 

Guys, you should read the very top of the wiki page you just linked. According to Falconer, one of the essential features of a fractal is that its Hausdorff dimension strictly exceeds its topological dimension.^{[1]} Note: The topological dimension is essentially the dimension of the "surface" of an object. Then there's the, I think it's called, geometric dimension, which is essentially the dimension of the lowestintegerdimensional euclidean space it can lie in. For example, a 2Sphere has topological dimension 2 (the dimension of its surface), however, its geometric dimension is 3, since it has to be put into euclidean space. The Hausdorff dimension always lies between those two dimensions. So an object with Hausdorffdimension, say, 0.5, will be something between a set of disconnected points (0Dimensional) and a set of lines (1Dimensional) It will also have a topological dimension of 0 and a geometric dimension of 1. A linesection also has topological dimension 0 (the "surface" of a linesegment is the two end points which are both 0dimensional) and a geometric dimension 1. The Hausdorffdimension in this case is 1 too.



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hobold
Fractal Bachius
Posts: 573


« Reply #22 on: October 24, 2012, 12:36:08 PM » 

The possible range of Hausdorff dimensions for a particular fractal construction is not limited to the interval between adjacent integers. For example fractals made of discrete points (i.e. clouds or dust) can be linefilling (dimension 1), plane filling (dimension 2), space filling (dimension 3), and so on.



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taurus


« Reply #23 on: October 24, 2012, 12:48:58 PM » 

Guys, you should read the very top of the wiki page you just linked.
According to Falconer, one of the essential features of a fractal is that its Hausdorff dimension strictly exceeds its topological dimension.
It starts to get clearer, some way down in wikipedia article I learned, that the SURFACE of the menger sponge has a dimension of 2.727 not the cube itself. so the rule of exceeding hausdoff dimension is not broken. But I still ask myself what dimension has the sponge? no dimension, because the volume is zero? Interresting also the fractal dimension of brain and lung surfaces. Our lung has a fractal surface of almost three dimensions (2.97) Surprisingly high!



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David Makin


« Reply #24 on: October 24, 2012, 01:18:57 PM » 

Personally I would redefine "Fractal" as anything that can be created (or simulated) using fractal techniques  of course that means *everything*  all other geometries are thus special subsets of fractals rather than the other way around. To me this makes more sense than viewing fractals as "special" and other more restrictive geometries as "general".



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David Makin


« Reply #25 on: October 24, 2012, 01:22:16 PM » 

Interresting also the fractal dimension of brain and lung surfaces. Our lung has a fractal surface of almost three dimensions (2.97) Surprisingly high!
Given how efficient evolution is and the fact that the greater the surface area of the lungs the better I don't really think it's that surprising  I'd expect fish gills to have a similar dimension



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Syntopia


« Reply #26 on: October 24, 2012, 01:47:28 PM » 

It starts to get clearer, some way down in wikipedia article I learned, that the SURFACE of the menger sponge has a dimension of 2.727 not the cube itself. so the rule of exceeding hausdoff dimension is not broken. But I still ask myself what dimension has the sponge? no dimension, because the volume is zero?
I think the Wikipedia page says that both the surface and volume fractal dimension is 2.727 (see note at the right of the Mender).



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taurus


« Reply #27 on: October 24, 2012, 02:13:57 PM » 

I think the Wikipedia page says that both the surface and volume fractal dimension is 2.727 (see note at the right of the Mender).
for sure, I should read till the end But what about this definition, that for a fractal the hausdorff dimension "strictly exceeds" topological dimension? I understand "strictly exceeds" as "must be higher". Do I misunderstand?



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hobold
Fractal Bachius
Posts: 573


« Reply #28 on: October 24, 2012, 03:43:32 PM » 

Mathematical jargon:
"exceeds" often means ">=", "strictly exceeds" always means ">" (explicitly excluding the case of being equal).



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taurus


« Reply #29 on: October 24, 2012, 04:09:39 PM » 

Mathematical jargon:
"exceeds" often means ">=", "strictly exceeds" always means ">" (explicitly excluding the case of being equal).
ok. but why does a math professor (Kenneth Falconer) claim, that a fractal's hausdorff dimension "strictly exceeds" its topological dimension, while the mengersponge (and others) contradicts this claim. I doubt that this is a simple mistake  it is too obvious. Or is my assumption for the Mengersponge wrong? topological dim=3 > 2.727=hausdorff dim



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