# Difference between revisions of "Field:Fractals"

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===Fractal (Non Integer) Dimension=== | ===Fractal (Non Integer) Dimension=== | ||

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Fractals are too irregular to be defined by traditional or Euclidean geometry language. Objects that can be described by Euclidean geometric dimensions include a line (1 dimension), an square (2 dimension), and a cube (3 dimension). Fractals are instead described by what is called Hausdorff or [[Fractal Dimension|fractal dimension]] that measures how fully a fractal seems to fill space. For example, going back to the coastline example above, the coastline of Norway has an estimated fractal dimension of about 1.52 so it is not quite a line, but not quite an area either. | Fractals are too irregular to be defined by traditional or Euclidean geometry language. Objects that can be described by Euclidean geometric dimensions include a line (1 dimension), an square (2 dimension), and a cube (3 dimension). Fractals are instead described by what is called Hausdorff or [[Fractal Dimension|fractal dimension]] that measures how fully a fractal seems to fill space. For example, going back to the coastline example above, the coastline of Norway has an estimated fractal dimension of about 1.52 so it is not quite a line, but not quite an area either. | ||

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===Recursive=== | ===Recursive=== | ||

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A fractal must have a recursive definition, meaning that the fractal is defined in terms of itself. Fractals can be described by a single equation or by a system of equations, and created by taking an initial starting value and applying the recursive equation(s) to that value over and over again (a process called '''iteration'''). This iteration takes the output calculated from the previous iteration as the input for the next statement. Similarly, if the recursive definition of a fractal is a process, that process is first applied to the starting geometric shape and then continuously iterated to the segments resulting from the previous iteration. Recursive can be seen as a kind of positive feedback loop, where the same definition is applied infinitely by using the results from the previous iteration to start the next iteration. | A fractal must have a recursive definition, meaning that the fractal is defined in terms of itself. Fractals can be described by a single equation or by a system of equations, and created by taking an initial starting value and applying the recursive equation(s) to that value over and over again (a process called '''iteration'''). This iteration takes the output calculated from the previous iteration as the input for the next statement. Similarly, if the recursive definition of a fractal is a process, that process is first applied to the starting geometric shape and then continuously iterated to the segments resulting from the previous iteration. Recursive can be seen as a kind of positive feedback loop, where the same definition is applied infinitely by using the results from the previous iteration to start the next iteration. | ||

Click here to learn more about [[Iterated Functions]]. | Click here to learn more about [[Iterated Functions]]. | ||

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Image:Anna1.jpg|Julia Set (''Escape-Time Fractal'') | Image:Anna1.jpg|Julia Set (''Escape-Time Fractal'') | ||

</gallery> | </gallery> | ||

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+ | == Types of Fractals == | ||

There are four main types of fractals that are categorized by how they are generated. In addition, numerous fractals occur naturally in lightening, broccoli, blood vessels, landscapes, and other phenomena. | There are four main types of fractals that are categorized by how they are generated. In addition, numerous fractals occur naturally in lightening, broccoli, blood vessels, landscapes, and other phenomena. | ||

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− | + | ===Strange attractors=== | |

::Fractals that are considered strange [[Attractors|attractors]] are generated from a set of functions called attractor maps or systems. These systems are [[Chaos|chaotic]] and [[Dynamical Systems|dynamic]]. Initially, the functions appear to map points in a seemingly random order, but the points are in fact over time evolving towards a recognizable structure called an '''attractor''' (because it "attracts" the points into a certain shape). | ::Fractals that are considered strange [[Attractors|attractors]] are generated from a set of functions called attractor maps or systems. These systems are [[Chaos|chaotic]] and [[Dynamical Systems|dynamic]]. Initially, the functions appear to map points in a seemingly random order, but the points are in fact over time evolving towards a recognizable structure called an '''attractor''' (because it "attracts" the points into a certain shape). | ||

::*Examples include: [[Lorenz Attractor]], [[Henon Attractor]], [[Cantor Set]] , and [[Rossler Attractor]]. | ::*Examples include: [[Lorenz Attractor]], [[Henon Attractor]], [[Cantor Set]] , and [[Rossler Attractor]]. | ||

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+ | ===Random fractals=== | ||

::These fractals are created through stochastic methods, meaning that the behavior of these fractals depend on a random factor and usually probability restraints. One way to differentiate between chaotic and random fractals is to observe that chaotic fractals have errors (the difference between one plotted value to the next) that grow exponentially, while random fractal errors are simply random. | ::These fractals are created through stochastic methods, meaning that the behavior of these fractals depend on a random factor and usually probability restraints. One way to differentiate between chaotic and random fractals is to observe that chaotic fractals have errors (the difference between one plotted value to the next) that grow exponentially, while random fractal errors are simply random. | ||

::*Examples include: [[Levy Flights]], [[Brownian Motion]], [[Brownian Tree]], and fractal landscapes. | ::*Examples include: [[Levy Flights]], [[Brownian Motion]], [[Brownian Tree]], and fractal landscapes. | ||

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− | + | ===Escape-time (orbit) fractals=== | |

::Escape-time fractals are created in the complex plane with a single function, some <math>f(z)</math>, where ''z'' is a [[Complex Numbers|complex number]]. On a computer, each pixel corresponds to a complex number value. Each complex number value is applied recursively to the function until it reaches infinity or until it is clear that value will converge to zero. A color is assigned to each complex number value or pixel: the pixel is either colored black if the value converges to zero or the pixel is given a color based on the number of iterations (aka. '''escape time''') it took for the value to reach infinity. The intermediary numbers that arise from the iterations are referred to as their '''orbit'''. The boundary between black and color pixels is infinite and increasingly complex. | ::Escape-time fractals are created in the complex plane with a single function, some <math>f(z)</math>, where ''z'' is a [[Complex Numbers|complex number]]. On a computer, each pixel corresponds to a complex number value. Each complex number value is applied recursively to the function until it reaches infinity or until it is clear that value will converge to zero. A color is assigned to each complex number value or pixel: the pixel is either colored black if the value converges to zero or the pixel is given a color based on the number of iterations (aka. '''escape time''') it took for the value to reach infinity. The intermediary numbers that arise from the iterations are referred to as their '''orbit'''. The boundary between black and color pixels is infinite and increasingly complex. | ||

::*Examples include: [[Mandelbrot Set]], [[Julia Sets]], and [[Lyapunov Fractal]]. | ::*Examples include: [[Mandelbrot Set]], [[Julia Sets]], and [[Lyapunov Fractal]]. | ||

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## Revision as of 09:49, 25 July 2011

# Fractals

A fractal is often defined as a geometric shape that is **self-similar**, that is, whose magnified parts look like a smaller copy of the whole. The term "fractal" was coined by Benoit Mandelbolt in 1975 from the latin term *fractus* meaning "fragmented" or "irregular".

This concept can be explained in a commonly used analogy involving the coastline of an island:

*Suppose you wanted to measure the total perimeter of an island. You could begin by roughly estimating the perimeter of the island by measuring the border of the island from a high vantage point like an airplane and using miles as units. Next, to be more accurate, you could walk along the island's borders and measure around its various coves and bays using a measuring tape and foot as units. Then, if you wanted to be really accurate, you could carefully measure around every single protruding rock and detail of the island with foot-long ruler and use inches as a measuring unit.*

The perimeter of the island would grow as you decrease the size of your measuring device and increase the accuracy of your measurements. Also, the island would more or less self-similar (in terms of becoming more and more jagged and complex) as you continued to shorten your measuring device.

## Contents |
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## References

Wikipedia, Fractals Page

Cynthia Lanius, Cynthia Lanius' Lessons: A Fractal Lesson

CoolMath.com, Math of Fractals