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| In [[mathematics]] and [[Computability theory (computer science)|computability theory]], an '''elementary cellular automaton''' is a one-dimensional [[cellular automaton]] where there are two possible states (labeled 0 and 1) and the rule to determine the state of a cell in the next generation depends only on the current state of the cell and its two immediate neighbors. As such it is one of the simplest possible models of computation. Nevertheless, there is an elementary cellular automaton ([[rule 110]], defined below) which is capable of [[Turing completeness|universal computation]].
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| ==The numbering system==
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| There are 8 = 2<sup>3</sup> possible configurations for a cell and its two immediate neighbors. The rule defining the cellular automaton must specify the resulting state for each of these possibilities so there are 256 = 2<sup>2<sup>3</sup></sup> possible elementary cellular automata. [[Stephen Wolfram]] proposed a scheme, known as the [[Wolfram code]], to assign each rule a number from 0 to 255 which has become standard. Each possible current configuration is written in order, 111, 110, ..., 001, 000, and the resulting state for each of these configurations is written in the same order and interpreted as the binary representation of an integer. This number is taken to be the rule number of the automaton. For example, 110<sub>d</sub>=96<sub>d</sub>+14<sub>d</sub> written in binary is 01101110<sub>2</sub>. So rule 110 is defined by the transition rule:
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| {| class="wikitable" style="text-align: center"
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| |-
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| | 111
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| | 110
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| | 101
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| | 100
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| | 011
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| | 010
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| | 001
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| | 000
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| ! current pattern
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| ! P=(L,C,R)
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| |-
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| | 0
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| | 1
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| | 1
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| | 0
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| | 1
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| | 1
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| | 1
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| | 0
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| ! new state for center cell
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| ! N<sub>110<sub>d</sub></sub>=(C+R+C*R+L*C*R)%2
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| |}
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| | |
| ==Reflections and complements==
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| Although there are 256 possible rules, many of these are trivially equivalent to each other up to a simple transformation of the underlying geometry. The first such transformation is reflection through a vertical axis and the result of applying this transformation to a given rule is called the '''mirrored rule'''. These rules will exhibit the same behavior up to reflection through a vertical axis, and so are equivalent in a computational sense.
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| For example, if the definition of rule 110 is reflected through a vertical line, the following rule (rule 124) is obtained:
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| {| class="wikitable" style="text-align: center"
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| |-
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| | 111
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| | 110
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| | 101
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| | 100
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| | 011
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| | 010
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| | 001
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| | 000
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| ! current pattern
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| | P=(L,C,R)
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| |-
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| | 0
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| | 1
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| | 1
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| | 1
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| | 1
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| | 1
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| | 0
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| | 0
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| ! new state for center cell
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| | N<sub>112<sub>d</sub>+12<sub>d</sub>=124<sub>d</sub></sub>=(L+C+L*C+L*C*R)%2
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| |}
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| Rules which are the same as their mirrored rule are called '''amphichiral'''. Of the 256 elementary cellular automata, 64 are amphichiral.
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| The second such transformation is to exchange the roles of 0 and 1 in the definition. The result of applying this transformation to a given rule is called the '''complementary rule'''. | |
| For example, if this transformation is applied to rule 110, the following rule (rule 137) obtained:
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| {| class="wikitable" style="text-align: center"
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| |-
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| ! current pattern
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| | 111
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| | 110
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| | 101
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| | 100
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| | 011
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| | 010
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| | 001
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| | 000
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| |-
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| ! new state for center cell
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| | 1
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| | 0
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| | 0
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| | 0
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| | 1
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| | 0
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| | 0
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| | 1
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| |}
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| There are 16 rules which are the same as their complementary rules.
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| Finally, the previous two transformations can be applied successively to a rule to obtain the mirrored complementary rule. For example, the mirrored complementary rule of rule 110 is rule 193. There are 8 rules which are the same as their mirrored complementary rules.
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| Of the 256 elementary cellular automata, there are 88 which are inequivalent under these transformations.
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| ==Single 1 histories==
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| One method used to study these automata is to follow its history with an initial state of all 0s except for a single cell with a 1. When the rule number is even (so that an input of 000 does not compute to a 1) it makes sense to interpret state at each time, ''t'', as an integer expressed in binary, producing a sequence ''a''(''t'') of integers. In many cases these sequences have simple, closed form expressions or have a [[generating function]] with a simple form. The following rules are notable:
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| ===Rule 28===
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| The sequence generated is 1, 3, 5, 11, 21, 43, 85, 171, ... {{OEIS|id=A001045 }}. This is the sequence of [[Jacobsthal numbers]] and has generating function
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| :<math>\frac{1+2x}{(1+x)(1-2x)}</math>.
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| It has the closed form expression
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| :<math>a(t) = (4\cdot 2^t-(-1)^t)/3</math>
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| Note that rule 156 generates the same sequence.
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| ===Rule 50===
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| The sequence generated is 1, 5, 21, 85, 341, 1365, 5461, 21845, ... {{OEIS|id=A002450}}. This has generating function
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| :<math>\frac{1}{(1-x)(1-4x)}</math>.
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| It has the closed form expression
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| :<math>a(t) = (4\cdot 4^t-1)/3</math>.
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| Note that rules 58, 114, 122, 178, 186, 242 and 250 generate the same sequence.
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| ===Rule 54===
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| The sequence generated is 1, 7, 17, 119, 273, 1911, 4369, 30583, ... {{OEIS|id=A118108}}. This has generating function
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| :<math>\frac{1+7x}{(1-x^2)(1-16x^2)}</math>.
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| It has the closed form expression
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| :<math>a(t) = (22\cdot 4^t-6(-4)^t-4+3(-1)^t)/15</math>.
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| ===Rule 60===
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| The sequence generated is 1, 3, 5, 15, 17, 51, 85, 255, ... {{OEIS|id=A001317}}. This can be obtained by taking successive rows of [[Pascal's triangle]] modulo 2 and interpreting them as integers in binary, which can be graphically represented by a [[Sierpinski triangle]].
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| ===Rule 90===
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| {{main|Rule 90}}
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| The sequence generated is 1, 5, 17, 85, 257, 1285, 4369, 21845, ... {{OEIS|id=A038183}}. This can be obtained by taking successive rows of [[Pascal's triangle]] modulo 2 and interpreting them as integers in base 4. Note that rules 18, 26, 82, 146, 154, 210 and 218 generate the same sequence.
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| ===Rule 94===
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| The sequence generated is 1, 7, 27, 119, 427, 1879, 6827, 30039, ... {{OEIS|id=A118101}}. This can be expressed as
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| :<math>a(t) =
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| \begin{cases}
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| 1, & \mbox{if }t = 0 \\
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| 7, & \mbox{if }t = 1 \\
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| (1+5\cdot 4^n)/3 , & \mbox{if }t\mbox{ is even }>0 \\
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| (10+11\cdot 4^n)/6 , & \mbox{if }t\mbox{ is odd }>1
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| \end{cases}
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| </math>.
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| This has generating function
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| :<math>\frac{(1+2x)(1+5x-16x^4)}{(1-x^2)(1-16x^2)}</math>.
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| ===Rule 102===
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| The sequence generated is 1, 6, 20, 120, 272, 1632, 5440, 32640, ... {{OEIS|id=A117998}}. This is simply the sequence generated by rule 60 (which is its mirror rule) multiplied by successive powers of 2.
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| ===Rule 110===
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| {{main|Rule 110}}
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| ===Rule 150===
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| The sequence generated is 1, 7, 21, 107, 273, 1911, 5189, 28123, ... {{OEIS|id=A038184}}. This can be obtained by taking the coefficients of the successive powers of (1+''x''+''x''<sup>2</sup>) modulo 2 and interpreting them as integers in binary.
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| ===Rule 158===
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| The sequence generated is 1, 7, 29, 115, 477, 1843, 7645, 29491, ... {{OEIS|id=A118171}}. This has generating function
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| :<math>\frac{1+7x+12x^2-4x^3}{(1-x^2)(1-16x^2)}</math>.
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| ===Rule 188===
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| The sequence generated is 1, 3, 5, 15, 29, 55, 93, 247, ... {{OEIS|id=A118173}}. This has generating function
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| :<math>\frac{1+3x+4x^2+12x^3+8x^4-8x^5}{(1-x^2)(1-16x^4)}</math>.
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| ===Rule 190===
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| The sequence generated is 1, 7, 29, 119, 477, 1911, 7645, 30583, ... {{OEIS|id=A037576}}. This has generating function
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| :<math>\frac{1+3x}{(1-x^2)(1-4x)}</math>.
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| ===Rule 220===
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| The sequence generated is 1, 3, 7, 15, 31, 63, 127, 255, ... {{OEIS|id=A000225}}. This is the sequence of [[Mersenne numbers]] and has generating function
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| :<math>\frac{1}{(1-x)(1-2x)}</math>.
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| It has the closed form expression
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| :<math>a(t) = 2\cdot 2^t-1</math>.
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| Note that rule 252 generates the same sequence.
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| ===Rule 222===
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| The sequence generated is 1, 7, 31, 127, 511, 2047, 8191, 32767, ... {{OEIS|id=A083420}}. This is every other entry in the sequence of [[Mersenne numbers]] and has generating function
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| :<math>\frac{1+2x}{(1-x)(1-4x)}</math>.
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| It has the closed form expression
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| :<math>a(t) = 2\cdot 4^t-1</math>.
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| Note that rule 254 generates the same sequence.
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| <!--
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| ===Images for rules 0-99===
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| These start with a single pixel.
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| <gallery widths="100px" heights="100px">
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| Image:WolframRule0.png|Rule 0
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| Image:WolframRule1.png|Rule 1
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| Image:WolframRule2.png|Rule 2
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| Image:WolframRule3.png|Rule 3
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| Image:WolframRule4.png|Rule 4
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| Image:WolframRule5.png|Rule 5
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| Image:WolframRule6.png|Rule 6
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| Image:WolframRule7.png|Rule 7
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| Image:WolframRule8.png|Rule 8
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| Image:WolframRule9.png|Rule 9
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| Image:WolframRule10.png|Rule 10
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| Image:WolframRule11.png|Rule 11
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| Image:WolframRule12.png|Rule 12
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| Image:WolframRule13.png|Rule 13
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| Image:WolframRule14.png|Rule 14
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| Image:WolframRule15.png|Rule 15
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| Image:WolframRule16.png|Rule 16
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| Image:WolframRule17.png|Rule 17
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| Image:WolframRule18.png|Rule 18
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| Image:WolframRule19.png|Rule 19
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| Image:WolframRule20.png|Rule 20
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| Image:WolframRule21.png|Rule 21
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| Image:WolframRule22.png|Rule 22
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| Image:WolframRule23.png|Rule 23
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| Image:WolframRule24.png|Rule 24
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| Image:WolframRule25.png|Rule 25
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| Image:WolframRule26.png|Rule 26
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| Image:WolframRule27.png|Rule 27
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| Image:WolframRule28.png|Rule 28
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| Image:WolframRule29.png|Rule 29
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| Image:WolframRule30.png|Rule 30
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| Image:WolframRule31.png|Rule 31
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| Image:WolframRule32.png|Rule 32
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| Image:WolframRule33.png|Rule 33
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| Image:WolframRule34.png|Rule 34
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| Image:WolframRule35.png|Rule 35
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| Image:WolframRule36.png|Rule 36
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| Image:WolframRule37.png|Rule 37
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| Image:WolframRule38.png|Rule 38
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| Image:WolframRule39.png|Rule 39
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| Image:WolframRule40.png|Rule 40
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| Image:WolframRule41.png|Rule 41
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| Image:WolframRule42.png|Rule 42
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| Image:WolframRule43.png|Rule 43
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| Image:WolframRule44.png|Rule 44
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| Image:WolframRule45.png|Rule 45
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| Image:WolframRule46.png|Rule 46
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| Image:WolframRule47.png|Rule 47
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| Image:WolframRule48.png|Rule 48
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| Image:WolframRule49.png|Rule 49
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| Image:WolframRule50.png|Rule 50
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| Image:WolframRule51.png|Rule 51
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| Image:WolframRule52.png|Rule 52
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| Image:WolframRule53.png|Rule 53
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| Image:WolframRule54.png|Rule 54
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| Image:WolframRule55.png|Rule 55
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| Image:WolframRule56.png|Rule 56
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| Image:WolframRule57.png|Rule 57
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| Image:WolframRule58.png|Rule 58
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| Image:WolframRule59.png|Rule 59
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| Image:WolframRule60.png|Rule 60
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| Image:WolframRule61.png|Rule 61
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| Image:WolframRule62.png|Rule 62
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| Image:WolframRule63.png|Rule 63
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| Image:WolframRule64.png|Rule 64
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| Image:WolframRule65.png|Rule 65
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| Image:WolframRule66.png|Rule 66
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| Image:WolframRule67.png|Rule 67
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| Image:WolframRule68.png|Rule 68
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| Image:WolframRule69.png|Rule 69
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| Image:WolframRule70.png|Rule 70
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| Image:WolframRule71.png|Rule 71
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| Image:WolframRule72.png|Rule 72
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| Image:WolframRule73.png|Rule 73
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| Image:WolframRule74.png|Rule 74
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| Image:WolframRule75.png|Rule 75
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| Image:WolframRule76.png|Rule 76
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| Image:WolframRule77.png|Rule 77
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| Image:WolframRule78.png|Rule 78
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| Image:WolframRule79.png|Rule 79
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| Image:WolframRule80.png|Rule 80
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| Image:WolframRule81.png|Rule 81
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| Image:WolframRule82.png|Rule 82
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| Image:WolframRule83.png|Rule 83
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| Image:WolframRule84.png|Rule 84
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| Image:WolframRule85.png|Rule 85
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| Image:WolframRule86.png|Rule 86
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| Image:WolframRule87.png|Rule 87
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| Image:WolframRule88.png|Rule 88
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| Image:WolframRule89.png|Rule 89
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| Image:WolframRule90.png|Rule 90
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| Image:WolframRule91.png|Rule 91
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| Image:WolframRule92.png|Rule 92
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| Image:WolframRule93.png|Rule 93
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| Image:WolframRule94.png|Rule 94
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| Image:WolframRule95.png|Rule 95
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| Image:WolframRule96.png|Rule 96
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| Image:WolframRule97.png|Rule 97
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| Image:WolframRule98.png|Rule 98
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| Image:WolframRule99.png|Rule 99
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| </gallery>
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| -->
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| <!--
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| <gallery widths="100px" heights="100px">
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| Image:WolframRule100.png|Rule 100
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| Image:WolframRule101.png|Rule 101
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| Image:WolframRule102.png|Rule 102
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| Image:WolframRule103.png|Rule 103
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| Image:WolframRule104.png|Rule 104
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| Image:WolframRule105.png|Rule 105
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| Image:WolframRule106.png|Rule 106
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| Image:WolframRule107.png|Rule 107
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| Image:WolframRule108.png|Rule 108
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| Image:WolframRule109.png|Rule 109
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| Image:WolframRule110.png|Rule 110
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| Image:WolframRule111.png|Rule 111
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| Image:WolframRule112.png|Rule 112
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| Image:WolframRule113.png|Rule 113
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| Image:WolframRule114.png|Rule 114
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| Image:WolframRule115.png|Rule 115
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| Image:WolframRule116.png|Rule 116
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| Image:WolframRule117.png|Rule 117
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| Image:WolframRule118.png|Rule 118
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| Image:WolframRule119.png|Rule 119
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| Image:WolframRule120.png|Rule 120
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| Image:WolframRule121.png|Rule 121
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| Image:WolframRule122.png|Rule 122
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| Image:WolframRule123.png|Rule 123
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| Image:WolframRule124.png|Rule 124
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| Image:WolframRule125.png|Rule 125
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| Image:WolframRule126.png|Rule 126
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| Image:WolframRule127.png|Rule 127
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| Image:WolframRule128.png|Rule 128
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| Image:WolframRule129.png|Rule 129
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| Image:WolframRule130.png|Rule 130
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| Image:WolframRule131.png|Rule 131
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| Image:WolframRule132.png|Rule 132
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| Image:WolframRule133.png|Rule 133
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| Image:WolframRule134.png|Rule 134
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| Image:WolframRule135.png|Rule 135
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| Image:WolframRule136.png|Rule 136
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| Image:WolframRule137.png|Rule 137
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| Image:WolframRule138.png|Rule 138
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| Image:WolframRule139.png|Rule 139
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| Image:WolframRule140.png|Rule 140
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| Image:WolframRule141.png|Rule 141
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| Image:WolframRule142.png|Rule 142
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| Image:WolframRule143.png|Rule 143
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| Image:WolframRule144.png|Rule 144
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| Image:WolframRule145.png|Rule 145
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| Image:WolframRule146.png|Rule 146
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| Image:WolframRule147.png|Rule 147
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| Image:WolframRule148.png|Rule 148
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| Image:WolframRule149.png|Rule 149
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| Image:WolframRule150.png|Rule 150
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| Image:WolframRule151.png|Rule 151
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| Image:WolframRule152.png|Rule 152
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| Image:WolframRule153.png|Rule 153
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| Image:WolframRule154.png|Rule 154
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| Image:WolframRule155.png|Rule 155
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| Image:WolframRule156.png|Rule 156
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| Image:WolframRule157.png|Rule 157
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| Image:WolframRule158.png|Rule 158
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| Image:WolframRule159.png|Rule 159
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| Image:WolframRule160.png|Rule 160
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| Image:WolframRule161.png|Rule 161
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| Image:WolframRule162.png|Rule 162
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| Image:WolframRule163.png|Rule 163
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| Image:WolframRule164.png|Rule 164
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| Image:WolframRule165.png|Rule 165
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| Image:WolframRule166.png|Rule 166
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| Image:WolframRule167.png|Rule 167
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| Image:WolframRule168.png|Rule 168
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| Image:WolframRule169.png|Rule 169
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| Image:WolframRule170.png|Rule 170
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| Image:WolframRule171.png|Rule 171
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| Image:WolframRule172.png|Rule 172
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| Image:WolframRule173.png|Rule 173
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| Image:WolframRule174.png|Rule 174
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| Image:WolframRule175.png|Rule 175
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| Image:WolframRule176.png|Rule 176
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| Image:WolframRule177.png|Rule 177
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| Image:WolframRule178.png|Rule 178
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| Image:WolframRule179.png|Rule 179
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| Image:WolframRule180.png|Rule 180
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| Image:WolframRule181.png|Rule 181
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| Image:WolframRule182.png|Rule 182
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| Image:WolframRule183.png|Rule 183
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| Image:WolframRule184.png|Rule 184
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| Image:WolframRule185.png|Rule 185
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| Image:WolframRule186.png|Rule 186
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| Image:WolframRule187.png|Rule 187
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| Image:WolframRule188.png|Rule 188
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| Image:WolframRule189.png|Rule 189
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| Image:WolframRule190.png|Rule 190
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| Image:WolframRule191.png|Rule 191
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| Image:WolframRule192.png|Rule 192
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| Image:WolframRule193.png|Rule 193
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| Image:WolframRule194.png|Rule 194
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| Image:WolframRule195.png|Rule 195
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| Image:WolframRule196.png|Rule 196
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| Image:WolframRule197.png|Rule 197
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| Image:WolframRule198.png|Rule 198
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| Image:WolframRule199.png|Rule 199
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| </gallery>
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| | |
| <gallery widths="100px" heights="100px">
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| Image:WolframRule200.png|Rule 200
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| Image:WolframRule201.png|Rule 201
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| Image:WolframRule202.png|Rule 202
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| Image:WolframRule203.png|Rule 203
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| Image:WolframRule204.png|Rule 204
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| Image:WolframRule205.png|Rule 205
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| Image:WolframRule206.png|Rule 206
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| Image:WolframRule207.png|Rule 207
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| Image:WolframRule208.png|Rule 208
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| Image:WolframRule209.png|Rule 209
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| Image:WolframRule210.png|Rule 210
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| Image:WolframRule211.png|Rule 211
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| Image:WolframRule212.png|Rule 212
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| Image:WolframRule213.png|Rule 213
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| Image:WolframRule214.png|Rule 214
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| Image:WolframRule215.png|Rule 215
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| Image:WolframRule216.png|Rule 216
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| Image:WolframRule217.png|Rule 217
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| Image:WolframRule218.png|Rule 218
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| Image:WolframRule219.png|Rule 219
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| Image:WolframRule220.png|Rule 220
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| Image:WolframRule221.png|Rule 221
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| Image:WolframRule222.png|Rule 222
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| Image:WolframRule223.png|Rule 223
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| Image:WolframRule224.png|Rule 224
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| Image:WolframRule225.png|Rule 225
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| Image:WolframRule226.png|Rule 226
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| Image:WolframRule227.png|Rule 227
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| Image:WolframRule228.png|Rule 228
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| Image:WolframRule229.png|Rule 229
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| Image:WolframRule230.png|Rule 230
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| Image:WolframRule231.png|Rule 231
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| Image:WolframRule232.png|Rule 232
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| Image:WolframRule233.png|Rule 233
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| Image:WolframRule234.png|Rule 234
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| Image:WolframRule235.png|Rule 235
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| Image:WolframRule236.png|Rule 236
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| Image:WolframRule237.png|Rule 237
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| Image:WolframRule238.png|Rule 238
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| Image:WolframRule239.png|Rule 239
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| Image:WolframRule240.png|Rule 240
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| Image:WolframRule241.png|Rule 241
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| Image:WolframRule242.png|Rule 242
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| Image:WolframRule243.png|Rule 243
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| Image:WolframRule244.png|Rule 244
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| Image:WolframRule245.png|Rule 245
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| Image:WolframRule246.png|Rule 246
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| Image:WolframRule247.png|Rule 247
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| Image:WolframRule248.png|Rule 248
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| Image:WolframRule249.png|Rule 249
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| Image:WolframRule250.png|Rule 250
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| Image:WolframRule251.png|Rule 251
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| Image:WolframRule252.png|Rule 252
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| Image:WolframRule253.png|Rule 253
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| Image:WolframRule254.png|Rule 254
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| Image:WolframRule255.png|Rule 255
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| </gallery>
| |
| -->
| |
| <!-- NB. Mathworld has formulas for rules 220 and 222 interchanged -->
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| | |
| ==Random initial state==
| |
| <!-- [[Rule 34]] links to this section -->
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| | |
| A second way to investigate the behavior of these automata is to examine its history starting with a random state. This behavior can be better understood in terms of Wolfram classes. Wolfram gives the following examples as typical rules of each class.<ref>Stephan Wolfram, ''A New Kind of Science'' p223 ff.</ref>
| |
| * Class 1: Cellular automata which rapidly converge to a uniform state. Examples are rules 0, 32, 160 and 232.
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| * Class 2: Cellular automata which rapidly converge to a repetitive or stable state. Examples are rules 4, 108, 218 and 250.
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| * Class 3: Cellular automata which appear to remain in a random state. Examples are rules 22, 30, 126, 150, 182.
| |
| * Class 4: Cellular automata which form areas of repetitive or stable states, but also form structures that interact with each other in complicated ways. An example is [[rule 110]]. Rule 110 has been shown to be capable of universal computation.<ref>[http://www30.wolframalpha.com/input/?i=rule+110 Rule 110 - Wolfram|Alpha]</ref>
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| | |
| Each computed result is placed under that results' source creating a two-dimensional representation of the system's evolution. The 88 inequivalent rules are as follows, evolved from random initial conditions:
| |
| <gallery widths="100px" heights="101px">
| |
| Image:Rule0rand.png|Rule 0
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| Image:Rule1rand.png|Rule 1
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| Image:Rule2rand.png|Rule 2
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| Image:Rule3rand.png|Rule 3
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| Image:Rule4rand.png|Rule 4
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| Image:Rule5rand.png|Rule 5
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| Image:Rule6rand.png|Rule 6
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| Image:Rule7rand.png|Rule 7
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| Image:Rule8rand.png|Rule 8
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| Image:Rule9rand.png|Rule 9
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| Image:Rule10rand.png|Rule 10
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| Image:Rule11rand.png|Rule 11
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| Image:Rule12rand.png|Rule 12
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| Image:Rule13rand.png|Rule 13
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| Image:Rule14rand.png|Rule 14
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| Image:Rule15rand.png|Rule 15
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| Image:Rule18rand.png|Rule 18
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| Image:Rule19rand.png|Rule 19
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| Image:Rule22rand.png|Rule 22
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| Image:Rule23rand.png|Rule 23
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| Image:Rule24rand.png|Rule 24
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| Image:Rule25rand.png|Rule 25
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| Image:Rule26rand.png|Rule 26
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| Image:Rule27rand.png|Rule 27
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| Image:Rule28rand.png|Rule 28
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| Image:Rule29rand.png|Rule 29
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| Image:Rule30rand.png|[[Rule 30]]
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| Image:Rule32rand.png|Rule 32
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| Image:Rule33rand.png|Rule 33
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| Image:Rule34rand.png|Rule 34
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| Image:Rule35rand.png|Rule 35
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| Image:Rule36rand.png|Rule 36
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| Image:Rule37rand.png|Rule 37
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| Image:Rule38rand.png|Rule 38
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| Image:Rule40rand.png|Rule 40
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| Image:Rule41rand.png|Rule 41
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| Image:Rule42rand.png|Rule 42
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| Image:Rule43rand.png|Rule 43
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| Image:Rule44rand.png|Rule 44
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| Image:Rule45rand.png|Rule 45
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| Image:Rule46rand.png|Rule 46
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| Image:Rule50rand.png|Rule 50
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| Image:Rule51rand.png|Rule 51
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| Image:Rule54rand.png|Rule 54
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| Image:Rule56rand.png|Rule 56
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| Image:Rule57rand.png|Rule 57
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| Image:Rule58rand.png|Rule 58
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| Image:Rule60rand.png|Rule 60
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| Image:Rule62rand.png|Rule 62
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| Image:Rule72rand.png|Rule 72
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| Image:Rule73rand.png|Rule 73
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| Image:Rule74rand.png|Rule 74
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| Image:Rule76rand.png|Rule 76
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| Image:Rule77rand.png|Rule 77
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| Image:Rule78rand.png|Rule 78
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| Image:Rule90rand.png|[[Rule 90]]
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| Image:Rule94rand.png|Rule 94
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| Image:Rule104rand.png|Rule 104
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| Image:Rule105rand.png|Rule 105
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| Image:Rule106rand.png|Rule 106
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| Image:Rule108rand.png|Rule 108
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| Image:Rule110rand.png|[[Rule 110]]
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| Image:Rule122rand.png|Rule 122
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| Image:Rule126rand.png|Rule 126
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| Image:Rule128rand.png|Rule 128
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| Image:Rule130rand.png|Rule 130
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| Image:Rule132rand.png|Rule 132
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| Image:Rule134rand.png|Rule 134
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| Image:Rule136rand.png|Rule 136
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| Image:Rule138rand.png|Rule 138
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| Image:Rule140rand.png|Rule 140
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| Image:Rule142rand.png|Rule 142
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| Image:Rule146rand.png|Rule 146
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| Image:Rule150rand.png|Rule 150
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| Image:Rule152rand.png|Rule 152
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| Image:Rule154rand.png|Rule 154
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| Image:Rule156rand.png|Rule 156
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| Image:Rule160rand.png|Rule 160
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| Image:Rule162rand.png|Rule 162
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| Image:Rule164rand.png|Rule 164
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| Image:Rule168rand.png|Rule 168
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| Image:Rule170rand.png|Rule 170
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| Image:Rule172rand.png|Rule 172
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| Image:Rule178rand.png|Rule 178
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| Image:Rule184rand.png|[[Rule 184]]
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| Image:Rule200rand.png|Rule 200
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| Image:Rule204rand.png|Rule 204
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| Image:Rule232rand.png|Rule 232
| |
| </gallery>
| |
| | |
| ===Unusual cases===
| |
| In some cases the behavior of a cellular automaton is not immediately obvious. For example, for Rule 62, interacting structures develop as in a Class 4. But in these interactions at least one of the structures is annihilated so the automaton eventually enters a repetitive state and the cellular automaton is Class 2.<ref>[http://www30.wolframalpha.com/input/?i=rule+62 Rule 62 - Wolfram|Alpha]</ref>
| |
| | |
| Rule 73 is Class 2<ref>[http://www30.wolframalpha.com/input/?i=rule+73 Rule 73 - Wolfram|Alpha]</ref> because any time there are two consecutive 1s surrounded by 0s, this feature is preserved in succeeding generations. This effectively creates walls which block the flow of information between different parts of the array. There are a finite number of possible configurations in the section between two walls so the automaton must eventually start repeating inside each section, though the period may be very long if the section is wide enough. These walls will form with probability 1 for completely random initial conditions. However, if the condition is added that the lengths of runs of consecutive 0s or 1s must always be odd, then the automaton displays Class 3 behavior since the walls can never form.
| |
| | |
| Rule 54 is Class 4,<ref>[http://www30.wolframalpha.com/input/?i=rule+54 Rule 54 - Wolfram|Alpha]</ref> but it remains unknown whether it is capable of universal computation. Interacting structures form, but structures that are useful for computation have yet to be found.<ref>''A New Kind of Science'' p697</ref>
| |
| | |
| ==Summed or averaged histories==
| |
| A third way to investigate the behavior of these automata is to examine the summed or averaged histories starting from a given state over all 256 rules.<ref>[[Alex Wissner-Gross|A. D. Wissner-Gross]], "[http://www.alexwg.org/link?url=http%3A%2F%2Fwww.alexwg.org%2Fpublications%2FJCellAuto_4-27.pdf Pattern formation without favored local interactions]", ''Journal of Cellular Automata'' 4, 27-36 (2008).</ref> Surprisingly, despite the fact that no local interaction is favored by such a sum or average, rich patterns still emerge.
| |
| | |
| ==References==
| |
| *{{MathWorld|title=Elementary Cellular Automaton|urlname=ElementaryCellularAutomaton}}
| |
| *{{MathWorld|title=Rule 30|urlname=Rule30}}
| |
| *{{MathWorld|title=Rule 50|urlname=Rule50}}
| |
| *{{MathWorld|title=Rule 54|urlname=Rule54}}
| |
| *{{MathWorld|title=Rule 60|urlname=Rule60}}
| |
| *{{MathWorld|title=Rule 62|urlname=Rule62}}
| |
| *{{MathWorld|title=Rule 90|urlname=Rule90}}
| |
| *{{MathWorld|title=Rule 94|urlname=Rule94}}
| |
| *{{MathWorld|title=Rule 102|urlname=Rule102}}
| |
| *{{MathWorld|title=Rule 110|urlname=Rule110}}
| |
| *{{MathWorld|title=Rule 126|urlname=Rule126}}
| |
| *{{MathWorld|title=Rule 150|urlname=Rule150}}
| |
| *{{MathWorld|title=Rule 158|urlname=Rule158}}
| |
| *{{MathWorld|title=Rule 182|urlname=Rule182}}
| |
| *{{MathWorld|title=Rule 188|urlname=Rule188}}
| |
| *{{MathWorld|title=Rule 190|urlname=Rule190}}
| |
| *{{MathWorld|title=Rule 220|urlname=Rule220}}
| |
| *{{MathWorld|title=Rule 222|urlname=Rule222}}
| |
| | |
| {{reflist}}
| |
| | |
| ==External links==
| |
| {{Commons category|Elementary cellular automata}}
| |
| * [http://atlas.wolfram.com/01/01 "Elementary Cellular Automata" at the ''Wolfram Atlas of Simple Programs'']
| |
| * [http://ilmoeuro.ilmainenwebhotelli.com/eca/ Elementary cellular automaton demonstration (requires JavaScript and a modern browser)]
| |
| * [http://www.pouet.net/prod.php?which=60478 32 bytes long MS-DOS executable drawing by cellular automaton] ([[Rule 110]] by default)
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| | |
| [[Category:Cellular automata]]
| |