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The simplest nontrivial CA would be one-dimensional, with two possible states per cell, and a cell's neighbors defined to be the adjacent cells on either side of it. A cell and its two neighbors form a neighborhood of 3 cells, so there are 23=8 possible patterns for a neighborhood. There are then 28=256 possible rules. These 256 CAs are generally referred to using a standard naming convention invented by Wolfram. The name of a CA is the decimal number which, in binary, gives the rule table, with the eight possible neigh ...

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Cellular automaton, Cellular automaton - History of cellular automata, Cellular automaton - The simplest cellular automata, Cellular automaton - Reversible cellular automata, Cellular automaton - Totalistic cellular automata, Cellular automaton - Uses in cryptography, Cellular automaton - Related automata, Cellular automaton - Cellular automata in nature, Cellular automaton - Cellular automata in the chemistry lab, Cellular automaton - Articles on specific cellular automata

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Let X and Y be sets. Let f and g be functions, both from X to Y. Then the equaliser of f and g is the set of elements x of X such that f(x) equals g(x) in Y. Symbolically: The equaliser may be denoted Eq(f,g) or a variation on that theme (such as with lowercase letters "eq"). In informal contexts, the ...

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Equaliser, Equaliser - Definitions, Equaliser - Difference kernels, Equaliser - In category theory

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There are many possible generalizations of the CA concept. One way is by using something other than a rectangular (cubic, etc.) grid. For example, if a plane is tiled with equilateral triangles, those triangles could be used as cells. Also, rules can be probabilistic rather than deterministic. A probabilistic rule gives, for each pattern at time t, the probabilities that the central cell will transition to each possible state at time t+1. Sometimes a simpler rule is used; for example: "The rule is the Game of Life, but on each time step there is a 0.001% probability ...

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Cellular automaton, Cellular automaton - History of cellular automata, Cellular automaton - The simplest cellular automata, Cellular automaton - Reversible cellular automata, Cellular automaton - Totalistic cellular automata, Cellular automaton - Uses in cryptography, Cellular automaton - Related automata, Cellular automaton - Cellular automata in nature, Cellular automaton - Cellular automata in the chemistry lab, Cellular automaton - Articles on specific cellular automata

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Patterns of certain seashells, like the ones in Conus and Cymbiola genus, are generated by natural cellular automata. The pigment cells reside in a narrow band along the shell's lip. Each cell secretes pigments according to the activating and inhibiting activity of its neighbours, obeying a natural version of a mathematical rule. The cell band leaves the colored pattern on the shell as it slowly grows. For instance, the widespread species Conus text ...

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Cellular automaton, Cellular automaton - History of cellular automata, Cellular automaton - The simplest cellular automata, Cellular automaton - Reversible cellular automata, Cellular automaton - Totalistic cellular automata, Cellular automaton - Uses in cryptography, Cellular automaton - Related automata, Cellular automaton - Cellular automata in nature, Cellular automaton - Cellular automata in the chemistry lab, Cellular automaton - Articles on specific cellular automata

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The notion of function is generalizes to the notion of morphism in the context of category theory. A category is a collection of objects and morphisms, each morphism is an ordered triple (X, Y, f), where f is a rule connecting domain X and codomain Y, and X and Y are objects in the collection. Ordinary functions are sometimes referred to as morphisms in a concrete category. ...

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Function mathematics, Function mathematics - Mathematical definition of a function, Function mathematics - First definition, Function mathematics - Second definition, Function mathematics - History of the concept, Function mathematics - Functions in other fields, Function mathematics - Domain codomain argument image, Function mathematics - Graph of a function, Function mathematics - Specifying a function, Function mathematics - Functions with multiple inputs and outputs, Function mathematics - Functions of two or more variables, Function mathematics - Functions with output in a product set, Function mathematics - Binary operations, Function mathematics - Argument order and lambda notation, Function mathematics - Examples of functions, Function mathematics - Image of a set, Function mathematics - Range of a function, Function mathematics - Preimage of a set, Function mathematics - Composing functions, Function mathematics - Inverse function, Function mathematics - Set of all functions, Function mathematics - Is a function more than its graph?, Function mathematics - Partial functions and multi-functions, Function mathematics - Classes of functions, Function mathematics - Injective surjective bijective, Function mathematics - Other properties, Function mathematics - Restrictions and extensions, Function mathematics - Pointwise operations, Function mathematics - Computable and non-computable functions, Function mathematics - Lambda calculus, Function mathematics - Functions in category theory

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It should be noted that a decision problem is always a set of related problems which is in some sense large enough. A single problem P is always trivially decidable by assigning the constant function f(P)≡0 or f(P)≡1 to it. Nearly every problem can be cast as a decision problem by using reductions, often with little effect on the amount of time or space needed to solve the problem. Many traditional hard problems have been cast as decision problems because this makes them easier to study and to solve, and proving that these problems are hard suffices to show th ...

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Decision problem, Decision problem - Definition, Decision problem - Notes, Decision problem - Examples, Decision problem - History

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Rule 30 was originally suggested as a possible stream cipher for use in cryptography. Cellular automata have been proposed for public key cryptography. The one way function is the evolution of a finite CA whose inverse is hard to find. Given the rule, anyone can easily calculate future states, but it is very difficult to calculate previous states. However, the designer of the rule can create it in such a way as to be able to easily invert it. Therefore, it is a trapdoor function, and can be used as a public-key cryptos ...

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Cellular automaton, Cellular automaton - History of cellular automata, Cellular automaton - The simplest cellular automata, Cellular automaton - Reversible cellular automata, Cellular automaton - Totalistic cellular automata, Cellular automaton - Uses in cryptography, Cellular automaton - Related automata, Cellular automaton - Cellular automata in nature, Cellular automaton - Cellular automata in the chemistry lab, Cellular automaton - Articles on specific cellular automata

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If f: X → R and g: X → R are functions with common domain X and codomain is a ring R, then one can define the sum function f + g: X → R and the product function f × g: X → R as follows: (f + g)(x) = f(x) + g(x) (f × g)(x) = f(x) × < ...

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Function mathematics, Function mathematics - Mathematical definition of a function, Function mathematics - First definition, Function mathematics - Second definition, Function mathematics - History of the concept, Function mathematics - Functions in other fields, Function mathematics - Domain codomain argument image, Function mathematics - Graph of a function, Function mathematics - Specifying a function, Function mathematics - Functions with multiple inputs and outputs, Function mathematics - Functions of two or more variables, Function mathematics - Functions with output in a product set, Function mathematics - Binary operations, Function mathematics - Argument order and lambda notation, Function mathematics - Examples of functions, Function mathematics - Image of a set, Function mathematics - Range of a function, Function mathematics - Preimage of a set, Function mathematics - Composing functions, Function mathematics - Inverse function, Function mathematics - Set of all functions, Function mathematics - Is a function more than its graph?, Function mathematics - Partial functions and multi-functions, Function mathematics - Classes of functions, Function mathematics - Injective surjective bijective, Function mathematics - Other properties, Function mathematics - Restrictions and extensions, Function mathematics - Pointwise operations, Function mathematics - Computable and non-computable functions, Function mathematics - Lambda calculus, Function mathematics - Functions in category theory

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The disjoint union space X, together with the canonical injections, can be characterized by the following universal property: If Y is a topological space, and fi : Xi → Y is a continuous map for each i ∈ I, then there exists precisely one continuous map f : X → Y such that the following set of diagrams commute: This shows that the disjoint union is the coproduct in the category of topological spaces. It follows from the a ...

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Disjoint union topology, Disjoint union topology - Definition, Disjoint union topology - Properties, Disjoint union topology - Examples, Disjoint union topology - Preservation of topological properties

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Function mathematics - Functions of two or more variables. The concept of function can be extended to an object that takes a combination of two (or more) argument values to a single result. This intuitive concept is formalized by a function whose domain is the Cartesian product of two or more sets. For example, consider the multiplication function that associates two integers to their product: f(x, y) = x·y. This function can be defined formally as having domain Z ...

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Function mathematics, Function mathematics - Mathematical definition of a function, Function mathematics - First definition, Function mathematics - Second definition, Function mathematics - History of the concept, Function mathematics - Functions in other fields, Function mathematics - The vocabulary of functions, Function mathematics - Specifying a function, Function mathematics - Functions with multiple inputs and outputs, Function mathematics - Functions of two or more variables, Function mathematics - Functions with output in a product set, Function mathematics - Binary operations, Function mathematics - Set of all functions, Function mathematics - Is a function more than its graph?, Function mathematics - Partial functions and multi-functions, Function mathematics - Other properties, Function mathematics - Restrictions and extensions, Function mathematics - Pointwise operations, Function mathematics - Computable and non-computable functions, Function mathematics - Lambda calculus, Function mathematics - Functions in category theory

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Informally, a restriction of a function f is the result of trimming its graph to a smaller domain. More precisely, if f is a function from a X to Y, and S is any subset of X, the restriction of f to S is the function f|S from S to Y such that f|S(s) = f(s) for all s in S. The restriction f|S can also be expressed as the composition f incS,X, where incSSee also:

Function mathematics, Function mathematics - Mathematical definition of a function, Function mathematics - First definition, Function mathematics - Second definition, Function mathematics - History of the concept, Function mathematics - Functions in other fields, Function mathematics - Domain codomain argument image, Function mathematics - Graph of a function, Function mathematics - Specifying a function, Function mathematics - Functions with multiple inputs and outputs, Function mathematics - Functions of two or more variables, Function mathematics - Functions with output in a product set, Function mathematics - Binary operations, Function mathematics - Argument order and lambda notation, Function mathematics - Examples of functions, Function mathematics - Image of a set, Function mathematics - Range of a function, Function mathematics - Preimage of a set, Function mathematics - Composing functions, Function mathematics - Inverse function, Function mathematics - Set of all functions, Function mathematics - Is a function more than its graph?, Function mathematics - Partial functions and multi-functions, Function mathematics - Classes of functions, Function mathematics - Injective surjective bijective, Function mathematics - Other properties, Function mathematics - Restrictions and extensions, Function mathematics - Pointwise operations, Function mathematics - Computable and non-computable functions, Function mathematics - Lambda calculus, Function mathematics - Functions in category theory

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Most mathematicians define a binary relation (and hence a function) as an ordered triple (X, Y, G), where X and Y are the domain and codomain sets, and G is the graph of f. However, some mathematicians define a relation as being simply the set of pairs G, without explicitly giving the domain and co-domain. There are advantages and disadvantages to each definition, but either of them is satisfactory for most uses of functions in mathematics. The explicit domain and ...

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Function mathematics, Function mathematics - Mathematical definition of a function, Function mathematics - First definition, Function mathematics - Second definition, Function mathematics - History of the concept, Function mathematics - Functions in other fields, Function mathematics - The vocabulary of functions, Function mathematics - Specifying a function, Function mathematics - Functions with multiple inputs and outputs, Function mathematics - Functions of two or more variables, Function mathematics - Functions with output in a product set, Function mathematics - Binary operations, Function mathematics - Set of all functions, Function mathematics - Is a function more than its graph?, Function mathematics - Partial functions and multi-functions, Function mathematics - Other properties, Function mathematics - Restrictions and extensions, Function mathematics - Pointwise operations, Function mathematics - Computable and non-computable functions, Function mathematics - Lambda calculus, Function mathematics - Functions in category theory

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Proper map - Definition. A function f : X → Y between two topological spaces is proper if and only if the preimage of every compact set in Y is compact in X. An equivalent, possibly more intuitive definition is as follows: We say an infinite sequence of points {pi} in a topological space X escapes to infinity if, for every compact set S ⊂ X, only finitely many points pi are in See also:

Proper map, Proper map - Topological spaces, Proper map - Definition, Proper map - Properties, Proper map - Examples, Proper map - Algebraic varieties and schemes, Proper map - Definition, Proper map - Examples, Proper map - Valuative criterion of properness, Proper map - Stein factorization

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It is possible to define a cohomology theory for sheaves of abelian groups (sheaf cohomology) that can give much useful, more concrete information. The main issue is the existence of the long exact sequence coming from an exact sequence of sheaves. In applications emphasis was placed on sheaves on spaces that were less well-behaved than finite complexes. For example, in algebraic geometry spaces carry ...

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Sheaf mathematics, Sheaf mathematics - Introduction, Sheaf mathematics - The formal definition, Sheaf mathematics - Definition of a presheaf, Sheaf mathematics - The gluing axiom, Sheaf mathematics - Examples, Sheaf mathematics - Morphisms of sheaves, Sheaf mathematics - Stalks of a sheaf at a point and germs of functions, Sheaf mathematics - The étale space of a sheaf, Sheaf mathematics - Generalizations, Sheaf mathematics - History

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The first origins of sheaf theory are hard to pin down — they may be co-extensive with the idea of analytic continuation. It took about 15 years for a recognisable, free-standing theory of sheaves to emerge from the foundational work on cohomology. 1936 Eduard Čech introduces the nerve construction, for associating a simplicial complex to an open covering. 1938 Hassler Whitney gives a 'modern' definition of cohomology, summarizing the work since J. W. Alexander and Kolmogorov first defined cochainsSee also:

Sheaf mathematics, Sheaf mathematics - Introduction, Sheaf mathematics - The formal definition, Sheaf mathematics - Definition of a presheaf, Sheaf mathematics - The gluing axiom, Sheaf mathematics - Examples, Sheaf mathematics - Morphisms of sheaves, Sheaf mathematics - Stalks of a sheaf at a point and germs of functions, Sheaf mathematics - The étale space of a sheaf, Sheaf mathematics - Generalizations, Sheaf mathematics - History

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Abelian group. A group (G,*) is abelian if * is commutative, i.e. g*h=h*g for all g,h ∈ G. Likewise, a group is nonabelian if this relation fails to hold for any pair g,h ∈ G. Finitely generated group. If there exists a finite set S such that <S> = G, then G is said to be finitely generated. If S can be taken to have just one element, G is a cyclic group of finite order, an infinite ...

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Glossary of group theory, Glossary of group theory - Basic definitions, Glossary of group theory - Types of groups

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In early developments of sheaf theory, it was shown that giving a sheaf F on X is as good as giving a certain topological space E together with a continuous map from E to X. More precisely: to every sheaf F of sets on X there exists a local homeomorphism π: E → X such that F is isomorphic to the sheaf o ...

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Sheaf mathematics, Sheaf mathematics - Introduction, Sheaf mathematics - The formal definition, Sheaf mathematics - Definition of a presheaf, Sheaf mathematics - The gluing axiom, Sheaf mathematics - Examples, Sheaf mathematics - Morphisms of sheaves, Sheaf mathematics - Stalks of a sheaf at a point and germs of functions, Sheaf mathematics - The étale space of a sheaf, Sheaf mathematics - Generalizations, Sheaf mathematics - History

Read more here: » Sheaf mathematics: Encyclopedia II - Sheaf mathematics - The étale space of a sheaf

Fix a point x of X. We would like to study the behavior of F near the point x. In analytical terms, we would like to somehow take the limit as we get nearer and nearer to the point x. The corresponding concept is to take the direct limit of F(N) as N runs over the open neighbourhoods of x ordered by inclusion (in categorical terminology, this is an example of a colimit). We denote this limit by Fx and call it the stalk of F at x. If F ...

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Sheaf mathematics, Sheaf mathematics - Introduction, Sheaf mathematics - The formal definition, Sheaf mathematics - Definition of a presheaf, Sheaf mathematics - The gluing axiom, Sheaf mathematics - Examples, Sheaf mathematics - Morphisms of sheaves, Sheaf mathematics - Stalks of a sheaf at a point and germs of functions, Sheaf mathematics - The étale space of a sheaf, Sheaf mathematics - Generalizations, Sheaf mathematics - History

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In addition to the sheaves of continuous functions, differentiable functions and vector fields given in the introduction, sheaves of sections are very important examples. Suppose E and X are topological spaces and π : E → X is a continuous map. For every open set U in X, let F(U) be the set all continuous maps f : U → E such that π(f(x)) = x for all x in U. Such a function f is called a section of π. ...

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Sheaf mathematics, Sheaf mathematics - Introduction, Sheaf mathematics - The formal definition, Sheaf mathematics - Definition of a presheaf, Sheaf mathematics - The gluing axiom, Sheaf mathematics - Examples, Sheaf mathematics - Morphisms of sheaves, Sheaf mathematics - Stalks of a sheaf at a point and germs of functions, Sheaf mathematics - The étale space of a sheaf, Sheaf mathematics - Generalizations, Sheaf mathematics - History

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Since the Church-Turing thesis states that computable functions are defined equivalently by Turing machines and other models of computation, we can state the definition as A countable set S is called recursively enumerable if there exists a Turing machine that always halts when given an element of S as input, and that never halts when given an input that does not belong to S. This is also a ...

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Recursively enumerable set, Recursively enumerable set - Definition, Recursively enumerable set - Remarks, Recursively enumerable set - Examples, Recursively enumerable set - Properties

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Let F and G be two sheaves on X both with values in the category C. We define a morphism from G to F to be a family of morphisms φU : G(U) → F(U) in the category C for all opens U in X which commute with the restriction maps. That is, the following diagram must commute for each pair of open sets U ⊆ V in X. If F and G are considered as contravariant functors from TopXSee also:

Sheaf mathematics, Sheaf mathematics - Introduction, Sheaf mathematics - The formal definition, Sheaf mathematics - Definition of a presheaf, Sheaf mathematics - The gluing axiom, Sheaf mathematics - Examples, Sheaf mathematics - Morphisms of sheaves, Sheaf mathematics - Stalks of a sheaf at a point and germs of functions, Sheaf mathematics - The étale space of a sheaf, Sheaf mathematics - Generalizations, Sheaf mathematics - History

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Vector bundle, a fiber bundle whose fibers are vector spaces and whose transition functions are linear maps. Vector field, a section of a vector bundle. More specifically, a vector field can mean a section of the tangent bundle. ...

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Glossary of differential geometry and topology, Glossary of differential geometry and topology - A, Glossary of differential geometry and topology - B, Glossary of differential geometry and topology - C, Glossary of differential geometry and topology - D, Glossary of differential geometry and topology - E, Glossary of differential geometry and topology - F, Glossary of differential geometry and topology - G, Glossary of differential geometry and topology - H, Glossary of differential geometry and topology - I, Glossary of differential geometry and topology - L, Glossary of differential geometry and topology - M, Glossary of differential geometry and topology - P, Glossary of differential geometry and topology - S, Glossary of differential geometry and topology - T, Glossary of differential geometry and topology - V, Glossary of differential geometry and topology - W

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