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Computability In The Limit
In computability theory, a function is called limit computable if it is the limit of a uniformly computable sequence of functions. The terms computable in the limit, limit recursive and recursively approximable are also used. One can think of limit computable functions as those admitting an eventually correct computable guessing procedure at their true value. A set is limit computable just when its characteristic function is limit computable. If the sequence is uniformly computable relative to ''D'', then the function is limit computable in ''D''. Formal definition A total function r(x) is limit computable if there is a total computable function \hat(x,s) such that : \displaystyle r(x) = \lim_ \hat(x,s) The total function r(x) is limit computable in ''D'' if there is a total function \hat(x,s) computable in ''D'' also satisfying : \displaystyle r(x) = \lim_ \hat(x,s) A set of natural numbers is defined to be computable in the limit if and only if its characteristic functio ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Computability Theory
Computability theory, also known as recursion theory, is a branch of mathematical logic, computer science, and the theory of computation that originated in the 1930s with the study of computable functions and Turing degrees. The field has since expanded to include the study of generalized computability and definable set, definability. In these areas, computability theory overlaps with proof theory and effective descriptive set theory. Basic questions addressed by computability theory include: * What does it mean for a function (mathematics), function on the natural numbers to be computable? * How can noncomputable functions be classified into a hierarchy based on their level of noncomputability? Although there is considerable overlap in terms of knowledge and methods, mathematical computability theorists study the theory of relative computability, reducibility notions, and degree structures; those in the computer science field focus on the theory of computational complexity theory ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Computable Numbers
In mathematics, computable numbers are the real numbers that can be computed to within any desired precision by a finite, terminating algorithm. They are also known as the recursive numbers, effective numbers, computable reals, or recursive reals. The concept of a computable real number was introduced by Émile Borel in 1912, using the intuitive notion of computability available at the time. Equivalent definitions can be given using μ-recursive functions, Turing machines, or λ-calculus as the formal representation of algorithms. The computable numbers form a real closed field and can be used in the place of real numbers for many, but not all, mathematical purposes. Informal definition In the following, Marvin Minsky defines the numbers to be computed in a manner similar to those defined by Alan Turing in 1936; i.e., as "sequences of digits interpreted as decimal fractions" between 0 and 1: The key notions in the definition are (1) that some ''n'' is specified at the start, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Robert I
Robert I may refer to: * Robert I, Duke of Neustria (697–748) *Robert I of France (866–923), King of France, 922–923, rebelled against Charles the Simple * Rollo, Duke of Normandy (c. 846 – c. 930; reigned 911–927) * Robert I Archbishop of Rouen (d. 1037), Archbishop of Rouen, 989–1037, son of Duke Richard I of Normandy * Robert the Magnificent (1000–1035), also named Robert I, Duke of Normandy, 1027–1035), father of William the Conqueror. Sometimes known as Robert II, with Rollo of Normandy, c. 860 – c. 932, as Robert I because Robert was his baptismal name when he became a Christian * Robert I, Duke of Burgundy (1011–1076), Duke of Burgundy, 1032–1076 * Robert I, Count of Flanders (1029–1093), also named Robert the Frisian, Count of Flanders, 1071–1093 * Robert I de Brus (ca. 1078 – 1141/1142) * Robert I of Dreux (c. 1123 – 1188), Count of Braine in France, son of King Louis VI *Robert I of Artois (1216–1250), son of King Louis VIII of France *Ro ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Jürgen Schmidhuber
Jürgen Schmidhuber (born 17 January 1963) is a German computer scientist noted for his work in the field of artificial intelligence, specifically artificial neural networks. He is a scientific director of the Dalle Molle Institute for Artificial Intelligence Research in Switzerland. He is also director of the Artificial Intelligence Initiative and professor of the Computer Science program in the Computer, Electrical, and Mathematical Sciences and Engineering (CEMSE) division at the King Abdullah University of Science and Technology (KAUST) in Saudi Arabia. He is best known for his foundational and highly-cited work on long short-term memory (LSTM), a type of neural network architecture which was the dominant technique for various natural language processing tasks in research and commercial applications in the 2010s. He also introduced principles of dynamic neural networks, meta-learning, generative adversarial networks and linear transformers, all of which are widespread ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Specker Sequence
In computability theory, a Specker sequence is a computable, monotonically increasing, bounded sequence of rational numbers whose supremum is not a computable real number. The first example of such a sequence was constructed by Ernst Specker (1949). The existence of Specker sequences has consequences for computable analysis. The fact that such sequences exist means that the collection of all computable real numbers does not satisfy the least upper bound principle of real analysis, even when considering only computable sequences. A common way to resolve this difficulty is to consider only sequences that are accompanied by a modulus of convergence; no Specker sequence has a computable modulus of convergence. More generally, a Specker sequence is called a ''recursive counterexample'' to the least upper bound principle, i.e. a construction that shows that this theorem is false when restricted to computable reals. The least upper bound principle has also been analyzed in the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Admissible Ordinal
In set theory, an ordinal number ''α'' is an admissible ordinal if L''α'' is an admissible set (that is, a transitive model of Kripke–Platek set theory); in other words, ''α'' is admissible when ''α'' is a limit ordinal and L''α'' ⊧ Σ0-collection.. See in particulap. 265. The term was coined by Richard Platek in 1966. The first two admissible ordinals are ω and \omega_1^ (the least nonrecursive ordinal, also called the Church–Kleene ordinal). Any regular uncountable cardinal is an admissible ordinal. By a theorem of Sacks, the countable admissible ordinals are exactly those constructed in a manner similar to the Church–Kleene ordinal, but for Turing machines with oracles. One sometimes writes \omega_\alpha^ for the \alpha-th ordinal that is either admissible or a limit of admissibles; an ordinal that is both is called ''recursively inaccessible''. There exists a theory of large ordinals in this manner that is highly parallel to that of (small) large ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Alpha Recursion Theory
In recursion theory, α recursion theory is a generalisation of recursion theory to subsets of admissible ordinals \alpha. An admissible set is closed under \Sigma_1(L_\alpha) functions, where L_\xi denotes a rank of Godel's constructible hierarchy. \alpha is an admissible ordinal if L_ is a model of Kripke–Platek set theory. In what follows \alpha is considered to be fixed. Definitions The objects of study in \alpha recursion are subsets of \alpha. These sets are said to have some properties: *A set A\subseteq\alpha is said to be \alpha-recursively-enumerable if it is \Sigma_1 definable over L_\alpha, possibly with parameters from L_\alpha in the definition. *A is \alpha-recursive if both A and \alpha \setminus A (its relative complement in \alpha) are \alpha-recursively-enumerable. It's of note that \alpha-recursive sets are members of L_ by definition of L. *Members of L_\alpha are called \alpha-finite and play a similar role to the finite numbers in classical recursion th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Chaitin's Constant
In the computer science subfield of algorithmic information theory, a Chaitin constant (Chaitin omega number) or halting probability is a real number that, informally speaking, represents the probability that a randomly constructed program will halt. These numbers are formed from a construction due to Gregory Chaitin. Although there are infinitely many halting probabilities, one for each (universal, see below) method of encoding programs, it is common to use the letter to refer to them as if there were only one. Because depends on the program encoding used, it is sometimes called Chaitin's construction when not referring to any specific encoding. Each halting probability is a normal and transcendental real number that is not computable, which means that there is no algorithm to compute its digits. Each halting probability is Martin-Löf random, meaning there is not even any algorithm which can reliably guess its digits. Background The definition of a halting probability ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
First-order Arithmetic
In first-order logic, a first-order theory is given by a set of axioms in some language. This entry lists some of the more common examples used in model theory and some of their properties. Preliminaries For every natural mathematical structure there is a signature σ listing the constants, functions, and relations of the theory together with their arities, so that the object is naturally a σ-structure. Given a signature σ there is a unique first-order language ''L''σ that can be used to capture the first-order expressible facts about the σ-structure. There are two common ways to specify theories: #List or describe a set of sentences in the language ''L''σ, called the axioms of the theory. #Give a set of σ-structures, and define a theory to be the set of sentences in ''L''σ holding in all these models. For example, the "theory of finite fields" consists of all sentences in the language of fields that are true in all finite ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Halting Problem
In computability theory (computer science), computability theory, the halting problem is the problem of determining, from a description of an arbitrary computer program and an input, whether the program will finish running, or continue to run forever. The halting problem is ''Undecidable problem, undecidable'', meaning that no general algorithm exists that solves the halting problem for all possible program–input pairs. The problem comes up often in discussions of computability since it demonstrates that some functions are mathematically Definable set, definable but not Computable function, computable. A key part of the formal statement of the problem is a mathematical definition of a computer and program, usually via a Turing machine. The proof then shows, for any program that might determine whether programs halt, that a "pathological" program exists for which makes an incorrect determination. Specifically, is the program that, when called with some input, passes its own s ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Modulus Of Convergence
In real analysis, a branch of mathematics, a modulus of convergence is a function that tells how quickly a convergent sequence converges. These moduli are often employed in the study of computable analysis and constructive mathematics. If a sequence of real numbers x_i converges to a real number x, then by definition, for every real \varepsilon > 0 there is a natural number N such that if i > N then \left, x - x_i\ f(n) then \left, x - x_i\ g(n) then \left, x_i - x_j\ < 1/n. The latter definition is often employed in constructive settings, where the limit may actually be identified with the convergent sequence. Some authors use an alternate definition that replaces with . See also *Modulus of continuity
In mathematical analysis, a modu ...
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Computable
Computability is the ability to solve a problem by an effective procedure. It is a key topic of the field of computability theory within mathematical logic and the theory of computation within computer science. The computability of a problem is closely linked to the existence of an algorithm to solve the problem. The most widely studied models of computability are the Turing-computable and μ-recursive functions, and the lambda calculus, all of which have computationally equivalent power. Other forms of computability are studied as well: computability notions weaker than Turing machines are studied in automata theory, while computability notions stronger than Turing machines are studied in the field of hypercomputation. Problems A central idea in computability is that of a (computational) computational problem, problem, which is a task whose computability can be explored. There are two key types of problems: * A decision problem fixes a set ''S'', which may be a set of string ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |