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Walther Recursion
In computer programming, Walther recursion (named after Christoph Walther) is a method of analysing recursive functions that can determine if the function is definitely terminating, given finite inputs. It allows a more natural style of expressing computation than simply using primitive recursive functions. Since the halting problem cannot be solved in general, there must still be programs that terminate, but which Walther recursion cannot prove to terminate. Walther recursion may be used in total functional languages in order to allow a more liberal style of showing primitive recursion. See also * BlooP and FlooP * Termination analysis * Total Turing machine In computability theory, a decider is a Turing machine that halts for every input. A decider is also called a total Turing machineKozen, 1997 as it represents a total function. Because it always halts, such a machine is able to decide whether a gi ... References * * * Recursion {{compu-prog-stub ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Christoph Walther
Christoph Walther (born 9 August 1950) is a German computer scientist, known for his contributions to automated theorem proving. He is Professor emeritus at Darmstadt University of Technology. (Section ''Emeriti und Professoren im Ruhestand'') at Darmstadt University Web Site Selected publications On automated program termination analysis
In computer science, termination analysis is program analysis which attempts to determine whether the evaluation of a given program halts for ''each'' input. This means to determine whether the input program computes a ' ...
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Terminating
In computer science, a computation is said to diverge if it does not terminate or terminates in an exceptional state. Otherwise it is said to converge. In domains where computations are expected to be infinite, such as process calculi, a computation is said to diverge if it fails to be productive (i.e. to continue producing an action within a finite amount of time). Definitions Various subfields of computer science use varying, but mathematically precise, definitions of what it means for a computation to converge or diverge. Rewriting In abstract rewriting, an abstract rewriting system is called convergent if it is both confluent and terminating. The notation ''t'' ↓ ''n'' means that ''t'' reduces to normal form ''n'' in zero or more reductions, ''t''↓ means ''t'' reduces to some normal form in zero or more reductions, and ''t''↑ means ''t'' does not reduce to a normal form; the latter is impossible in a terminating rewriting system. In the lambda calculus an expressi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Primitive Recursive Function
In computability theory, a primitive recursive function is roughly speaking a function that can be computed by a computer program whose loops are all "for" loops (that is, an upper bound of the number of iterations of every loop can be determined before entering the loop). Primitive recursive functions form a strict subset of those general recursive functions that are also total functions. The importance of primitive recursive functions lies in the fact that most computable functions that are studied in number theory (and more generally in mathematics) are primitive recursive. For example, addition and division, the factorial and exponential function, and the function which returns the ''n''th prime are all primitive recursive. In fact, for showing that a computable function is primitive recursive, it suffices to show that its time complexity is bounded above by a primitive recursive function of the input size. It is hence not that easy to devise a computable function that is ''n ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Halting Problem
In 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. Alan Turing proved in 1936 that a general algorithm to solve the halting problem for all possible program–input pairs cannot exist. For any program that might determine whether programs halt, a "pathological" program , called with some input, can pass its own source and its input to ''f'' and then specifically do the opposite of what ''f'' predicts ''g'' will do. No ''f'' can exist that handles this case. A key part of the proof is a mathematical definition of a computer and program, which is known as a Turing machine; the halting problem is '' undecidable'' over Turing machines. It is one of the first cases of decision problems proven to be unsolvable. This proof is significant to practical computing efforts, defining a class of applications which no programming inventi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Total Functional Programming
Total functional programming (also known as strong functional programming, to be contrasted with ordinary, or ''weak'' functional programming) is a programming paradigm that restricts the range of programs to those that are provably terminating. Restrictions Termination is guaranteed by the following restrictions: # A restricted form of recursion, which operates only upon 'reduced' forms of its arguments, such as Walther recursion, substructural recursion, or "strongly normalizing" as proven by abstract interpretation of code. # Every function must be a total (as opposed to partial) function. That is, it must have a definition for everything inside its domain. #* There are several possible ways to extend commonly used partial functions such as division to be total: choosing an arbitrary result for inputs on which the function is normally undefined (such as \forall x \in \mathbb. x \div 0 = 0 for division); adding another argument to specify the result for those inputs; or exclu ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
BlooP And FlooP
and (Bounded loop and Free loop) are simple programming languages designed by Douglas Hofstadter to illustrate a point in his book ''Gödel, Escher, Bach''. BlooP is a non-Turing-complete programming language whose main control flow structure is a bounded loop (i.e. recursion is not permitted). All programs in the language must terminate, and this language can only express primitive recursive functions. FlooP is identical to BlooP except that it supports unbounded loops; it is a Turing-complete language and can express all computable functions. For example, it can express the Ackermann function, which (not being primitive recursive) cannot be written in BlooP. Borrowing from standard terminology in mathematical logic,Hofstadter (1979), p. 424. Hofstadter calls FlooP's unbounded loops MU-loops. Like all Turing-complete programming languages, FlooP suffers from the halting problem: programs might not terminate, and it is not possible, in general, to decide which programs do. BlooP ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Termination Analysis
In computer science, termination analysis is program analysis which attempts to determine whether the evaluation of a given program halts for ''each'' input. This means to determine whether the input program computes a ''total'' function. It is closely related to the halting problem, which is to determine whether a given program halts for a ''given'' input and which is undecidable. The termination analysis is even more difficult than the Halting problem: the termination analysis in the model of Turing machines as the model of programs implementing computable functions would have the goal of deciding whether a given Turing machine is a total Turing machine, and this problem is at level \Pi^0_2 of the arithmetical hierarchy and thus is strictly more difficult than the Halting problem. Now as the question whether a computable function is total is not semi-decidable, each ''sound'' termination analyzer (i.e. an affirmative answer is never given for a non-terminating program) is ''inco ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Total Turing Machine
In computability theory, a decider is a Turing machine that halts for every input. A decider is also called a total Turing machineKozen, 1997 as it represents a total function. Because it always halts, such a machine is able to decide whether a given string is a member of a formal language. The class of languages which can be decided by such machines is the set of recursive languages. Given an arbitrary Turing machine, determining whether it is a decider is an undecidable problem. This is a variant of the halting problem, which asks for whether a Turing machine halts on a specific input. Functions computable by total Turing machines In practice, many functions of interest are computable by machines that always halt. A machine that uses only finite memory on any particular input can be forced to halt for every input by restricting its flow control capabilities so that no input will ever cause the machine to enter an infinite loop. As a trivial example, a machine implementin ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Artificial Intelligence (journal)
''Artificial Intelligence'' is a scientific journal on artificial intelligence research. It was established in 1970 and is published by Elsevier. The journal is abstracted and indexed in Scopus and Science Citation Index. The 2021 Impact Factor for this journal is 14.05 and the 5-Year Impact Factor is 11.616.Journal Citation Reports ''Journal Citation Reports'' (''JCR'') is an annual publicationby Clarivate Analytics (previously the intellectual property of Thomson Reuters). It has been integrated with the Web of Science and is accessed from the Web of Science-Core Collect ... 2022, Published by Thomson Reuters References Artificial intelligence publications Computer science journals Elsevier academic journals Publications established in 1970 External links Official website {{compu-journal-stub ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Massachusetts Institute Of Technology
The Massachusetts Institute of Technology (MIT) is a private land-grant research university in Cambridge, Massachusetts. Established in 1861, MIT has played a key role in the development of modern technology and science, and is one of the most prestigious and highly ranked academic institutions in the world. Founded in response to the increasing industrialization of the United States, MIT adopted a European polytechnic university model and stressed laboratory instruction in applied science and engineering. MIT is one of three private land grant universities in the United States, the others being Cornell University and Tuskegee University. The institute has an urban campus that extends more than a mile (1.6 km) alongside the Charles River, and encompasses a number of major off-campus facilities such as the MIT Lincoln Laboratory, the Bates Center, and the Haystack Observatory, as well as affiliated laboratories such as the Broad and Whitehead Institutes. , 98 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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