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Erschienen in: Theory of Computing Systems 2/2017

19.03.2016

A Difference in Complexity Between Recursion and Tail Recursion

verfasst von: Siddharth Bhaskar

Erschienen in: Theory of Computing Systems | Ausgabe 2/2017

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Abstract

There are several ways to understand computability over first-order structures. We may admit functions given by arbitrary recursive definitions, or we may restrict ourselves to “iterative,” or tail recursive, functions computable by nothing more complicated than while loops. It is well known that in the classical case of recursion theory over the natural numbers, these two notions of computability coincide (though this is not true for all structures). We ask if there are structures over which recursion and tail recursion coincide in terms of computability, but in which a general recursive program may compute a certain function more efficiently than any tail recursion, according to some natural measure of complexity. We give a positive answer to this question, thus answering an open question in Lynch and Blum (Math. Syst. Theory. 12(1), 205-211 [5]).

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Fußnoten
1
In equality of partial functions, if one side diverges, the other must as well.
 
2
A term of co-arity k is simply a k-tuple of terms.
 
3
The other natural sequential measure of complexity for recursive programs is the sequential number of calls complexity, which measures the number of calls to the primitives during execution. This complexity measure is bounded above and (surprisingly) below by a linear function of the logical complexity (see Chapter 3 of Moschovakis [7]). This tight relationship ensures that our results will apply to both measures.
 
4
L s diverges exactly when E does.
 
5
The intuition here is that E needs to “construct” the term defining y from \(\bar {x}\) in the course of its computation, and it can increase the length of this term by at most one symbol per logical step.
 
Literatur
2.
Zurück zum Zitat Sheila, A.: Greibach. Theory of program structures: Schemes, Semantics, Verification. Springer, Verlag (1975)MATH Sheila, A.: Greibach. Theory of program structures: Schemes, Semantics, Verification. Springer, Verlag (1975)MATH
3.
Zurück zum Zitat Stoltenberg-Hansen, V., Moldestad, J., Tucker, J.V.: Finite algorithmic procedures and computation theories. Math. Scand. 46, 77–94 (1980)MathSciNetCrossRefMATH Stoltenberg-Hansen, V., Moldestad, J., Tucker, J.V.: Finite algorithmic procedures and computation theories. Math. Scand. 46, 77–94 (1980)MathSciNetCrossRefMATH
5.
Zurück zum Zitat Lynch, N.A., Blum, E.K.: A difference in expressive power between flowcharts and recursion schemes. Math. Syst Theory 12(1), 205–211 (1979)MathSciNetCrossRefMATH Lynch, N.A., Blum, E.K.: A difference in expressive power between flowcharts and recursion schemes. Math. Syst Theory 12(1), 205–211 (1979)MathSciNetCrossRefMATH
6.
Zurück zum Zitat McCarthy, J.: A basis for a mathematical theory of computation. In: proceedings of the Western Joint Computer Conference, pp 225–238 (1961) McCarthy, J.: A basis for a mathematical theory of computation. In: proceedings of the Western Joint Computer Conference, pp 225–238 (1961)
7.
Zurück zum Zitat Moschovakis, Y.N.: Recursion and complexity. Lecture notes, UCLA (2015) Moschovakis, Y.N.: Recursion and complexity. Lecture notes, UCLA (2015)
8.
Zurück zum Zitat Moschovakis, Y.N., van den Dries, L.: Arithmetic complexity. ACM Trans. Comput. Log. 10 (2009) Moschovakis, Y.N., van den Dries, L.: Arithmetic complexity. ACM Trans. Comput. Log. 10 (2009)
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Zurück zum Zitat Paterson, M.S., Hewitt, C.E.: Comparative schematology. In: Proc. Rec. ACM Conference on Concurrent Systems and Parallel Computation, pp 119–127 (1970) Paterson, M.S., Hewitt, C.E.: Comparative schematology. In: Proc. Rec. ACM Conference on Concurrent Systems and Parallel Computation, pp 119–127 (1970)
11.
Zurück zum Zitat Tucker, J.V., Zucker, J.I.: Computable functions and semicomputable sets on many-sorted algebras, chapter 5, pages 397–525 Oxford University Press (2000) Tucker, J.V., Zucker, J.I.: Computable functions and semicomputable sets on many-sorted algebras, chapter 5, pages 397–525 Oxford University Press (2000)
Metadaten
Titel
A Difference in Complexity Between Recursion and Tail Recursion
verfasst von
Siddharth Bhaskar
Publikationsdatum
19.03.2016
Verlag
Springer US
Erschienen in
Theory of Computing Systems / Ausgabe 2/2017
Print ISSN: 1432-4350
Elektronische ISSN: 1433-0490
DOI
https://doi.org/10.1007/s00224-016-9673-5

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