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Papers by Mitsunori Ogihara

SIAM Journal on Computing, 1998

1. Introduction. The oracle separations proven by Baker, Gill, and Solovay [2] initiated the stud... more 1. Introduction. The oracle separations proven by Baker, Gill, and Solovay [2] initiated the study of complexity classes by relativization. Since that work, various relativization models for nondeterministic logspace have been introduced [13, 19, 16, 18]. Ladner and Lynch [13] and I. Simon [19] studied the models that allow oracle machines to make nondeterministic moves while generating query strings and to generate polynomially long query strings. Unfortunately, their models produce some counterintuitive results. With NL as the oracle, NL becomes NP while P remains P. ...

Electronic Colloquium on Computational Complexity - Reports Series 1996 - available via: FTP: ftp... more Electronic Colloquium on Computational Complexity - Reports Series 1996 - available via: FTP: ftp.eccc.uni-trier.de:/pub/eccc/ WWW: http://www.eccc.uni-trier.de/eccc/ Email: ftpmail@ftp.eccc.uni-trier.de with subject 'help eccc' ... Mitsunori Ogihara Department of Computer science University of Rochester Rochester, NY 14627 ... It is shown that the PL hierarchy ... PLH = PL J PL J PL J • • • ... The oracle separations proven by Baker, Gill, and Solovay [BGS75] initiated the study of complexity classes by relativization. In order to study the ...

Proceedings of the twenty-eighth annual ACM symposium on Theory of computing - STOC '96, 1996

Lecture Notes in Computer Science, 2005

Lecture Notes in Computer Science, 2000

Proceedings of IEEE 36th Annual Foundations of Computer Science, 1995

Abstract J. Hartmanis (1978) conjectured that there exist no sparse complete sets for P under log... more Abstract J. Hartmanis (1978) conjectured that there exist no sparse complete sets for P under logspace many-one reductions. In this paper, in support of the conjecture, it is shown that if P has sparse hard sets under logspace many-one reductions, then P⊆ DSPACE [log 2 n]. The result follows from a more general statement: if P has 2 polylog sparse hard sets under poly-logarithmic space-computable many-one reductions, then P⊆ DSPACE [polylog]

Advances in Algorithms, Languages, and Complexity, 1997

Abstract Sparse hard sets for complexity classes has been a central topic for two decades. The ar... more Abstract Sparse hard sets for complexity classes has been a central topic for two decades. The area is motivated by the desire to clarify relationships between completeness/hardness and density of languages and studies the existence of sparse complete/hard sets for various complexity classes under various reducibilities. Very recently, we have seen remarkable progress in this area for low-level complexity classes. In particular, the Hartmanis&amp;#x27; sparseness conjectures for P and NL have been resolved. This article overviews the ...

Lecture Notes in Computer Science, 2001

This paper presents an implementation of a concurrent version of Schöning&amp;amp;amp;amp... more This paper presents an implementation of a concurrent version of Schöning&amp;amp;amp;amp;#x27;s algorithm for k-SAT in [Sch99]. It is shown that the algorithm can be implemented with space complexity O ((2− 2/k) n) and time complexity O (kmn+ n 3), where n is the number of variables and m the number of clauses. Besides, borrowing ideas from the above mentioned implementation, it is presented an implementation of resolution, a widely studied and used proof system, mainly in the fields of Proof Complexity and Automated Theorem Proving.

International Journal of Foundations of Computer Science - IJFCS, 1994

Cai and Furst introduced the notion of bottleneck Turing machines and showed that thelanguages re... more Cai and Furst introduced the notion of bottleneck Turing machines and showed that thelanguages recognized by width-5 bottleneck Turing machines are exactly those in PSPACE.Computational power of bottleneck Turing machines with width fewer than 5 is investigated.It is shown that width-2 bottleneck Turing machines capture polynomial-time many-oneclosure of nearly near-testable sets. For languages recognized by bottleneck Turing machineswith intermediate width 3 and 4, some lower- and...

Theory of Computing Systems, 2010

Abstract In Loos and Ogihara (Theor. Comput. Sci., 386 (1-2): 132–150, 2007), time complexity for... more Abstract In Loos and Ogihara (Theor. Comput. Sci., 386 (1-2): 132–150, 2007), time complexity for splicing systems has been introduced. This paper further explores the time complexity for splicing systems and in addition defines a notion of space complexity, which is based on the description size of the production tree of a word. It is then shown that all languages accepted by t (n) space-bounded nondeterministic Turing machines can be generated by extended splicing systems with a regular set of rules in time O (t (n) 2). ...

Theoretical Computer Science, 2007

Theoretical Computer Science, 1998

SIAM Journal on Computing, 1995

Journal of Computer and System Sciences, 2004

Chicago Journal of Theoretical Computer Science - CJTCS, 1996

Theory of Computing Systems, 2003

Page 1. DOI: 10.1007/s00224-002-1079-x Theory Comput. Systems 36, 295–299 (2003) Theory of Comput... more Page 1. DOI: 10.1007/s00224-002-1079-x Theory Comput. Systems 36, 295–299 (2003) Theory of Computing Systems © 2003 Springer-Verlag New York Inc. A Note on Square Rooting of Time Functions of Turing Machines ∗ Richard J. Lipton,1 Mitsunori Ogihara,2 and Yechezkel Zalcstein1 1College of Computing, Georgia Institute of Technology, Atlanta, GA 30332, USA {rjl,zzalcste}@cc.gatech.edu 2Department of Computer Science, University of Rochester, Rochester, NY 14627-0226, USA ogihara@cs.rochester.edu 1. Introduction ...