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 Title: Computational complexity of random-access models Author(s): Luginbuhl, David Ralph Doctoral Committee Chair(s): Loui, Michael C. Department / Program: Computer Science Discipline: Computer Science Degree Granting Institution: University of Illinois at Urbana-Champaign Degree: Ph.D. Genre: Dissertation Subject(s): Mathematics Computer Science Abstract: The relative power of several computational models is considered. These models are the Turing machine and its multidimensional variant, the random access machine (RAM), the tree machine, and the pointer machine. The basic computational properties of the pointer machine are examined in more detail. For example, time and space hierarchy theorems for pointer machines are presented.Every Turing machine of time complexity $t$ and space complexity $s$ can be simulated by a pointer machine of time complexity $O$($t$) using $O$($s$/log $s$) nodes. This strengthens a similar result by van Emde Boas (1989). Every alternating pointer machine of time complexity $t$ can be simulated by a deterministic pointer machine using $O$($t$/log $t$) nodes. Other results concerning nondeterministic and alternating pointer machines are presented.Every tree machine of time complexity $t$ can be simulated on-line by a log-cost RAM of time complexity $O$(($t$log $t$)/log log $t$). This simulation is shown to be optimal using the notion of incompressibility from Kolmogorov complexity (Solomonoff, 1964; Kolmogorov, 1965).Every $d$-dimensional Turing machine of time complexity $t$ can be simulated on-line by a log-cost RAM running in time $O$($t$(log $t$)$\sp{1-(1/d)}$)(log log $t$)$\sp{(1/d}$). There is a log-cost RAM $R$ running in time $t$ such that every $d$-dimensional Turing machine requires time $\Omega$($t\sp{1+(1/d)}$/(log $t$(log log $t$)$\sp{1+(1/d)}$)) to simulate $R$ on-line. Every unit-cost RAM of time complexity $t$ can be simulated on-line by a $d$-dimensional Turing machine in time $O$($t$($n$)$\sp2$log $t$($n$)). Issue Date: 1990 Type: Text Language: English URI: http://hdl.handle.net/2142/22763 Rights Information: Copyright 1990 Luginbuhl, David Ralph Date Available in IDEALS: 2011-05-07 Identifier in Online Catalog: AAI9026259 OCLC Identifier: (UMI)AAI9026259
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