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Unformatted text preview: CS 373: Theory of Computation Gul Agha Mahesh Viswanathan Fall 2010 1 1 Unrestricted Computation General Computing Machines Machines so far: DFAs, NFAs, GNFAs Limitations on how much memory they can use: fixed amount of memory Limitations on what they can compute/decide: only regular languages The complete machine? No limitations on memory usage? And maybe other ways to use computational resources that we havent thought of... * Come up with a model that describes all conceivable computation No limitation on what they can compute? * No! There are far too many languages over { , 1 } than there are machines or programs (as long as machines can be represented digitally) General Computing Machines Alonzo Church, Emil Post, and Alan Turing (1936) Figure 1: Alonzo Church Figure 2: Emil Post 2 Figure 3: Alan Turing Church ( calculus), Post (Posts machine), Turing (Turing machine) independently came up with formal definitions of mechanical computation All equivalent! In this course: Turing Machines 2 Turing Machines 2.1 Definition The aha moment Figure 4: Turing Machines 3 X 1 X 2 X n t t finitestate control tape head Unrestricted memory: an infinite tape A finite state machine that reads/writes symbols on the tape Can read/write anywhere on the tape Tape is infinite in one direction only (other variants possible) Initially, tape has input and the machine is reading (i.e., tape head is on) the leftmost input symbol. Transition (based on current state and symbol under head): Change control state Overwrite a new symbol on the tape cell under the head Move the head left, or right....
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This note was uploaded on 10/04/2011 for the course CS 373 taught by Professor Viswanathan,m during the Fall '08 term at University of Illinois, Urbana Champaign.
 Fall '08
 Viswanathan,M

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