2005 | OriginalPaper | Buchkapitel
A Tight Linear Bound on the Neighborhood of Inverse Cellular Automata
verfasst von : Eugen Czeizler, Jarkko Kari
Erschienen in: Automata, Languages and Programming
Verlag: Springer Berlin Heidelberg
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Reversible cellular automata (RCA) are models of massively parallel computation that preserve information. They consist of an array of identical finite state machines that change their states synchronously according to a local update rule. By selecting the update rule properly the system has been made information preserving, which means that any computation process can be traced back step-by-step using an inverse automaton. We investigate the maximum range in the array that a cell may need to see in order to determine its previous state. We provide a tight upper bound on this inverse neighborhood size in the one-dimensional case: we prove that in a RCA with
n
states the inverse neighborhood is not wider than
n
–1, when the neighborhood in the forward direction consists of two consecutive cells. Examples are known where range
n
–1 is needed, so the bound is tight. If the forward neighborhood consists of
m
consecutive cells then the same technique provides the upper bound
n
m
− 1
–1 for the inverse direction.