Functions computable in polynomial space

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Abstract

Consider nondeterministic polynomial-time Turing machine that on input x outputs a 3 × 3 matrix with entries from {−1, 0, 1} on each of its paths. Define the function f where f (x) is the upper left entry in the product of all these matrices (in an order of the paths to be made precise below). We show that the class of functions f computable as just described is exactly the class FPSPACE of integer-valued functions computable by polynomial-space Turing machines. Along the way we obtain characterizations of FPSPACE in terms of arithmetic circuits and straight-line programs.

MSC

68Q10
68Q15
68Q05

Keywords

Polynomial space
Complexity class of functions
Bottleneck machines
Leaf languages
Arithmetic circuits
Straight-line programs

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