An analog characterization of the Grzegorczyk hierarchy

  • Authors:
  • Manuel Lameiras Campagnolo;Cristopher Moore;José/ Fé/lix Costa

  • Affiliations:
  • D.M.II.S.A., Universidade Té/cnica de Lisboa, Tapada da Ajuda, 1349-017 Lisboa, Portugal;Santa Fe Institute, 1399 Hyde Park Road, Santa Fe, New Mexico 87501/ Computer Science Department, University of New Mexico, Albuquerque, New Mexico 87131/ and Physics Department, University of New ...;D.M.II.S T., Universidade Té/cnica de Lisboa, Av. Rovisco Pais. 1049-001 Lisboa, Portugal

  • Venue:
  • Journal of Complexity
  • Year:
  • 2002

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Abstract

We study a restricted version of Shannon's general purpose analog computer in which we only allow the machine to solve linear differential equations. We show that if this computer is allowed to sense inequalities in a differentiable way, then it can compute exactly the elementary functions, the smallest known recursive class closed under time and space complexity. Furthermore, we show that if the machine has access to a function f(x) with a suitable growth as x goes to infinity, then it can compute functions on any given level of the Grzegorczyk hierarchy. More precisely, we show that the model contains exactly the nth level of the Grzegorczyk hierarchy if it is allowed to solve n - 3 non-linear differential equations of a certain kind. Therefore, we claim that, at least in this region of the complexity hierarchy, there is a close connection between analog complexity classes, the dynamical systems that compute them, and classical sets of subrecursive functions.