Subanalytic solutions of linear difference equations and multidimensional hypergeometric sequences

  • Authors:
  • S. A. Abramov;M. A. Barkatou;M. van Hoeij;M. Petkovek

  • Affiliations:
  • Computing Centre of the Russian Academy of Sciences, Vavilova 40, Moscow 119333, GSP-1, Russia;Institute XLIM Université de Limoges, CNRS, 123, Av. A. Thomas, 87060 Limoges cedex, France;Florida State University, Department of Mathematics, Tallahassee, FL 32306-3027, USA;University of Ljubljana, Faculty of Mathematics and Physics, Jadranska 19, SI-1000 Ljubljana, Slovenia

  • Venue:
  • Journal of Symbolic Computation
  • Year:
  • 2011

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Abstract

We consider linear difference equations with polynomial coefficients over C and their solutions in the form of sequences indexed by the integers (sequential solutions). We investigate the C-linear space of subanalytic solutions, i.e., those sequential solutions that are the restrictions to Z of some analytic solutions of the original equation. It is shown that this space coincides with the space of the restrictions to Z of entire solutions and that the dimension of this space is equal to the order of the original equation. We also consider d-dimensional (d=1) hypergeometric sequences, i.e., sequential and subanalytic solutions of consistent systems of first-order difference equations for a single unknown function. We show that the dimension of the space of subanalytic solutions is always at most 1, and that this dimension may be equal to 0 for some systems (although the dimension of the space of all sequential solutions is always positive). Subanalytic solutions have applications in computer algebra. We show that some implementations of certain well-known summation algorithms in existing computer algebra systems work correctly when the input sequence is a subanalytic solution of an equation or a system, but can give incorrect results for some sequential solutions.