Verified Real Number Calculations: A Library for Interval Arithmetic

  • Authors:
  • Marc Daumas;David Lester;Céar Muñoz

  • Affiliations:
  • ELIAUS, UPVD, Perpignan;University of Manchester, Manchester;National Institute of Aerospace, Hampton

  • Venue:
  • IEEE Transactions on Computers
  • Year:
  • 2009

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Abstract

Real number calculations on elementary functions are remarkably difficult to handle in mechanical proofs. In this paper, we show how these calculations can be performed within a theorem prover or proof assistant in a convenient and highly automated as well as interactive way. First, we formally establish upper and lower bounds for elementary functions. Then, based on these bounds, we develop a rational interval arithmetic where real number calculations take place in an algebraic setting. In order to reduce the dependency effect of interval arithmetic, we integrate two techniques: interval splitting and Taylor series expansions. This pragmatic approach has been developed, and formally verified, in a theorem prover. The formal development also includes a set of customizable strategies to automate proofs involving explicit calculations over real numbers. Our ultimate goal is to provide guaranteed proofs of numerical properties with minimal human theorem-prover interaction.