Formal Verification of Exact Computations Using Newton's Method

  • Authors:
  • Nicolas Julien;Ioana Paşca

  • Affiliations:
  • INRIA Sophia Antipolis,;INRIA Sophia Antipolis,

  • Venue:
  • TPHOLs '09 Proceedings of the 22nd International Conference on Theorem Proving in Higher Order Logics
  • Year:
  • 2009

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Abstract

We are interested in the verification of Newton's method. We use a formalization of the convergence and stability of the method done with the axiomatic real numbers of Coq's Standard Library in order to validate the computation with Newton's method done with a library of exact real arithmetic based on co-inductive streams. The contribution of this work is twofold. Firstly, based on Newton's method, we design and prove correct an algorithm on streams for computing the root of a real function in a lazy manner. Secondly, we prove that rounding at each step in Newton's method still yields a convergent process with an accurate correlation between the precision of the input and that of the result. An algorithm including rounding turns out to be much more efficient.