Research

A 2014 version of my research can be found in my habilitation manuscrit.

I am interested in formal proofs aboput numerical analysis. See the FOST project page for the verification of a program implementing a 1D-wave equation approximation scheme. See also Coq proof of the Lax-Milgram theorem.

I am also interested in the formal verification of numerical programs.

Gallery of proved programs:

The verification of these programs is currently redone. This is why I only give the C programs, without their proof at the moment. Contact me if you need some old proofs.

Floating-point tricks

This means floating-point arithmetic specificities are heavily used in these programs.

  • Sterbenz
    This function computes the exact subtraction if the inputs are near enough one to another.
    C code
  • Malcolm
    This function computes the radix of the computations. Here in IEEE-754 double precision, the result is 2. But I like the while (A != (A+1)) loop.
    C code
  • Dekker
    This function computes the exact error of the multiplication (with Underflow restrictions). There are also Overflow restrictions so that no infinity will be created.
    C code

Floating-point handling

This means that these programs would give the correct answer if real arithmetic was used, but floating-point properties are needed to prove their accuracy and that no exceptional behavior occur.

  • Average, Sterbenz's version
    This function computes an approximation of the average of two floating-point numbers. It was written using hints given by Sterbenz in order to prevent overflow. Accuracy is 3/2 ulp.
    C code
  • Average, correct version
    This function computes the correct rounding of the average of two floating-point numbers. It gives the perfect value, while preventing overflows.
    C code
  • Discriminant
    This function computes an accurate discriminant using Kahan's algorithm. The result is proved correct within 2 ulps. Overflow and Underflow restrictions are given.
    C code
  • Triangle
    This function computes the area of a triangle, even if the triangle is needle-like. The algorithm is due to Kahan. The error bound is improved on Goldberg's and overflow and underflow restrictions are given.
    C code

Numerical analysis
  • rec_lin2
    This example was developed among the FOST project. This very simple code is a linear recurrence of order 2.
    C code
  • dirichlet
    This example was developed among the FOST project. It is a finite difference numerical scheme for the resolution of the one-dimensional acoustic wave equation. A reasonable bound on the rounding error requires a complex property that expresses each rounding error. The bound on the method error of this scheme has also been formally certified in Coq. For this proof, we also require the Coquelicot Coq library.
    C code
Avionics
  • eps_line1
    This example is part of KB3D, an aircraft conflict detection and resolution program. The aim is to make a decision corresponding to value -1 and 1 to decide if the plane will go to its left or its right. Note that KB3D is formally proved correct using PVS and assuming the calculations are exact. However, in practice, when the value of the computation is small, the result may be inconsistent or incorrect. The proofs are here fully automatic.
    C code
  • eps_line2
    This is the same example as eps_line1 except that we are independent from the execution hardware and the compilation choices (extended registers, FMA).
    C code