Trusting Computations: a Mechanized Proof from Partial Differential Equations to Actual Program
For developers of scientific computing software, this work demonstrates that full formal verification of numerical programs is feasible, addressing the problem of trusting computations.
The authors mechanically verified the convergence of a numerical scheme for solving the 1D wave equation, producing a complete formal proof from partial differential equations to actual numerical results. This is the first time such a comprehensive proof has been achieved.
Computer programs may go wrong due to exceptional behaviors, out-of-bound array accesses, or simply coding errors. Thus, they cannot be blindly trusted. Scientific computing programs make no exception in that respect, and even bring specific accuracy issues due to their massive use of floating-point computations. Yet, it is uncommon to guarantee their correctness. Indeed, we had to extend existing methods and tools for proving the correct behavior of programs to verify an existing numerical analysis program. This C program implements the second-order centered finite difference explicit scheme for solving the 1D wave equation. In fact, we have gone much further as we have mechanically verified the convergence of the numerical scheme in order to get a complete formal proof covering all aspects from partial differential equations to actual numerical results. To the best of our knowledge, this is the first time such a comprehensive proof is achieved.