# Polynomial interpolation and a priori bootstrap for computer-assisted proofs in nonlinear ODEs

## TL;DR

This paper introduces a rigorous computational method using polynomial interpolation and a priori bootstrap to prove existence of solutions and special orbits in nonlinear ODEs, demonstrated on Lorenz and ABC flow systems.

## Contribution

It develops a novel a priori bootstrap technique combined with a fixed point approach for computer-assisted proofs in nonlinear ODEs.

## Key findings

- Proved existence of solutions for Lorenz system at classical parameters.
- Established existence of ballistic spiral orbits in ABC flows.
- Validated the method on complex nonlinear systems.

## Abstract

In this work, we introduce a method based on piecewise polynomial interpolation to enclose rigorously solutions of nonlinear ODEs. Using a technique which we call a priori bootstrap, we transform the problem of solving the ODE into one of looking for a fixed point of a high order smoothing Picard-like operator. We then develop a rigorous computational method based on a Newton-Kantorovich type argument (the radii polynomial approach) to prove existence of a fixed point of the Picard-like operator. We present all necessary estimates in full generality and for any nonlinearities. With our approach, we study two systems of nonlinear equations: the Lorenz system and the ABC flow. For the Lorenz system, we solve Cauchy problems and prove existence of periodic and connecting orbits at the classical parameters, and for ABC flows, we prove existence of ballistic spiral orbits.