Fourier-Taylor Parameterization of Unstable Manifolds for Parabolic Partial Differential Equations: Formalization, Implementation, and Rigorous Validation

TL;DR

This paper introduces a Fourier-Taylor parameterization method for high-order expansions of unstable manifolds in parabolic PDEs, combining formal series, numerical computation, and rigorous validation to analyze local dynamics near equilibria.

Contribution

It formalizes and implements a novel Fourier-Taylor approach for unstable manifolds of parabolic PDEs, including convergence proofs and computer-assisted validation.

Findings

Successfully computed high-order unstable manifolds for Fisher's equation

Validated convergence of formal series expansions numerically

Provided a computer-assisted proof of a heteroclinic orbit

Abstract

In this paper we study high order expansions of chart maps for local finite dimensional unstable manifolds of hyperbolic equilibrium solutions of scalar parabolic partial differential equations. Our approach is based on studying an infinitesimal invariance equation for the chart map that recovers the dynamics on the manifold in terms of a simple conjugacy. We develop formal series solutions for the invariance equation and efficient numerical methods for computing the series coefficients to any desired finite order. We show, under mild non-resonance conditions, that the formal series expansion converges in a small enough neighborhood of the equilibrium. An a-posteriori computer assisted argument proves convergence in larger neighborhoods. We implement the method for a spatially inhomogeneous Fisher's equation and numerically compute and validate high order expansions of some local unstable manifolds for morse index one and two. We also provide a computer assisted existence proof of a saddle-to-sink heteroclinic connecting orbit.