Representation of solutions to wave equations with profile functions

Abstract

Solutions to the wave equation with constant coefficients in ${\mathbb{R}}^d$ can be represented explicitly in Fourier space. We investigate a reconstruction formula, which provides an approximation of solutions $u(.,t)$ to initial data $u_0(.)$ for large times. The reconstruction consists of three steps: 1) Given $u_0$, initial data for a profile equation are extracted. 2) A profile evolution equation determines the shape of the profile at time $\tau ={\epsilon }^{2}t$. 3) A shell reconstruction operator transforms the profile to a function on ${\mathbb{R}}^d$. The sketched construction simplifies the wave equation, since only a one-dimensional problem in an $O(1)$ time span has to be solved. We prove that the construction provides a good approximation to the wave evolution operator for times $t$ of order ${\epsilon }^{-2}$.