Krasnosel'skii type formula and translation along trajectories method for evolution equations

TL;DR

This paper establishes a Krasnosel'skii type degree formula for evolution equations involving a linear operator and a Lipschitz contraction, linking topological degree with fixed point index, and applies it to periodic problems and PDE systems.

Contribution

It introduces a new degree formula for evolution equations with Lipschitz nonlinearities, enhancing the translation along trajectories method.

Findings

Degree formula connects topological degree with fixed point index.

Applied to nonautonomous periodic problems.

Derived an average principle for evolution equations.

Abstract

The Krasnosel'skii type degree formula for the equation $\dot u = - Au + F(u)$ where $A:D(A)\to E$ is a linear operator on a separable Banach space $E$ such that $-A$ is a generator of a $C_0$ semigroup of bounsed linear operators of $E$ and $F:E\to E$ is a locally Lipschitz $k$-set contraction, is provided. Precisely, it is shown that if $V$ is an open bounded subset of $E$ such that $0\not\in (-A+F)(\partial V \cap D(A))$, then the topological degree of $-A+F$ with respect to $V$ is equal to the fixed point index of the operator of translation along trajectories for sufficiently small positive time. The obtained degree formula is crucial for the method of translation along trajctories. It is applied to the nonautonomous periodic problem and an average principle is derived. As an application a first order system of partial differential equations is considered.