Characterizations of the Crandall--Pazy Class of $C_0$-semigroups on Hilbert Spaces and Their Application to Decay Estimates

TL;DR

This paper characterizes the Crandall--Pazy class of $C_0$-semigroups on Hilbert spaces and applies these results to derive decay estimates for numerical schemes solving stable abstract Cauchy problems.

Contribution

It provides two new characterizations of the Crandall--Pazy class in Hilbert spaces and uses them to improve decay estimates for numerical schemes.

Findings

Two characterizations of the Crandall--Pazy class are established.

Decay estimates for Crank--Nicolson schemes are improved using these characterizations.

Additional assumptions lead to better decay bounds via Lyapunov equations.

Abstract

We investigate immediately differentiable $C_0$-semigroups $(e^{-tA})_{t \geq 0}$ satisfying $\sup_{0 < t <1} t^{1/\beta}\|Ae^{-tA}\| < \infty$ for some $0 < \beta \leq 1$. Such $C_0$-semigroups are referred to as the Crandall--Pazy class of $C_0$-semigroups. In the Hilbert space setting, we present two characterizations of the Crandall--Pazy class. We then apply these characterizations to estimate decay rates for Crank--Nicolson schemes with smooth initial data when the associated abstract Cauchy problem is governed by an exponentially stable $C_0$-semigroup in the Crandall--Pazy class. The first approach is based on a functional calculus called the $\mathcal{B}$-calculus. The second approach builds upon estimates derived from Lyapunov equations and improves the decay estimate obtained in the first approach, under the additional assumption that $-A^{-1}$ generates a bounded $C_0$-semigroup.