On evolution equations governed by non-autonomous forms

Abstract

We consider a linear non-autonomous evolutionary Cauchy problem \begin{equation} \dot{u} (t)+A(t)u(t)=f(t) \hbox{ for }\ \hbox{a.e. t}\in [0,T],\quad u(0)=u_0, \end{equation} where the operator $A(t)$ arises from a time depending sesquilinear form $a(t,.,.)$ on a Hilbert space $H$ with constant domain $V.$ Recently a result on $L^2$-maximal regularity in $H,$ i.e., for each given $f\in L^2(0,T,H)$ and $u_0 \in V$ the problem above has a unique solution $u\in L^2(0,T,V)\cap H^1(0,T,H),$ is proved in [10] under the assumption that $a$ is symmetric and of bounded variation. The aim of this paper is to prove that the solutions of an approximate non-autonomous Cauchy problem in which $a$ is symmetric and piecewise affine are closed to the solutions of that governed by symmetric and of bounded variation form. In particular, this provide an alternative proof of the result in [10] on $L^2$-maximal regularity in $H.$