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Let

  • $E$ be a locally compact separable metric space
  • $(\mathcal D(A),A)$ be the generator of a strongly continuous contraction semigroup on $C_0(E)$
  • $E_n$ be a metric space for $n\in\mathbb N$
  • $(\mathcal D(A_n),A_n)$ be the generator of a strongly continuous contraction semigroup on$^1$ $B(E_n)$
  • $\pi_n:E_n\to E$ be continuous and $$\iota_nf:=f\circ\pi_n\;\;\;\text{for }f\in C_0(E)$$ for $n\in\mathbb N$

Let $\lambda>0$ and $f\in C_0(E)$. Assume$^2$ $$\left|\left(R_\lambda(A_n)\iota_nf\right)(x_n)-\left(R_\lambda(A)f\right)(x)\right|\xrightarrow{n\to\infty}0\tag1$$ for all $x_n\in E_n$, $n\in\mathbb N$, and $x\in E$ with $\pi_n(x_n)\xrightarrow{n\to\infty}x$. Are we able to conclude $$\left\|R_\lambda(A_n)\iota_nf-\iota_nR_\lambda(A)f\right\|_\infty\xrightarrow{n\to\infty}0;\tag2$$ at least under suitable further assumptions (e.g. compactness of $E$)?

Note that the result holds if $E_n=E$ for all $n\in\mathbb N$, $E$ is compact and $\iota_n$ is the identity for all $n\in\mathbb N$: https://math.stackexchange.com/q/3139957/47771.

We may note that by contractivity, $(0,\infty)$ is contained in the resolvent sets of $(\mathcal D(A_n),A_n)$, $n\in\mathbb N$, and $(\mathcal D(A),A)$. Moreover, $$\left\|R_\lambda(A_n)\right\|,\left\|R_\lambda(A)\right\|\le\frac1\lambda\;\;\;\text{for all }n\in\mathbb N.\tag3$$ This might be crucial.


$^1$ If $S$ is a set, let $B(S)$ denote the space of bounded functions from $S$ to $\mathbb R$ equipped with the supremum norm.

$^2$ If $(\mathcal D(B),B)$ is a bounded linear operator on a Banach space and $\lambda$ is a regular value of $(\mathcal D(B),B)$, let $R_\lambda(B)$ denote the resolvent operator of $(\mathcal D(B),B)$.

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  • $\begingroup$ There are no $C_0$-semigroups (except for those with bounded generator) on $B(E_n)$, so I'm a bit confused by your fourth assumption. $\endgroup$ Commented May 23, 2019 at 9:56
  • $\begingroup$ @JochenGlueck I didn't know that (do you have a reference?), but it shouldn't matter for the question. However, the $C_0$-semigroups I've got in mind for my application do actually have bounded generators. $\endgroup$
    – 0xbadf00d
    Commented May 23, 2019 at 10:14
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    $\begingroup$ The result I mentioned can for instance be found in Theorem A-II-3.6 of "R. Nagel (ed.): One-parameter Semigroups of Positive Operators (Springer, 1986)". $\endgroup$ Commented May 23, 2019 at 19:35
  • $\begingroup$ @JochenGlueck Do you know whether this is still true when we replace $B(E_n)$ by the closed sbuspace of bounded Borel measurable functions? $\endgroup$
    – 0xbadf00d
    Commented May 27, 2019 at 17:02
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    $\begingroup$ Yes, it is also true on the space of bounded measurable functions on any given measurable space; this is assertion 3) of the reference I quoted above (while the result on $B(E_n)$ is a special case of assertion 2) there). By the way, you can download this book from the homepage of its editor Rainer Nagel. $\endgroup$ Commented May 28, 2019 at 19:49

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