Space of continuous set-valued mappings with closed unbounded values
A. A. Tolstonogov Matrosov Institute for System Dynamics and Control Theory of Siberian Branch of Russian Academy of Sciences, Irkutsk
Abstract:
We consider a space of continuous multivalued mappings defined on a locally compact space
${\mathcal T}$ with countable base. Values of these mappings are closed not necessarily bounded sets from a metric space
$(X,d(\cdot))$ in which closed balls are compact. The space
$(X,d(\cdot))$ is locally compact and separable. Let
$Y$ be a dense countable set from
$X$. The distance
$\rho(A,B)$ between sets
$A$ and
$B$ from the family
$CL(X)$ of all nonempty closed subsets of
$X$ is defined as
$$\rho(A,B)=\sum_{i=1}^\infty \frac{1}{2^i}\,\frac{\mid~d(y_i,A)-d(y_i,B)\mid}{1+\mid~d(y_i,A)-d(y_i,B)\mid},$$
where
$d(y_i,A)$ is the distance from a point
$y_i \in Y$ to the set
$A$. This distance is independent of the choice of the set
$Y$, and the function
$\rho(A,B)$ is a metric on the space
$CL(X)$. The convergence of a sequence of sets
$A_n$,
$n\ge 1$, from the metric space
$(CL(X),\rho(\cdot))$ is equivalent to the Kuratowski convergence of this sequence. We prove the completeness and separability of the space
$(CL(X),\rho (\cdot))$ and give necessary and sufficient conditions for the compactness of sets in this space. The space
$C({\mathcal T}, CL(X))$ of all continuous mappings from
${\mathcal T}$ to
$(CL(X),\rho (\cdot))$ is endowed with the topology of uniform convergence on compact sets from
${\mathcal T}$. We prove the completeness and separability of the space
$C({\mathcal T}, CL(X))$ and give necessary and sufficient conditions for the compactness of sets in this space. These results are reformulated for the space
$C(T,CCL(X))$, where
$T=[0,1]$,
$X$ is a finite-dimensional Euclidean space, and
$CCL(X)$ is the space of all nonempty closed convex sets from
$X$ with the metric
$\rho(\cdot)$. This space plays a crucial role in the study of sweeping processes. A counterexample showing the significance of the assumption of the compactness of closed balls from
$X$ is given.
Keywords:
unbounded sets, Kuratowski convergence, compactness.
UDC:
515.126.83
MSC: 58C06 Received: 25.09.2017
DOI:
10.21538/0134-4889-2018-24-1-200-208