<p>We introduce radial variants of the Wijsman and Attouch-Wets topologies for the family <InlineEquation ID="IEq1"> <EquationSource Format="MATHML"><math> <msubsup> <mi mathvariant="script">S</mi> <mrow> <mi>r</mi> <mi>c</mi> </mrow> <mi>d</mi> </msubsup> </math></EquationSource> <EquationSource Format="TEX">$\mathcal{S}_{rc}^{d}$</EquationSource> </InlineEquation> of star-shaped sets (with respect to the origin) in <InlineEquation ID="IEq2"> <EquationSource Format="MATHML"><math> <msup> <mi mathvariant="double-struck">R</mi> <mi>d</mi> </msup> </math></EquationSource> <EquationSource Format="TEX">$\mathbb{R}^{d}$</EquationSource> </InlineEquation> that are radially closed. These topologies give rise to new types of convergence for star-shaped sets, even when such sets are not closed or bounded. Our approach relies on a new family of functionals, called <i>radial distance functionals</i>, which measure “radial distances” between points and star-shaped sets in <InlineEquation ID="IEq3"> <EquationSource Format="MATHML"><math> <msubsup> <mi mathvariant="script">S</mi> <mrow> <mi>r</mi> <mi>c</mi> </mrow> <mi>d</mi> </msubsup> </math></EquationSource> <EquationSource Format="TEX">$\mathcal{S}_{rc}^{d}$</EquationSource> </InlineEquation>. These are natural radial analogues of the distance functionals for closed sets. However, unlike the radial functions of star-shaped sets, our radial distance functionals are real-valued maps and thus admit a natural treatment within the framework of classical function spaces. We prove that our radial Wijsman type topology <InlineEquation ID="IEq4"> <EquationSource Format="MATHML"><math> <msub> <mi>τ</mi> <msup> <mi>W</mi> <mi>r</mi> </msup> </msub> </math></EquationSource> <EquationSource Format="TEX">$\tau _{W^{r}}$</EquationSource> </InlineEquation> is not metrizable on <InlineEquation ID="IEq5"> <EquationSource Format="MATHML"><math> <msubsup> <mi mathvariant="script">S</mi> <mrow> <mi>r</mi> <mi>c</mi> </mrow> <mi>d</mi> </msubsup> </math></EquationSource> <EquationSource Format="TEX">$\mathcal{S}_{rc}^{d}$</EquationSource> </InlineEquation>, while our radial Attouch-Wets type topology <InlineEquation ID="IEq6"> <EquationSource Format="MATHML"><math> <msub> <mi>τ</mi> <mrow> <mi>A</mi> <msup> <mi>W</mi> <mi>r</mi> </msup> </mrow> </msub> </math></EquationSource> <EquationSource Format="TEX">$\tau _{AW^{r}}$</EquationSource> </InlineEquation> is completely metrizable. A corresponding radial Attouch-Wets distance <InlineEquation ID="IEq7"> <EquationSource Format="MATHML"><math> <msub> <mi>d</mi> <mrow> <mi>A</mi> <msup> <mi>W</mi> <mi>r</mi> </msup> </mrow> </msub> </math></EquationSource> <EquationSource Format="TEX">$d_{AW^{r}}$</EquationSource> </InlineEquation> is introduced, and we prove that <InlineEquation ID="IEq8"> <EquationSource Format="MATHML"><math> <msub> <mi>d</mi> <mrow> <mi>A</mi> <mi>W</mi> </mrow> </msub> <mo stretchy="false">(</mo> <mi>A</mi> <mo>,</mo> <mi>K</mi> <mo stretchy="false">)</mo> <mo>≤</mo> <msub> <mi>d</mi> <mrow> <mi>A</mi> <msup> <mi>W</mi> <mi>r</mi> </msup> </mrow> </msub> <mo stretchy="false">(</mo> <mi>A</mi> <mo>,</mo> <mi>K</mi> <mo stretchy="false">)</mo> </math></EquationSource> <EquationSource Format="TEX">$d_{AW}(A,K) \leq d_{AW^{r}}(A,K)$</EquationSource> </InlineEquation> for all closed <InlineEquation ID="IEq9"> <EquationSource Format="MATHML"><math> <mi>A</mi> <mo>,</mo> <mi>K</mi> <mo>∈</mo> <msubsup> <mi mathvariant="script">S</mi> <mrow> <mi>r</mi> <mi>c</mi> </mrow> <mi>d</mi> </msubsup> </math></EquationSource> <EquationSource Format="TEX">$A,K \in \mathcal{S}_{rc}^{d}$</EquationSource> </InlineEquation>, where <InlineEquation ID="IEq10"> <EquationSource Format="MATHML"><math> <msub> <mi>d</mi> <mrow> <mi>A</mi> <mi>W</mi> </mrow> </msub> </math></EquationSource> <EquationSource Format="TEX">$d_{AW}$</EquationSource> </InlineEquation> denotes the Attouch-Wets distance.</p>

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New Types of Convergence for Unbounded Star-Shaped Sets

  • Luisa F. Higueras-Montaño

摘要

We introduce radial variants of the Wijsman and Attouch-Wets topologies for the family S r c d $\mathcal{S}_{rc}^{d}$ of star-shaped sets (with respect to the origin) in R d $\mathbb{R}^{d}$ that are radially closed. These topologies give rise to new types of convergence for star-shaped sets, even when such sets are not closed or bounded. Our approach relies on a new family of functionals, called radial distance functionals, which measure “radial distances” between points and star-shaped sets in S r c d $\mathcal{S}_{rc}^{d}$ . These are natural radial analogues of the distance functionals for closed sets. However, unlike the radial functions of star-shaped sets, our radial distance functionals are real-valued maps and thus admit a natural treatment within the framework of classical function spaces. We prove that our radial Wijsman type topology τ W r $\tau _{W^{r}}$ is not metrizable on S r c d $\mathcal{S}_{rc}^{d}$ , while our radial Attouch-Wets type topology τ A W r $\tau _{AW^{r}}$ is completely metrizable. A corresponding radial Attouch-Wets distance d A W r $d_{AW^{r}}$ is introduced, and we prove that d A W ( A , K ) d A W r ( A , K ) $d_{AW}(A,K) \leq d_{AW^{r}}(A,K)$ for all closed A , K S r c d $A,K \in \mathcal{S}_{rc}^{d}$ , where d A W $d_{AW}$ denotes the Attouch-Wets distance.