<p>In this article, our main goal is to extend the concept of dynamical sampling to quaternionic Hilbert spaces. The problem is to recover the initial state of an evolving function <InlineEquation ID="IEq1"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="40863_2025_496_Article_IEq1.gif" Format="GIF" Height="17" Rendition="HTML" Resolution="72" Type="Linedraw" Width="7" /> </InlineMediaObject> <EquationSource Format="TEX">\(\mathfrak {f}\)</EquationSource> <EquationSource Format="MATHML"><math> <mi mathvariant="fraktur">f</mi> </math></EquationSource> </InlineEquation> from the system <InlineEquation ID="IEq2"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="40863_2025_496_Article_IEq2.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="242" /> </InlineMediaObject> <EquationSource Format="TEX">\(\mathcal {T}:=\{T^{n}\mathfrak {f}(m):n\in \Omega _m\text {, }m\in \mathcal {J}\}\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi mathvariant="script">T</mi> <mo>:</mo> <mo>=</mo> <mo stretchy="false">{</mo> <msup> <mi>T</mi> <mi>n</mi> </msup> <mi mathvariant="fraktur">f</mi> <mrow> <mo stretchy="false">(</mo> <mi>m</mi> <mo stretchy="false">)</mo> </mrow> <mo>:</mo> <mi>n</mi> <mo>∈</mo> <msub> <mi mathvariant="normal">Ω</mi> <mi>m</mi> </msub> <mtext>,</mtext> <mspace width="0.333333em" /> <mi>m</mi> <mo>∈</mo> <mi mathvariant="script">J</mi> <mo stretchy="false">}</mo> </mrow> </math></EquationSource> </InlineEquation> of its spatial sampling taken at different time levels <i>n</i>, where <InlineEquation ID="IEq3"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="40863_2025_496_Article_IEq3.gif" Format="GIF" Height="15" Rendition="HTML" Resolution="72" Type="Linedraw" Width="17" /> </InlineMediaObject> <EquationSource Format="TEX">\(\mathcal {J}\)</EquationSource> <EquationSource Format="MATHML"><math> <mi mathvariant="script">J</mi> </math></EquationSource> </InlineEquation> is an index set and <InlineEquation ID="IEq4"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="40863_2025_496_Article_IEq4.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="151" /> </InlineMediaObject> <EquationSource Format="TEX">\(\Omega _m=\{0\text {, }1\text {,}\dots \text {, }k_m\}\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi mathvariant="normal">Ω</mi> <mi>m</mi> </msub> <mo>=</mo> <mrow> <mo stretchy="false">{</mo> <mn>0</mn> <mtext>,</mtext> <mspace width="0.333333em" /> <mn>1</mn> <mtext>,</mtext> <mo>⋯</mo> <mtext>,</mtext> <mspace width="0.333333em" /> <msub> <mi>k</mi> <mi>m</mi> </msub> <mo stretchy="false">}</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation>. Initially the finite dimensional case for <InlineEquation ID="IEq5"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="40863_2025_496_Article_IEq5.gif" Format="GIF" Height="17" Rendition="HTML" Resolution="72" Type="Linedraw" Width="22" /> </InlineMediaObject> <EquationSource Format="TEX">\(\mathbb {H}^d\)</EquationSource> <EquationSource Format="MATHML"><math> <msup> <mrow> <mi mathvariant="double-struck">H</mi> </mrow> <mi>d</mi> </msup> </math></EquationSource> </InlineEquation> is studied and some characterizations for the system <InlineEquation ID="IEq6"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="40863_2025_496_Article_IEq6.gif" Format="GIF" Height="14" Rendition="HTML" Resolution="72" Type="Linedraw" Width="14" /> </InlineMediaObject> <EquationSource Format="TEX">\(\mathcal {T}\)</EquationSource> <EquationSource Format="MATHML"><math> <mi mathvariant="script">T</mi> </math></EquationSource> </InlineEquation> to form a frame for <InlineEquation ID="IEq7"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="40863_2025_496_Article_IEq5.gif" Format="GIF" Height="17" Rendition="HTML" Resolution="72" Type="Linedraw" Width="22" /> </InlineMediaObject> <EquationSource Format="TEX">\(\mathbb {H}^d\)</EquationSource> <EquationSource Format="MATHML"><math> <msup> <mrow> <mi mathvariant="double-struck">H</mi> </mrow> <mi>d</mi> </msup> </math></EquationSource> </InlineEquation> for diagonal and Hermitian matrices <i>T</i> are given. Further, these characterization for the infinite dimensional case where the operator is assumed to be diagonalizable are proved. Furthermore, we prove that for the case of a finite index set <InlineEquation ID="IEq8"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="40863_2025_496_Article_IEq3.gif" Format="GIF" Height="15" Rendition="HTML" Resolution="72" Type="Linedraw" Width="17" /> </InlineMediaObject> <EquationSource Format="TEX">\(\mathcal {J}\)</EquationSource> <EquationSource Format="MATHML"><math> <mi mathvariant="script">J</mi> </math></EquationSource> </InlineEquation>, the system <InlineEquation ID="IEq9"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="40863_2025_496_Article_IEq6.gif" Format="GIF" Height="14" Rendition="HTML" Resolution="72" Type="Linedraw" Width="14" /> </InlineMediaObject> <EquationSource Format="TEX">\(\mathcal {T}\)</EquationSource> <EquationSource Format="MATHML"><math> <mi mathvariant="script">T</mi> </math></EquationSource> </InlineEquation> never forms a minimal set and hence a basis for a right-quaternionic Hilbert space <InlineEquation ID="IEq10"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="40863_2025_496_Article_IEq10.gif" Format="GIF" Height="14" Rendition="HTML" Resolution="72" Type="Linedraw" Width="19" /> </InlineMediaObject> <EquationSource Format="TEX">\(\mathcal {H}\)</EquationSource> <EquationSource Format="MATHML"><math> <mi mathvariant="script">H</mi> </math></EquationSource> </InlineEquation>. Also, some specific conditions under which <InlineEquation ID="IEq11"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="40863_2025_496_Article_IEq6.gif" Format="GIF" Height="14" Rendition="HTML" Resolution="72" Type="Linedraw" Width="14" /> </InlineMediaObject> <EquationSource Format="TEX">\(\mathcal {T}\)</EquationSource> <EquationSource Format="MATHML"><math> <mi mathvariant="script">T</mi> </math></EquationSource> </InlineEquation> forms a frame for <InlineEquation ID="IEq12"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="40863_2025_496_Article_IEq10.gif" Format="GIF" Height="14" Rendition="HTML" Resolution="72" Type="Linedraw" Width="19" /> </InlineMediaObject> <EquationSource Format="TEX">\(\mathcal {H}\)</EquationSource> <EquationSource Format="MATHML"><math> <mi mathvariant="script">H</mi> </math></EquationSource> </InlineEquation> with finite set <i>J</i> are discussed. Finally, some characterizations for the system <InlineEquation ID="IEq13"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="40863_2025_496_Article_IEq6.gif" Format="GIF" Height="14" Rendition="HTML" Resolution="72" Type="Linedraw" Width="14" /> </InlineMediaObject> <EquationSource Format="TEX">\(\mathcal {T}\)</EquationSource> <EquationSource Format="MATHML"><math> <mi mathvariant="script">T</mi> </math></EquationSource> </InlineEquation> to form a frame for <InlineEquation ID="IEq14"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="40863_2025_496_Article_IEq10.gif" Format="GIF" Height="14" Rendition="HTML" Resolution="72" Type="Linedraw" Width="19" /> </InlineMediaObject> <EquationSource Format="TEX">\(\mathcal {H}\)</EquationSource> <EquationSource Format="MATHML"><math> <mi mathvariant="script">H</mi> </math></EquationSource> </InlineEquation> for general bounded operators in terms of strongly stable contractions are given.</p>

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Dynamical sampling in quaternionic Hilbert spaces

  • Ruchi Bhardwaj,
  • Raksha Sharma,
  • S. K. Sharma

摘要

In this article, our main goal is to extend the concept of dynamical sampling to quaternionic Hilbert spaces. The problem is to recover the initial state of an evolving function \(\mathfrak {f}\) f from the system \(\mathcal {T}:=\{T^{n}\mathfrak {f}(m):n\in \Omega _m\text {, }m\in \mathcal {J}\}\) T : = { T n f ( m ) : n Ω m , m J } of its spatial sampling taken at different time levels n, where \(\mathcal {J}\) J is an index set and \(\Omega _m=\{0\text {, }1\text {,}\dots \text {, }k_m\}\) Ω m = { 0 , 1 , , k m } . Initially the finite dimensional case for \(\mathbb {H}^d\) H d is studied and some characterizations for the system \(\mathcal {T}\) T to form a frame for \(\mathbb {H}^d\) H d for diagonal and Hermitian matrices T are given. Further, these characterization for the infinite dimensional case where the operator is assumed to be diagonalizable are proved. Furthermore, we prove that for the case of a finite index set \(\mathcal {J}\) J , the system \(\mathcal {T}\) T never forms a minimal set and hence a basis for a right-quaternionic Hilbert space \(\mathcal {H}\) H . Also, some specific conditions under which \(\mathcal {T}\) T forms a frame for \(\mathcal {H}\) H with finite set J are discussed. Finally, some characterizations for the system \(\mathcal {T}\) T to form a frame for \(\mathcal {H}\) H for general bounded operators in terms of strongly stable contractions are given.