<p>A functional Hilbert space is the Hilbert space of complex-valued functions on some set <InlineEquation ID="IEq1"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="13660_2025_3255_Article_IEq1.gif" Format="GIF" Height="16" Rendition="HTML" Resolution="72" Type="Linedraw" Width="49" /> </InlineMediaObject> <EquationSource Format="MATHML"><math> <mi mathvariant="normal">Θ</mi> <mo>⊆</mo> <mi mathvariant="script">C</mi> </math></EquationSource> <EquationSource Format="TEX">$\Theta \subseteq \mathcal {C}$</EquationSource> </InlineEquation> that the evaluation functionals <InlineEquation ID="IEq2"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="13660_2025_3255_Article_IEq2.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="103" /> </InlineMediaObject> <EquationSource Format="MATHML"><math> <msub> <mi>φ</mi> <mi>λ</mi> </msub> <mrow> <mo>(</mo> <mi>f</mi> <mo>)</mo> </mrow> <mo>=</mo> <mi>f</mi> <mrow> <mo>(</mo> <mi>λ</mi> <mo>)</mo> </mrow> </math></EquationSource> <EquationSource Format="TEX">$\varphi _{\lambda}\left ( f\right ) =f\left ( \lambda \right ) $</EquationSource> </InlineEquation>, <InlineEquation ID="IEq3"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="13660_2025_3255_Article_IEq3.gif" Format="GIF" Height="15" Rendition="HTML" Resolution="72" Type="Linedraw" Width="45" /> </InlineMediaObject> <EquationSource Format="MATHML"><math> <mi>λ</mi> <mo>∈</mo> <mi mathvariant="normal">Θ</mi> </math></EquationSource> <EquationSource Format="TEX">$\lambda \in \Theta $</EquationSource> </InlineEquation> are continuous on <InlineEquation ID="IEq4"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="13660_2025_3255_Article_IEq4.gif" Format="GIF" Height="14" Rendition="HTML" Resolution="72" Type="Linedraw" Width="19" /> </InlineMediaObject> <EquationSource Format="MATHML"><math> <mi mathvariant="script">H</mi> </math></EquationSource> <EquationSource Format="TEX">$\mathcal {H}$</EquationSource> </InlineEquation>. Then, by the Riesz representation theorem, there is a unique element <InlineEquation ID="IEq5"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="13660_2025_3255_Article_IEq5.gif" Format="GIF" Height="16" Rendition="HTML" Resolution="72" Type="Linedraw" Width="56" /> </InlineMediaObject> <EquationSource Format="MATHML"><math> <msub> <mi>k</mi> <mi>λ</mi> </msub> <mo>∈</mo> <mi mathvariant="script">H</mi> </math></EquationSource> <EquationSource Format="TEX">$k_{\lambda}\in \mathcal {H}$</EquationSource> </InlineEquation> such that <InlineEquation ID="IEq6"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="13660_2025_3255_Article_IEq6.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="109" /> </InlineMediaObject> <EquationSource Format="MATHML"><math> <mi>f</mi> <mrow> <mo>(</mo> <mi>λ</mi> <mo>)</mo> </mrow> <mo>=</mo> <mrow> <mo>〈</mo> <mi>f</mi> <mo>,</mo> <msub> <mi>k</mi> <mi>λ</mi> </msub> <mo>〉</mo> </mrow> </math></EquationSource> <EquationSource Format="TEX">$f\left ( \lambda \right ) =\left \langle f,k_{\lambda}\right \rangle $</EquationSource> </InlineEquation> for all <InlineEquation ID="IEq7"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="13660_2025_3255_Article_IEq7.gif" Format="GIF" Height="17" Rendition="HTML" Resolution="72" Type="Linedraw" Width="51" /> </InlineMediaObject> <EquationSource Format="MATHML"><math> <mi>f</mi> <mo>∈</mo> <mi mathvariant="script">H</mi> </math></EquationSource> <EquationSource Format="TEX">$f\in \mathcal {H}$</EquationSource> </InlineEquation> and every <InlineEquation ID="IEq8"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="13660_2025_3255_Article_IEq8.gif" Format="GIF" Height="15" Rendition="HTML" Resolution="72" Type="Linedraw" Width="45" /> </InlineMediaObject> <EquationSource Format="MATHML"><math> <mi>λ</mi> <mo>∈</mo> <mi mathvariant="normal">Θ</mi> </math></EquationSource> <EquationSource Format="TEX">$\lambda \in \Theta $</EquationSource> </InlineEquation>. The function <i>k</i> on <InlineEquation ID="IEq9"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="13660_2025_3255_Article_IEq9.gif" Format="GIF" Height="15" Rendition="HTML" Resolution="72" Type="Linedraw" Width="48" /> </InlineMediaObject> <EquationSource Format="MATHML"><math> <mi mathvariant="normal">Θ</mi> <mo>×</mo> <mi mathvariant="normal">Θ</mi> </math></EquationSource> <EquationSource Format="TEX">$\Theta \times \Theta $</EquationSource> </InlineEquation> defined by <InlineEquation ID="IEq10"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="13660_2025_3255_Article_IEq10.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="114" /> </InlineMediaObject> <EquationSource Format="MATHML"><math> <mi>k</mi> <mrow> <mo>(</mo> <mi>z</mi> <mo>,</mo> <mi>λ</mi> <mo>)</mo> </mrow> <mo>=</mo> <msub> <mi>k</mi> <mi>λ</mi> </msub> <mrow> <mo>(</mo> <mi>z</mi> <mo>)</mo> </mrow> </math></EquationSource> <EquationSource Format="TEX">$k\left ( z,\lambda \right ) =k_{\lambda}\left ( z\right ) $</EquationSource> </InlineEquation> is called the reproducing kernel of <InlineEquation ID="IEq11"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="13660_2025_3255_Article_IEq11.gif" Format="GIF" Height="14" Rendition="HTML" Resolution="72" Type="Linedraw" Width="19" /> </InlineMediaObject> <EquationSource Format="MATHML"><math> <mi mathvariant="script">H</mi> </math></EquationSource> <EquationSource Format="TEX">$\mathcal {H}$</EquationSource> </InlineEquation>. In this study, we defined the weighted Davis-Wielandt Berezin number, and then we obtained some related inequalities. It is shown, among other inequalities, that if <InlineEquation ID="IEq12"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="13660_2025_3255_Article_IEq12.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="77" /> </InlineMediaObject> <EquationSource Format="MATHML"><math> <mi>X</mi> <mo>∈</mo> <mi mathvariant="script">L</mi> <mo stretchy="false">(</mo> <mi mathvariant="script">H</mi> <mo stretchy="false">)</mo> </math></EquationSource> <EquationSource Format="TEX">$X\in{\mathcal {L}}({\mathcal {H}})$</EquationSource> </InlineEquation> and <InlineEquation ID="IEq13"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="13660_2025_3255_Article_IEq13.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="64" /> </InlineMediaObject> <EquationSource Format="MATHML"><math> <mi>ν</mi> <mo>∈</mo> <mo stretchy="false">[</mo> <mn>0</mn> <mo>,</mo> <mn>1</mn> <mo stretchy="false">]</mo> </math></EquationSource> <EquationSource Format="TEX">$\nu \in [0,1]$</EquationSource> </InlineEquation>, then <Equation ID="Equa"> <MediaObject> <ImageObject Color="BlackWhite" FileRef="13660_2025_3255_Article_Equa.gif" Format="GIF" Height="101" Rendition="HTML" Resolution="72" Type="Linedraw" Width="472" /> </MediaObject> <EquationSource Format="MATHML"><math> <mtable columnalign="right left" columnspacing="0.2em"> <mtr> <mtd> <mfrac> <mrow> <mn>1</mn> </mrow> <mn>2</mn> </mfrac> <mo maxsize="3.8ex" minsize="3.8ex" stretchy="true">(</mo> <msup> <mtext mathvariant="bold">ber</mtext> <mn>2</mn> </msup> <mo stretchy="false">(</mo> <msub> <mi>X</mi> <mi>ν</mi> </msub> <mo>+</mo> <mo stretchy="false">|</mo> <msub> <mi>X</mi> <mi>ν</mi> </msub> <msup> <mo stretchy="false">|</mo> <mn>2</mn> </msup> <mo stretchy="false">)</mo> </mtd> <mtd> <mo>+</mo> <msubsup> <mi>c</mi> <mtext mathvariant="bold">ber</mtext> <mn>2</mn> </msubsup> <mo stretchy="false">(</mo> <msub> <mi>X</mi> <mi>ν</mi> </msub> <mo>−</mo> <mo stretchy="false">|</mo> <msub> <mi>X</mi> <mi>ν</mi> </msub> <msup> <mo stretchy="false">|</mo> <mn>2</mn> </msup> <mo stretchy="false">)</mo> <mo maxsize="3.8ex" minsize="3.8ex" stretchy="true">)</mo> </mtd> </mtr> <mtr> <mtd /> <mtd> <mo>≤</mo> <mi>d</mi> <msubsup> <mi>w</mi> <msub> <mtext mathvariant="bold">ber</mtext> <mi>ν</mi> </msub> <mn>2</mn> </msubsup> <mo stretchy="false">(</mo> <mi>X</mi> <mo stretchy="false">)</mo> </mtd> </mtr> <mtr> <mtd /> <mtd> <mo>≤</mo> <mfrac> <mrow> <mn>1</mn> </mrow> <mn>2</mn> </mfrac> <mrow> <mo>(</mo> <msup> <mtext mathvariant="bold">ber</mtext> <mn>2</mn> </msup> <mo stretchy="false">(</mo> <msub> <mi>X</mi> <mi>ν</mi> </msub> <mo>+</mo> <mo stretchy="false">|</mo> <msub> <mi>X</mi> <mi>ν</mi> </msub> <msup> <mo stretchy="false">|</mo> <mn>2</mn> </msup> <mo stretchy="false">)</mo> <mo>+</mo> <msup> <mtext mathvariant="bold">ber</mtext> <mn>2</mn> </msup> <mo stretchy="false">(</mo> <msub> <mi>X</mi> <mi>ν</mi> </msub> <mo>−</mo> <mo stretchy="false">|</mo> <msub> <mi>X</mi> <mi>ν</mi> </msub> <msup> <mo stretchy="false">|</mo> <mn>2</mn> </msup> <mo stretchy="false">)</mo> <mo>)</mo> </mrow> <mo>,</mo> </mtd> </mtr> </mtable> </math></EquationSource> <EquationSource Format="TEX"> \(\begin{aligned} \frac{1}{2}\Big(\textbf{ber}^{2} (X_{\nu}+\vert X_{\nu}\vert ^{2})&amp;+c_{ \textbf{ber}}^{2}(X_{\nu}-\vert X_{\nu}\vert ^{2})\Big) \\ &amp;\leq dw_{\textbf{ber}_{\nu}}^{2}(X) \\ &amp;\leq \frac{1}{2}\left (\textbf{ber}^{2} (X_{\nu}+\vert X_{\nu}\vert ^{2})+ \textbf{ber}^{2}(X_{\nu}-\vert X_{\nu}\vert ^{2})\right ), \end{aligned}\) </EquationSource> </Equation> where <InlineEquation ID="IEq14"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="13660_2025_3255_Article_IEq14.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="162" /> </InlineMediaObject> <EquationSource Format="MATHML"><math> <msub> <mi>X</mi> <mi>ν</mi> </msub> <mo>=</mo> <mo stretchy="false">(</mo> <mn>1</mn> <mo>−</mo> <mn>2</mn> <mi>ν</mi> <mo stretchy="false">)</mo> <msup> <mi>X</mi> <mo>∗</mo> </msup> <mo>+</mo> <mi>X</mi> </math></EquationSource> <EquationSource Format="TEX">$X_{\nu}= (1-2\nu )X^{*}+X$</EquationSource> </InlineEquation>. Some bounds for the weighted Davis-Wielandt Berezin number are also established.</p>

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The weighted Davis-Wielandt Berezin number for reproducing kernel Hilbert space operators

  • Nooshin Eslami Mahdiabadi,
  • Mojtaba Bakherad,
  • Monire Hajmohamadi,
  • Mykola Petrushka

摘要

A functional Hilbert space is the Hilbert space of complex-valued functions on some set Θ C $\Theta \subseteq \mathcal {C}$ that the evaluation functionals φ λ ( f ) = f ( λ ) $\varphi _{\lambda}\left ( f\right ) =f\left ( \lambda \right ) $ , λ Θ $\lambda \in \Theta $ are continuous on H $\mathcal {H}$ . Then, by the Riesz representation theorem, there is a unique element k λ H $k_{\lambda}\in \mathcal {H}$ such that f ( λ ) = f , k λ $f\left ( \lambda \right ) =\left \langle f,k_{\lambda}\right \rangle $ for all f H $f\in \mathcal {H}$ and every λ Θ $\lambda \in \Theta $ . The function k on Θ × Θ $\Theta \times \Theta $ defined by k ( z , λ ) = k λ ( z ) $k\left ( z,\lambda \right ) =k_{\lambda}\left ( z\right ) $ is called the reproducing kernel of H $\mathcal {H}$ . In this study, we defined the weighted Davis-Wielandt Berezin number, and then we obtained some related inequalities. It is shown, among other inequalities, that if X L ( H ) $X\in{\mathcal {L}}({\mathcal {H}})$ and ν [ 0 , 1 ] $\nu \in [0,1]$ , then 1 2 ( ber 2 ( X ν + | X ν | 2 ) + c ber 2 ( X ν | X ν | 2 ) ) d w ber ν 2 ( X ) 1 2 ( ber 2 ( X ν + | X ν | 2 ) + ber 2 ( X ν | X ν | 2 ) ) , \(\begin{aligned} \frac{1}{2}\Big(\textbf{ber}^{2} (X_{\nu}+\vert X_{\nu}\vert ^{2})&+c_{ \textbf{ber}}^{2}(X_{\nu}-\vert X_{\nu}\vert ^{2})\Big) \\ &\leq dw_{\textbf{ber}_{\nu}}^{2}(X) \\ &\leq \frac{1}{2}\left (\textbf{ber}^{2} (X_{\nu}+\vert X_{\nu}\vert ^{2})+ \textbf{ber}^{2}(X_{\nu}-\vert X_{\nu}\vert ^{2})\right ), \end{aligned}\) where X ν = ( 1 2 ν ) X + X $X_{\nu}= (1-2\nu )X^{*}+X$ . Some bounds for the weighted Davis-Wielandt Berezin number are also established.