<p>We consider Hermitian Toeplitz matrices <InlineEquation ID="IEq1"> <EquationSource Format="TEX">\(T_{n}(A_{n})\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi>T</mi> <mi>n</mi> </msub> <mrow> <mo stretchy="false">(</mo> <msub> <mi>A</mi> <mi>n</mi> </msub> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation> generated by symbols&#xa0;<InlineEquation ID="IEq2"> <EquationSource Format="TEX">\(A_{n}\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>A</mi> <mi>n</mi> </msub> </math></EquationSource> </InlineEquation> that depend on the matrix size <InlineEquation ID="IEq3"> <EquationSource Format="TEX">\(n\)</EquationSource> <EquationSource Format="MATHML"><math> <mi>n</mi> </math></EquationSource> </InlineEquation>. These symbols take the form <Equation ID="Equ18"> <EquationSource Format="TEX">\( A_{n}(\theta )=a_{0}(\theta )+\sum _{k=1}^{\infty }\beta _{n,k}\,a_{k}(\theta ), \)</EquationSource> <EquationSource Format="MATHML"><math display="block"> <mrow> <msub> <mi>A</mi> <mi>n</mi> </msub> <mrow> <mo stretchy="false">(</mo> <mi>θ</mi> <mo stretchy="false">)</mo> </mrow> <mo>=</mo> <msub> <mi>a</mi> <mn>0</mn> </msub> <mrow> <mo stretchy="false">(</mo> <mi>θ</mi> <mo stretchy="false">)</mo> </mrow> <mo>+</mo> <munderover> <mo>∑</mo> <mrow> <mi>k</mi> <mo>=</mo> <mn>1</mn> </mrow> <mi>∞</mi> </munderover> <msub> <mi>β</mi> <mrow> <mi>n</mi> <mo>,</mo> <mi>k</mi> </mrow> </msub> <mspace width="0.166667em" /> <msub> <mi>a</mi> <mi>k</mi> </msub> <mrow> <mo stretchy="false">(</mo> <mi>θ</mi> <mo stretchy="false">)</mo> </mrow> <mo>,</mo> </mrow> </math></EquationSource> </Equation>where&#xa0;<InlineEquation ID="IEq4"> <EquationSource Format="TEX">\(A_{n}\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>A</mi> <mi>n</mi> </msub> </math></EquationSource> </InlineEquation> and <InlineEquation ID="IEq5"> <EquationSource Format="TEX">\(a_{0}\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>a</mi> <mn>0</mn> </msub> </math></EquationSource> </InlineEquation> belong to the simple-loop class <InlineEquation ID="IEq6"> <EquationSource Format="TEX">\({{\,\textrm{SL}\,}}^{\alpha }\)</EquationSource> <EquationSource Format="MATHML"><math> <msup> <mrow> <mrow> <mspace width="0.166667em" /> <mtext>SL</mtext> <mspace width="0.166667em" /> </mrow> </mrow> <mi>α</mi> </msup> </math></EquationSource> </InlineEquation> for some <InlineEquation ID="IEq7"> <EquationSource Format="TEX">\(\alpha \geqslant 2\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>α</mi> <mo>⩾</mo> <mn>2</mn> </mrow> </math></EquationSource> </InlineEquation>. Under suitable assumptions on the decay of the coefficients <InlineEquation ID="IEq8"> <EquationSource Format="TEX">\(\beta _{n,k}\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>β</mi> <mrow> <mi>n</mi> <mo>,</mo> <mi>k</mi> </mrow> </msub> </math></EquationSource> </InlineEquation> and the regularity of the functions&#xa0;<InlineEquation ID="IEq9"> <EquationSource Format="TEX">\(a_{k}\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>a</mi> <mi>k</mi> </msub> </math></EquationSource> </InlineEquation>, we prove that the eigenvalues of <InlineEquation ID="IEq10"> <EquationSource Format="TEX">\(T_{n}(A_{n})\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi>T</mi> <mi>n</mi> </msub> <mrow> <mo stretchy="false">(</mo> <msub> <mi>A</mi> <mi>n</mi> </msub> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation> admit a full asymptotic expansion uniformly in the bulk of the spectrum. This work generalizes previous results for fixed and finitely perturbed simple-loop symbols.</p>

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EIGENVALUE SUPERPOSITION FOR SERIES OF TOEPLITZ MATRICES WITH MATRIX-SIZE DEPENDENT GENERATING FUNCTIONS

  • M. Bogoya,
  • S. Serra-Capizzano

摘要

We consider Hermitian Toeplitz matrices \(T_{n}(A_{n})\) T n ( A n ) generated by symbols  \(A_{n}\) A n that depend on the matrix size \(n\) n . These symbols take the form \( A_{n}(\theta )=a_{0}(\theta )+\sum _{k=1}^{\infty }\beta _{n,k}\,a_{k}(\theta ), \) A n ( θ ) = a 0 ( θ ) + k = 1 β n , k a k ( θ ) , where  \(A_{n}\) A n and \(a_{0}\) a 0 belong to the simple-loop class \({{\,\textrm{SL}\,}}^{\alpha }\) SL α for some \(\alpha \geqslant 2\) α 2 . Under suitable assumptions on the decay of the coefficients \(\beta _{n,k}\) β n , k and the regularity of the functions  \(a_{k}\) a k , we prove that the eigenvalues of \(T_{n}(A_{n})\) T n ( A n ) admit a full asymptotic expansion uniformly in the bulk of the spectrum. This work generalizes previous results for fixed and finitely perturbed simple-loop symbols.