<p>We consider a normalized indeterminate Hamburger moment sequence <i>s</i> which is supposed to be Stieltjes. We revisit old results of Chihara, Berg-Valent and Henrik L. Pedersen about determinacy/indeterminacy in the sense of Stieltjes for <i>s</i> and related to a constant <InlineEquation ID="IEq1"> <EquationSource Format="TEX">\(\alpha (s)\le 0,\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>α</mi> <mo stretchy="false">(</mo> <mi>s</mi> <mo stretchy="false">)</mo> <mo>≤</mo> <mn>0</mn> <mo>,</mo> </mrow> </math></EquationSource> </InlineEquation> which can be defined using the corresponding orthogonal polynomials and those of the second kind. We recall how <InlineEquation ID="IEq2"> <EquationSource Format="TEX">\(\alpha (s)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>α</mi> <mo stretchy="false">(</mo> <mi>s</mi> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation> can be defined in terms of the entire functions <i>B</i> and <i>D</i> from the Nevanlinna matrix, and we find a similar expression involving the functions <i>A</i> and <i>C</i>. The constant <InlineEquation ID="IEq3"> <EquationSource Format="TEX">\(\alpha (s)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>α</mi> <mo stretchy="false">(</mo> <mi>s</mi> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation> determines the Friedrichs extension of the Jacobi matrix when used as parameter in the Nevanlinna parametrization of the indeterminate moment problem. We prove how the zeros of the corresponding orthogonal polynomials converge to the mass-points of the Friedrichs solution of the moment problem. The graph of the function <InlineEquation ID="IEq4"> <EquationSource Format="TEX">\(j(x)=D(x)/B(x)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>j</mi> <mo stretchy="false">(</mo> <mi>x</mi> <mo stretchy="false">)</mo> <mo>=</mo> <mi>D</mi> <mo stretchy="false">(</mo> <mi>x</mi> <mo stretchy="false">)</mo> <mo stretchy="false">/</mo> <mi>B</mi> <mo stretchy="false">(</mo> <mi>x</mi> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation> shows that the supports of the N-extremal solutions are bounded below and the lower bound can be any number in the interval <InlineEquation ID="IEq5"> <EquationSource Format="TEX">\((-\infty ,\xi _1],\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mo stretchy="false">(</mo> <mo>-</mo> <mi>∞</mi> <mo>,</mo> <msub> <mi>ξ</mi> <mn>1</mn> </msub> <mo stretchy="false">]</mo> <mo>,</mo> </mrow> </math></EquationSource> </InlineEquation> where <InlineEquation ID="IEq6"> <EquationSource Format="TEX">\(\xi _1\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>ξ</mi> <mn>1</mn> </msub> </math></EquationSource> </InlineEquation> is the lower bound of the Friedrichs measure.</p>

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Indeterminate Stieltjes moment problems revisited

  • Christian Berg

摘要

We consider a normalized indeterminate Hamburger moment sequence s which is supposed to be Stieltjes. We revisit old results of Chihara, Berg-Valent and Henrik L. Pedersen about determinacy/indeterminacy in the sense of Stieltjes for s and related to a constant \(\alpha (s)\le 0,\) α ( s ) 0 , which can be defined using the corresponding orthogonal polynomials and those of the second kind. We recall how \(\alpha (s)\) α ( s ) can be defined in terms of the entire functions B and D from the Nevanlinna matrix, and we find a similar expression involving the functions A and C. The constant \(\alpha (s)\) α ( s ) determines the Friedrichs extension of the Jacobi matrix when used as parameter in the Nevanlinna parametrization of the indeterminate moment problem. We prove how the zeros of the corresponding orthogonal polynomials converge to the mass-points of the Friedrichs solution of the moment problem. The graph of the function \(j(x)=D(x)/B(x)\) j ( x ) = D ( x ) / B ( x ) shows that the supports of the N-extremal solutions are bounded below and the lower bound can be any number in the interval \((-\infty ,\xi _1],\) ( - , ξ 1 ] , where \(\xi _1\) ξ 1 is the lower bound of the Friedrichs measure.