<p>This paper presents an investigation of the asymptotic behavior within natural exponential families, with particular focus on the limiting distributions of scaled family. We examine the scaled random variable <InlineEquation ID="IEq1"> <EquationSource Format="TEX">\(Y_t = \frac{X_t}{t}\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi>Y</mi> <mi>t</mi> </msub> <mo>=</mo> <mfrac> <msub> <mi>X</mi> <mi>t</mi> </msub> <mi>t</mi> </mfrac> </mrow> </math></EquationSource> </InlineEquation>, where <InlineEquation ID="IEq2"> <EquationSource Format="TEX">\(X_t\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>X</mi> <mi>t</mi> </msub> </math></EquationSource> </InlineEquation> belongs to a natural exponential family with mean parameter <i>tm</i> (<InlineEquation ID="IEq3"> <EquationSource Format="TEX">\(m &gt; 0\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>m</mi> <mo>&gt;</mo> <mn>0</mn> </mrow> </math></EquationSource> </InlineEquation>) as <InlineEquation ID="IEq4"> <EquationSource Format="TEX">\(t \rightarrow 0^+\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>t</mi> <mo stretchy="false">→</mo> <msup> <mn>0</mn> <mo>+</mo> </msup> </mrow> </math></EquationSource> </InlineEquation>. Under the fundamental assumption that the second derivative of the variance function <i>V</i> extends continuously to zero with <InlineEquation ID="IEq5"> <EquationSource Format="TEX">\(V''(0) \ne 0\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msup> <mi>V</mi> <mrow> <mo>′</mo> <mo>′</mo> </mrow> </msup> <mrow> <mo stretchy="false">(</mo> <mn>0</mn> <mo stretchy="false">)</mo> </mrow> <mo>≠</mo> <mn>0</mn> </mrow> </math></EquationSource> </InlineEquation>, we establish that <InlineEquation ID="IEq6"> <EquationSource Format="TEX">\(Y_t\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>Y</mi> <mi>t</mi> </msub> </math></EquationSource> </InlineEquation> converges in distribution to a Gamma law with explicitly determined shape and rate parameters <InlineEquation ID="IEq7"> <EquationSource Format="TEX">\(\alpha = \frac{2}{V''(0)}\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>α</mi> <mo>=</mo> <mfrac> <mn>2</mn> <mrow> <msup> <mi>V</mi> <mrow> <mo>′</mo> <mo>′</mo> </mrow> </msup> <mrow> <mo stretchy="false">(</mo> <mn>0</mn> <mo stretchy="false">)</mo> </mrow> </mrow> </mfrac> </mrow> </math></EquationSource> </InlineEquation> and <InlineEquation ID="IEq8"> <EquationSource Format="TEX">\(\beta = \frac{2}{m V''(0)}\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>β</mi> <mo>=</mo> <mfrac> <mn>2</mn> <mrow> <mi>m</mi> <msup> <mi>V</mi> <mrow> <mo>′</mo> <mo>′</mo> </mrow> </msup> <mrow> <mo stretchy="false">(</mo> <mn>0</mn> <mo stretchy="false">)</mo> </mrow> </mrow> </mfrac> </mrow> </math></EquationSource> </InlineEquation>, respectively. The proposed proof integrates tools from convex analysis, probability theory, and functional analysis, including the Arzelà-Ascoli theorem. The paper also provides a detailed illustrative example using the uniform distribution on [0,&#xa0;1], where the limiting distribution simplifies to an exponential law.</p>

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Limit Laws for Scaled Natural Exponential Families: A Gamma Convergence Result

  • Khalil Masmoudi

摘要

This paper presents an investigation of the asymptotic behavior within natural exponential families, with particular focus on the limiting distributions of scaled family. We examine the scaled random variable \(Y_t = \frac{X_t}{t}\) Y t = X t t , where \(X_t\) X t belongs to a natural exponential family with mean parameter tm ( \(m > 0\) m > 0 ) as \(t \rightarrow 0^+\) t 0 + . Under the fundamental assumption that the second derivative of the variance function V extends continuously to zero with \(V''(0) \ne 0\) V ( 0 ) 0 , we establish that \(Y_t\) Y t converges in distribution to a Gamma law with explicitly determined shape and rate parameters \(\alpha = \frac{2}{V''(0)}\) α = 2 V ( 0 ) and \(\beta = \frac{2}{m V''(0)}\) β = 2 m V ( 0 ) , respectively. The proposed proof integrates tools from convex analysis, probability theory, and functional analysis, including the Arzelà-Ascoli theorem. The paper also provides a detailed illustrative example using the uniform distribution on [0, 1], where the limiting distribution simplifies to an exponential law.