<p>Assume that <InlineEquation ID="IEq1"> <EquationSource Format="TEX">\((\Omega ,\mathcal A,\mathbb {P})\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mo stretchy="false">(</mo> <mi mathvariant="normal">Ω</mi> <mo>,</mo> <mi mathvariant="script">A</mi> <mo>,</mo> <mi mathvariant="double-struck">P</mi> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation> is a probability space, <InlineEquation ID="IEq2"> <EquationSource Format="TEX">\((X,\rho )\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mo stretchy="false">(</mo> <mi>X</mi> <mo>,</mo> <mi>ρ</mi> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation> is a compact metric space and <i>Y</i> is a separable Banach space. Under relevant assumptions about the given function <InlineEquation ID="IEq3"> <EquationSource Format="TEX">\( f :X \times \Omega \rightarrow X \)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>f</mi> <mo>:</mo> <mi>X</mi> <mo>×</mo> <mi mathvariant="normal">Ω</mi> <mo stretchy="false">→</mo> <mi>X</mi> </mrow> </math></EquationSource> </InlineEquation> we show that the set of all continuous functions <InlineEquation ID="IEq4"> <EquationSource Format="TEX">\(F :X \rightarrow Y\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>F</mi> <mo>:</mo> <mi>X</mi> <mo stretchy="false">→</mo> <mi>Y</mi> </mrow> </math></EquationSource> </InlineEquation> such that the equation <Equation ID="Equ14"> <EquationSource Format="TEX">\(\begin{aligned} \varphi (x)=\int _{\Omega }\varphi \big (f(x,\omega )\big )\mathbb {P}(d\omega )+F(x) \end{aligned}\)</EquationSource> <EquationSource Format="MATHML"><math display="block"> <mrow> <mtable> <mtr> <mtd columnalign="right"> <mrow> <mi>φ</mi> <mrow> <mo stretchy="false">(</mo> <mi>x</mi> <mo stretchy="false">)</mo> </mrow> <mo>=</mo> <msub> <mo>∫</mo> <mi mathvariant="normal">Ω</mi> </msub> <mi>φ</mi> <mrow> <mo maxsize="1.2em" minsize="1.2em" stretchy="true">(</mo> </mrow> <mi>f</mi> <mrow> <mo stretchy="false">(</mo> <mi>x</mi> <mo>,</mo> <mi>ω</mi> <mo stretchy="false">)</mo> </mrow> <mrow> <mo maxsize="1.2em" minsize="1.2em" stretchy="true">)</mo> </mrow> <mi mathvariant="double-struck">P</mi> <mrow> <mo stretchy="false">(</mo> <mi>d</mi> <mi>ω</mi> <mo stretchy="false">)</mo> </mrow> <mo>+</mo> <mi>F</mi> <mrow> <mo stretchy="false">(</mo> <mi>x</mi> <mo stretchy="false">)</mo> </mrow> </mrow> </mtd> </mtr> </mtable> </mrow> </math></EquationSource> </Equation>has a continuous solution <InlineEquation ID="IEq5"> <EquationSource Format="TEX">\(\varphi :X \rightarrow Y\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>φ</mi> <mo>:</mo> <mi>X</mi> <mo stretchy="false">→</mo> <mi>Y</mi> </mrow> </math></EquationSource> </InlineEquation> is small from the points of view of both category and measure theory.</p>

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On some linear functional equations with continuous solutions

  • Karol Baron

摘要

Assume that \((\Omega ,\mathcal A,\mathbb {P})\) ( Ω , A , P ) is a probability space, \((X,\rho )\) ( X , ρ ) is a compact metric space and Y is a separable Banach space. Under relevant assumptions about the given function \( f :X \times \Omega \rightarrow X \) f : X × Ω X we show that the set of all continuous functions \(F :X \rightarrow Y\) F : X Y such that the equation \(\begin{aligned} \varphi (x)=\int _{\Omega }\varphi \big (f(x,\omega )\big )\mathbb {P}(d\omega )+F(x) \end{aligned}\) φ ( x ) = Ω φ ( f ( x , ω ) ) P ( d ω ) + F ( x ) has a continuous solution \(\varphi :X \rightarrow Y\) φ : X Y is small from the points of view of both category and measure theory.