<p>In this paper, the author proves that if the dual <i>X</i>* of <i>X</i> is weakly locally uniformly convex and the convex function <i>f</i> is continuous on <i>X</i>, then there exist two sequences <InlineEquation ID="IEq1"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="11401_2025_15_Article_IEq1.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="58" /> </InlineMediaObject> <EquationSource Format="TEX">\(\{f_{n}\}_{n=1}^{\infty}\)</EquationSource> <EquationSource Format="MATHML"><math display="block"> <mo fence="false" stretchy="false">{</mo> <msub> <mi>f</mi> <mrow> <mi>n</mi> </mrow> </msub> <msubsup> <mo fence="false" stretchy="false">}</mo> <mrow> <mi>n</mi> <mo>=</mo> <mn>1</mn> </mrow> <mrow> <mi mathvariant="normal">∞</mi> </mrow> </msubsup> </math></EquationSource> </InlineEquation> and <InlineEquation ID="IEq2"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="11401_2025_15_Article_IEq2.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="57" /> </InlineMediaObject> <EquationSource Format="TEX">\(\{g_{n}\}_{n=1}^{\infty}\)</EquationSource> <EquationSource Format="MATHML"><math display="block"> <mo fence="false" stretchy="false">{</mo> <msub> <mi>g</mi> <mrow> <mi>n</mi> </mrow> </msub> <msubsup> <mo fence="false" stretchy="false">}</mo> <mrow> <mi>n</mi> <mo>=</mo> <mn>1</mn> </mrow> <mrow> <mi mathvariant="normal">∞</mi> </mrow> </msubsup> </math></EquationSource> </InlineEquation> of continuous functions on <i>X</i>** such that (1) <i>f</i><sub><i>n</i></sub>(<i>x</i>) ≤ <i>f</i><sub><i>n</i>+1</sub>(<i>x</i>) ≤ <i>f</i>(<i>x</i>) ≤ <i>g</i><sub><i>n</i>+1</sub>(<i>x</i>) ≤ <i>g</i><sub><i>n</i></sub>(<i>x</i>) whenever <i>x</i> ∈ <i>X</i>; (2) the two convex functions <i>f</i><sub><i>n</i></sub> and <i>g</i><sub><i>n</i></sub> are Gâteaux differentiable on <i>X</i>; (3) <i>f</i><sub><i>n</i></sub> → <i>f</i> and <i>g</i><sub><i>n</i></sub> → <i>f</i> uniformly on <i>X</i>. Moreover, if the function <i>f</i> is coercive on <i>X</i>, then (1) <i>f</i><sub><i>n</i></sub> and <i>g</i><sub><i>n</i></sub> are two <i>w</i>*-lower semicontinuous convex functions on <i>X</i>*; (2) <InlineEquation ID="IEq3"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="11401_2025_15_Article_IEq3.gif" Format="GIF" Height="27" Rendition="HTML" Resolution="72" Type="Linedraw" Width="202" /> </InlineMediaObject> <EquationSource Format="TEX">\(\text{epi}\;f_{n}=\overline{\text{epi}\;f_{n}\cap(X\times R)}^{w^{\ast}}\)</EquationSource> <EquationSource Format="MATHML"><math display="block"> <mtext>epi</mtext> <mspace width="thickmathspace" /> <msub> <mi>f</mi> <mrow> <mi>n</mi> </mrow> </msub> <mo>=</mo> <msup> <mover> <mrow> <mtext>epi</mtext> <mspace width="thickmathspace" /> <msub> <mi>f</mi> <mrow> <mi>n</mi> </mrow> </msub> <mo>∩</mo> <mo stretchy="false">(</mo> <mi>X</mi> <mo>×</mo> <mi>R</mi> <mo stretchy="false">)</mo> </mrow> <mo accent="false">¯</mo> </mover> <mrow> <msup> <mi>w</mi> <mrow> <mo>∗</mo> </mrow> </msup> </mrow> </msup> </math></EquationSource> </InlineEquation> and <InlineEquation ID="IEq4"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="11401_2025_15_Article_IEq4.gif" Format="GIF" Height="27" Rendition="HTML" Resolution="72" Type="Linedraw" Width="201" /> </InlineMediaObject> <EquationSource Format="TEX">\(\text{epi}\;g_{n}=\overline{\text{epi}\;g_{n}\cap(X\times R)}^{w^{\ast}}\)</EquationSource> <EquationSource Format="MATHML"><math display="block"> <mtext>epi</mtext> <mspace width="thickmathspace" /> <msub> <mi>g</mi> <mrow> <mi>n</mi> </mrow> </msub> <mo>=</mo> <msup> <mover> <mrow> <mtext>epi</mtext> <mspace width="thickmathspace" /> <msub> <mi>g</mi> <mrow> <mi>n</mi> </mrow> </msub> <mo>∩</mo> <mo stretchy="false">(</mo> <mi>X</mi> <mo>×</mo> <mi>R</mi> <mo stretchy="false">)</mo> </mrow> <mo accent="false">¯</mo> </mover> <mrow> <msup> <mi>w</mi> <mrow> <mo>∗</mo> </mrow> </msup> </mrow> </msup> </math></EquationSource> </InlineEquation>.</p>

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Convexity and Uniform Monotone Approximation of Differentiable Function in Banach Spaces

  • Shaoqiang Shang

摘要

In this paper, the author proves that if the dual X* of X is weakly locally uniformly convex and the convex function f is continuous on X, then there exist two sequences \(\{f_{n}\}_{n=1}^{\infty}\) { f n } n = 1 and \(\{g_{n}\}_{n=1}^{\infty}\) { g n } n = 1 of continuous functions on X** such that (1) fn(x) ≤ fn+1(x) ≤ f(x) ≤ gn+1(x) ≤ gn(x) whenever xX; (2) the two convex functions fn and gn are Gâteaux differentiable on X; (3) fnf and gnf uniformly on X. Moreover, if the function f is coercive on X, then (1) fn and gn are two w*-lower semicontinuous convex functions on X*; (2) \(\text{epi}\;f_{n}=\overline{\text{epi}\;f_{n}\cap(X\times R)}^{w^{\ast}}\) epi f n = epi f n ( X × R ) ¯ w and \(\text{epi}\;g_{n}=\overline{\text{epi}\;g_{n}\cap(X\times R)}^{w^{\ast}}\) epi g n = epi g n ( X × R ) ¯ w .