<p>Following the line of thought by P. Bouboulis &amp; S. Theodoridis, [<CitationRef CitationID="CR6">6</CitationRef>], we take up a program of recovering kernel methods (as employed in signal analysis and machine learning theory) from <i>real</i> RKHS and kernels, to the <i>complex</i> domain. We solve the maximum problem <InlineEquation ID="IEq4"> <EquationSource Format="TEX">\(\sup \, \big \{ \sum _{j=1}^p \big | f( z_j ) \big |^2 \,: \, \Vert f \Vert ^2 \le E \big \}\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mo movablelimits="true">sup</mo> <mspace width="0.166667em" /> <mrow> <mo maxsize="1.2em" minsize="1.2em" stretchy="true">{</mo> </mrow> <msubsup> <mo>∑</mo> <mrow> <mi>j</mi> <mo>=</mo> <mn>1</mn> </mrow> <mi>p</mi> </msubsup> <mrow> <mo maxsize="1.2em" minsize="1.2em" stretchy="true">|</mo> </mrow> <mi>f</mi> <mrow> <mo stretchy="false">(</mo> <msub> <mi>z</mi> <mi>j</mi> </msub> <mo stretchy="false">)</mo> </mrow> <msup> <mrow> <mo maxsize="1.2em" minsize="1.2em" stretchy="true">|</mo> </mrow> <mn>2</mn> </msup> <mspace width="0.166667em" /> <mo>:</mo> <mspace width="0.166667em" /> <msup> <mrow> <mo stretchy="false">‖</mo> <mi>f</mi> <mo stretchy="false">‖</mo> </mrow> <mn>2</mn> </msup> <mo>≤</mo> <mi>E</mi> <mrow> <mo maxsize="1.2em" minsize="1.2em" stretchy="true">}</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation> in the complex RKHS of holomorphic <InlineEquation ID="IEq5"> <EquationSource Format="TEX">\(L^2\)</EquationSource> <EquationSource Format="MATHML"><math> <msup> <mi>L</mi> <mn>2</mn> </msup> </math></EquationSource> </InlineEquation> functions <InlineEquation ID="IEq6"> <EquationSource Format="TEX">\(f: \Omega \rightarrow {\mathbb {C}}\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>f</mi> <mo>:</mo> <mi mathvariant="normal">Ω</mi> <mo stretchy="false">→</mo> <mi mathvariant="double-struck">C</mi> </mrow> </math></EquationSource> </InlineEquation>, for any bounded domain <InlineEquation ID="IEq7"> <EquationSource Format="TEX">\(\Omega \subset {\mathbb {C}}^n\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi mathvariant="normal">Ω</mi> <mo>⊂</mo> <msup> <mrow> <mi mathvariant="double-struck">C</mi> </mrow> <mi>n</mi> </msup> </mrow> </math></EquationSource> </InlineEquation> and any finite set of points <InlineEquation ID="IEq8"> <EquationSource Format="TEX">\(z_1 \,, \, \cdots \,, \, z_p \in \Omega \)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi>z</mi> <mn>1</mn> </msub> <mspace width="0.166667em" /> <mo>,</mo> <mspace width="0.166667em" /> <mo>⋯</mo> <mspace width="0.166667em" /> <mo>,</mo> <mspace width="0.166667em" /> <msub> <mi>z</mi> <mi>p</mi> </msub> <mo>∈</mo> <mi mathvariant="normal">Ω</mi> </mrow> </math></EquationSource> </InlineEquation>, and apply the result to the space <InlineEquation ID="IEq9"> <EquationSource Format="TEX">\(L^2 H({\mathbb {B}}^n )\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msup> <mi>L</mi> <mn>2</mn> </msup> <mi>H</mi> <mrow> <mo stretchy="false">(</mo> <msup> <mrow> <mi mathvariant="double-struck">B</mi> </mrow> <mi>n</mi> </msup> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation> of holomorphic <InlineEquation ID="IEq10"> <EquationSource Format="TEX">\(L^2\)</EquationSource> <EquationSource Format="MATHML"><math> <msup> <mi>L</mi> <mn>2</mn> </msup> </math></EquationSource> </InlineEquation> functions on the unit ball <InlineEquation ID="IEq11"> <EquationSource Format="TEX">\({\mathbb {B}}^n \subset {\mathbb {C}}^n\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msup> <mrow> <mi mathvariant="double-struck">B</mi> </mrow> <mi>n</mi> </msup> <mo>⊂</mo> <msup> <mrow> <mi mathvariant="double-struck">C</mi> </mrow> <mi>n</mi> </msup> </mrow> </math></EquationSource> </InlineEquation>. We produce sampling expansions of functions <InlineEquation ID="IEq12"> <EquationSource Format="TEX">\(f \in L^2 H(\Omega )\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>f</mi> <mo>∈</mo> <msup> <mi>L</mi> <mn>2</mn> </msup> <mi>H</mi> <mrow> <mo stretchy="false">(</mo> <mi mathvariant="normal">Ω</mi> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation> associated to infinite sequences <InlineEquation ID="IEq13"> <EquationSource Format="TEX">\(\{ \zeta _k \}_{k \ge 0} \subset \Omega \)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mrow> <mo stretchy="false">{</mo> <msub> <mi>ζ</mi> <mi>k</mi> </msub> <mo stretchy="false">}</mo> </mrow> <mrow> <mi>k</mi> <mo>≥</mo> <mn>0</mn> </mrow> </msub> <mo>⊂</mo> <mi mathvariant="normal">Ω</mi> </mrow> </math></EquationSource> </InlineEquation>, by starting from complete orthonormal systems <InlineEquation ID="IEq14"> <EquationSource Format="TEX">\(\{ \phi _\nu \}_{\nu \ge 0} \subset L^2 H(\Omega )\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mrow> <mo stretchy="false">{</mo> <msub> <mi>ϕ</mi> <mi>ν</mi> </msub> <mo stretchy="false">}</mo> </mrow> <mrow> <mi>ν</mi> <mo>≥</mo> <mn>0</mn> </mrow> </msub> <mo>⊂</mo> <msup> <mi>L</mi> <mn>2</mn> </msup> <mi>H</mi> <mrow> <mo stretchy="false">(</mo> <mi mathvariant="normal">Ω</mi> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation> and approximating each <InlineEquation ID="IEq15"> <EquationSource Format="TEX">\(\phi _\nu \)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>ϕ</mi> <mi>ν</mi> </msub> </math></EquationSource> </InlineEquation> uniformly on <InlineEquation ID="IEq16"> <EquationSource Format="TEX">\(\Omega \)</EquationSource> <EquationSource Format="MATHML"><math> <mi mathvariant="normal">Ω</mi> </math></EquationSource> </InlineEquation> by a linear combination of reproducing kernels. The means to said approximation are provided by the Faber-Kaczmarz-Mycielski algorithm <InlineEquation ID="IEq17"> <EquationSource Format="TEX">\({\mathscr {A}}(h)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi mathvariant="script">A</mi> <mo stretchy="false">(</mo> <mi>h</mi> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation> learning (cf. [<CitationRef CitationID="CR23">23</CitationRef>]) from the data <InlineEquation ID="IEq18"> <EquationSource Format="TEX">\(\big \{ \big ( \zeta _k \,, \, \phi _\nu (\zeta _k ) \big ) \big \}_{k \ge 0}\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mrow> <mo maxsize="1.2em" minsize="1.2em" stretchy="true">{</mo> </mrow> <mrow> <mo maxsize="1.2em" minsize="1.2em" stretchy="true">(</mo> </mrow> <msub> <mi>ζ</mi> <mi>k</mi> </msub> <mspace width="0.166667em" /> <mo>,</mo> <mspace width="0.166667em" /> <msub> <mi>ϕ</mi> <mi>ν</mi> </msub> <mrow> <mo stretchy="false">(</mo> <msub> <mi>ζ</mi> <mi>k</mi> </msub> <mo stretchy="false">)</mo> </mrow> <mrow> <mo maxsize="1.2em" minsize="1.2em" stretchy="true">)</mo> </mrow> <msub> <mrow> <mo maxsize="1.2em" minsize="1.2em" stretchy="true">}</mo> </mrow> <mrow> <mi>k</mi> <mo>≥</mo> <mn>0</mn> </mrow> </msub> </mrow> </math></EquationSource> </InlineEquation> and producing an approximating sequence <InlineEquation ID="IEq19"> <EquationSource Format="TEX">\(\big \{ {\mathscr {J}}_k \, \phi _\nu \big \}_{k \ge 0} \subset L^2 H(\Omega )\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mrow> <mo maxsize="1.2em" minsize="1.2em" stretchy="true">{</mo> </mrow> <msub> <mi mathvariant="script">J</mi> <mi>k</mi> </msub> <mspace width="0.166667em" /> <msub> <mi>ϕ</mi> <mi>ν</mi> </msub> <msub> <mrow> <mo maxsize="1.2em" minsize="1.2em" stretchy="true">}</mo> </mrow> <mrow> <mi>k</mi> <mo>≥</mo> <mn>0</mn> </mrow> </msub> <mo>⊂</mo> <msup> <mi>L</mi> <mn>2</mn> </msup> <mi>H</mi> <mrow> <mo stretchy="false">(</mo> <mi mathvariant="normal">Ω</mi> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation>.</p>

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Holomorphic \(L^2\) Signals of Several Complex Variables

  • Elisabetta Barletta,
  • Fabio Bonsignorio,
  • Sorin Dragomir,
  • Francesco Esposito,
  • Enrica Zereik

摘要

Following the line of thought by P. Bouboulis & S. Theodoridis, [6], we take up a program of recovering kernel methods (as employed in signal analysis and machine learning theory) from real RKHS and kernels, to the complex domain. We solve the maximum problem \(\sup \, \big \{ \sum _{j=1}^p \big | f( z_j ) \big |^2 \,: \, \Vert f \Vert ^2 \le E \big \}\) sup { j = 1 p | f ( z j ) | 2 : f 2 E } in the complex RKHS of holomorphic \(L^2\) L 2 functions \(f: \Omega \rightarrow {\mathbb {C}}\) f : Ω C , for any bounded domain \(\Omega \subset {\mathbb {C}}^n\) Ω C n and any finite set of points \(z_1 \,, \, \cdots \,, \, z_p \in \Omega \) z 1 , , z p Ω , and apply the result to the space \(L^2 H({\mathbb {B}}^n )\) L 2 H ( B n ) of holomorphic \(L^2\) L 2 functions on the unit ball \({\mathbb {B}}^n \subset {\mathbb {C}}^n\) B n C n . We produce sampling expansions of functions \(f \in L^2 H(\Omega )\) f L 2 H ( Ω ) associated to infinite sequences \(\{ \zeta _k \}_{k \ge 0} \subset \Omega \) { ζ k } k 0 Ω , by starting from complete orthonormal systems \(\{ \phi _\nu \}_{\nu \ge 0} \subset L^2 H(\Omega )\) { ϕ ν } ν 0 L 2 H ( Ω ) and approximating each \(\phi _\nu \) ϕ ν uniformly on \(\Omega \) Ω by a linear combination of reproducing kernels. The means to said approximation are provided by the Faber-Kaczmarz-Mycielski algorithm \({\mathscr {A}}(h)\) A ( h ) learning (cf. [23]) from the data \(\big \{ \big ( \zeta _k \,, \, \phi _\nu (\zeta _k ) \big ) \big \}_{k \ge 0}\) { ( ζ k , ϕ ν ( ζ k ) ) } k 0 and producing an approximating sequence \(\big \{ {\mathscr {J}}_k \, \phi _\nu \big \}_{k \ge 0} \subset L^2 H(\Omega )\) { J k ϕ ν } k 0 L 2 H ( Ω ) .