<p>In this paper, we study <i>sums of translates</i> on the real axis. These functions generalize logarithms of weighted algebraic polynomials. Namely, we are dealing with functions<Equation ID="Equ1"> <EquationSource Format="TEX">\((F\text{y},t) := J(t) + \sum _{j=1}^n K_j(t-y_j), \quad \text{y} := (y1,\ldots,y_n), \ y_1 \le \cdots \le y_n, \ t \in \mathbb{R},\)</EquationSource> <EquationSource Format="MATHML"><math display="block"> <mrow> <mrow> <mo stretchy="false">(</mo> <mi>F</mi> <mtext>y</mtext> <mo>,</mo> <mi>t</mi> <mo stretchy="false">)</mo> </mrow> <mo>:</mo> <mo>=</mo> <mi>J</mi> <mrow> <mo stretchy="false">(</mo> <mi>t</mi> <mo stretchy="false">)</mo> </mrow> <mo>+</mo> <munderover> <mo>∑</mo> <mrow> <mi>j</mi> <mo>=</mo> <mn>1</mn> </mrow> <mi>n</mi> </munderover> <msub> <mi>K</mi> <mi>j</mi> </msub> <mrow> <mo stretchy="false">(</mo> <mi>t</mi> <mo>-</mo> <msub> <mi>y</mi> <mi>j</mi> </msub> <mo stretchy="false">)</mo> </mrow> <mo>,</mo> <mspace width="1em" /> <mtext>y</mtext> <mo>:</mo> <mo>=</mo> <mrow> <mo stretchy="false">(</mo> <mi>y</mi> <mn>1</mn> <mo>,</mo> <mo>…</mo> <mo>,</mo> <msub> <mi>y</mi> <mi>n</mi> </msub> <mo stretchy="false">)</mo> </mrow> <mo>,</mo> <mspace width="4pt" /> <msub> <mi>y</mi> <mn>1</mn> </msub> <mo>≤</mo> <mo>⋯</mo> <mo>≤</mo> <msub> <mi>y</mi> <mi>n</mi> </msub> <mo>,</mo> <mspace width="4pt" /> <mi>t</mi> <mo>∈</mo> <mi mathvariant="double-struck">R</mi> <mo>,</mo> </mrow> </math></EquationSource> </Equation>where the <i>kernels</i><InlineEquation ID="IEq1"> <EquationSource Format="TEX">\(K_1,\ldots,K_n\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi>K</mi> <mn>1</mn> </msub> <mo>,</mo> <mo>…</mo> <mo>,</mo> <msub> <mi>K</mi> <mi>n</mi> </msub> </mrow> </math></EquationSource> </InlineEquation> are concave on <InlineEquation ID="IEq2"> <EquationSource Format="TEX">\((-\infty,0)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mo stretchy="false">(</mo> <mo>-</mo> <mi>∞</mi> <mo>,</mo> <mn>0</mn> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation> and on <InlineEquation ID="IEq3"> <EquationSource Format="TEX">\((0,\infty)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mo stretchy="false">(</mo> <mn>0</mn> <mo>,</mo> <mi>∞</mi> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation>, having a singularity at <InlineEquation ID="IEq4"> <EquationSource Format="TEX">\(0\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mn>0</mn> </mrow> </math></EquationSource> </InlineEquation>, and <InlineEquation ID="IEq5"> <EquationSource Format="TEX">\(J\colon \mathbb{R}\to \mathbb{R}\cup\{-\infty\}\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>J</mi> <mo lspace="0pt">:</mo> <mi mathvariant="double-struck">R</mi> <mo stretchy="false">→</mo> <mi mathvariant="double-struck">R</mi> <mo>∪</mo> <mo stretchy="false">{</mo> <mo>-</mo> <mi>∞</mi> <mo stretchy="false">}</mo> </mrow> </math></EquationSource> </InlineEquation> isthe <i>field function</i>. We consider "local maxima"<Equation ID="Equ2"> <EquationSource Format="TEX">\(m_0(\text{y}) := \sup _{t \in (-\infty, y_1]} F(\text{y}, t), \quad m_n(\text{y}) := \sup _{t \in [y_n, \infty)} F(\text{y}, t),\)</EquationSource> <EquationSource Format="MATHML"><math display="block"> <mrow> <msub> <mi>m</mi> <mn>0</mn> </msub> <mrow> <mo stretchy="false">(</mo> <mtext>y</mtext> <mo stretchy="false">)</mo> </mrow> <mo>:</mo> <mo>=</mo> <munder> <mo movablelimits="true">sup</mo> <mrow> <mi>t</mi> <mo>∈</mo> <mo stretchy="false">(</mo> <mo>-</mo> <mi>∞</mi> <mo>,</mo> <msub> <mi>y</mi> <mn>1</mn> </msub> <mo stretchy="false">]</mo> </mrow> </munder> <mi>F</mi> <mrow> <mo stretchy="false">(</mo> <mtext>y</mtext> <mo>,</mo> <mi>t</mi> <mo stretchy="false">)</mo> </mrow> <mo>,</mo> <mspace width="1em" /> <msub> <mi>m</mi> <mi>n</mi> </msub> <mrow> <mo stretchy="false">(</mo> <mtext>y</mtext> <mo stretchy="false">)</mo> </mrow> <mo>:</mo> <mo>=</mo> <munder> <mo movablelimits="true">sup</mo> <mrow> <mi>t</mi> <mo>∈</mo> <mo stretchy="false">[</mo> <msub> <mi>y</mi> <mi>n</mi> </msub> <mo>,</mo> <mi>∞</mi> <mo stretchy="false">)</mo> </mrow> </munder> <mi>F</mi> <mrow> <mo stretchy="false">(</mo> <mtext>y</mtext> <mo>,</mo> <mi>t</mi> <mo stretchy="false">)</mo> </mrow> <mo>,</mo> </mrow> </math></EquationSource> </Equation><Equation ID="Equ5"> <EquationSource Format="TEX">\(m_j(\text{y}) := \sup _{t \in [y_j, y_{j+1}]} F(\text{y}, t), \quad j = 1,\ldots,n-1, \)</EquationSource> <EquationSource Format="MATHML"><math display="block"> <mrow> <msub> <mi>m</mi> <mi>j</mi> </msub> <mrow> <mo stretchy="false">(</mo> <mtext>y</mtext> <mo stretchy="false">)</mo> </mrow> <mo>:</mo> <mo>=</mo> <munder> <mo movablelimits="true">sup</mo> <mrow> <mi>t</mi> <mo>∈</mo> <mo stretchy="false">[</mo> <msub> <mi>y</mi> <mi>j</mi> </msub> <mo>,</mo> <msub> <mi>y</mi> <mrow> <mi>j</mi> <mo>+</mo> <mn>1</mn> </mrow> </msub> <mo stretchy="false">]</mo> </mrow> </munder> <mi>F</mi> <mrow> <mo stretchy="false">(</mo> <mtext>y</mtext> <mo>,</mo> <mi>t</mi> <mo stretchy="false">)</mo> </mrow> <mo>,</mo> <mspace width="1em" /> <mi>j</mi> <mo>=</mo> <mn>1</mn> <mo>,</mo> <mo>…</mo> <mo>,</mo> <mi>n</mi> <mo>-</mo> <mn>1</mn> <mo>,</mo> </mrow> </math></EquationSource> </Equation>and the difference function<Equation ID="Equ4"> <EquationSource Format="TEX">\((D\text{y}) := (m_1\text({y})-m_0\text({y}), m_2\text({y})-m_1\text({y}), \cdots, m_n\text({y})-m_{n-1}\text({y})). \)</EquationSource> <EquationSource Format="MATHML"><math display="block"> <mrow> <mrow> <mo stretchy="false">(</mo> <mi>D</mi> <mtext>y</mtext> <mo stretchy="false">)</mo> </mrow> <mo>:</mo> <mo>=</mo> <mrow> <mo stretchy="false">(</mo> <msub> <mi>m</mi> <mn>1</mn> </msub> <mtext>(</mtext> <mi>y</mi> <mo stretchy="false">)</mo> </mrow> <mo>-</mo> <msub> <mi>m</mi> <mn>0</mn> </msub> <mrow> <mtext>(</mtext> <mi>y</mi> <mo stretchy="false">)</mo> <mo>,</mo> </mrow> <msub> <mi>m</mi> <mn>2</mn> </msub> <mrow> <mtext>(</mtext> <mi>y</mi> <mo stretchy="false">)</mo> <mo>-</mo> </mrow> <msub> <mi>m</mi> <mn>1</mn> </msub> <mrow> <mtext>(</mtext> <mi>y</mi> <mo stretchy="false">)</mo> <mo>,</mo> <mo>⋯</mo> <mo>,</mo> </mrow> <msub> <mi>m</mi> <mi>n</mi> </msub> <mrow> <mtext>(</mtext> <mi>y</mi> <mo stretchy="false">)</mo> <mo>-</mo> </mrow> <msub> <mi>m</mi> <mrow> <mi>n</mi> <mo>-</mo> <mn>1</mn> </mrow> </msub> <mtext>(</mtext> <mi>y</mi> <mrow> <mo stretchy="false">)</mo> <mo stretchy="false">)</mo> </mrow> <mo>.</mo> </mrow> </math></EquationSource> </Equation>We prove that, under certain assumptions on the kernels and the field, <InlineEquation ID="IEq10"> <EquationSource Format="TEX">\(D\)</EquationSource> <EquationSource Format="MATHML"><math> <mi>D</mi> </math></EquationSource> </InlineEquation> is a homeomorphism between its domain and <InlineEquation ID="IEq11"> <EquationSource Format="TEX">\(\mathbb{R}^n\)</EquationSource> <EquationSource Format="MATHML"><math> <msup> <mrow> <mi mathvariant="double-struck">R</mi> </mrow> <mi>n</mi> </msup> </math></EquationSource> </InlineEquation>. </p>

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Homeomorphism theorem for sums of translates on the real axis

  • T. M. Nikiforova

摘要

In this paper, we study sums of translates on the real axis. These functions generalize logarithms of weighted algebraic polynomials. Namely, we are dealing with functions \((F\text{y},t) := J(t) + \sum _{j=1}^n K_j(t-y_j), \quad \text{y} := (y1,\ldots,y_n), \ y_1 \le \cdots \le y_n, \ t \in \mathbb{R},\) ( F y , t ) : = J ( t ) + j = 1 n K j ( t - y j ) , y : = ( y 1 , , y n ) , y 1 y n , t R , where the kernels \(K_1,\ldots,K_n\) K 1 , , K n are concave on \((-\infty,0)\) ( - , 0 ) and on \((0,\infty)\) ( 0 , ) , having a singularity at \(0\) 0 , and \(J\colon \mathbb{R}\to \mathbb{R}\cup\{-\infty\}\) J : R R { - } isthe field function. We consider "local maxima" \(m_0(\text{y}) := \sup _{t \in (-\infty, y_1]} F(\text{y}, t), \quad m_n(\text{y}) := \sup _{t \in [y_n, \infty)} F(\text{y}, t),\) m 0 ( y ) : = sup t ( - , y 1 ] F ( y , t ) , m n ( y ) : = sup t [ y n , ) F ( y , t ) , \(m_j(\text{y}) := \sup _{t \in [y_j, y_{j+1}]} F(\text{y}, t), \quad j = 1,\ldots,n-1, \) m j ( y ) : = sup t [ y j , y j + 1 ] F ( y , t ) , j = 1 , , n - 1 , and the difference function \((D\text{y}) := (m_1\text({y})-m_0\text({y}), m_2\text({y})-m_1\text({y}), \cdots, m_n\text({y})-m_{n-1}\text({y})). \) ( D y ) : = ( m 1 ( y ) - m 0 ( y ) , m 2 ( y ) - m 1 ( y ) , , m n ( y ) - m n - 1 ( y ) ) . We prove that, under certain assumptions on the kernels and the field, \(D\) D is a homeomorphism between its domain and \(\mathbb{R}^n\) R n .