<p>For a rational function <i>R</i>, let <InlineEquation ID="IEq1"> <EquationSource Format="TEX">\(N_R(z)=z-\frac{R(z)}{R'(z)}.\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi>N</mi> <mi>R</mi> </msub> <mrow> <mo stretchy="false">(</mo> <mi>z</mi> <mo stretchy="false">)</mo> </mrow> <mo>=</mo> <mi>z</mi> <mo>-</mo> <mfrac> <mrow> <mi>R</mi> <mo stretchy="false">(</mo> <mi>z</mi> <mo stretchy="false">)</mo> </mrow> <mrow> <msup> <mi>R</mi> <mo>′</mo> </msup> <mrow> <mo stretchy="false">(</mo> <mi>z</mi> <mo stretchy="false">)</mo> </mrow> </mrow> </mfrac> <mo>.</mo> </mrow> </math></EquationSource> </InlineEquation> Any such <InlineEquation ID="IEq2"> <EquationSource Format="TEX">\(N_R\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>N</mi> <mi>R</mi> </msub> </math></EquationSource> </InlineEquation> is referred to as a Newton map. We determine all the rational functions <i>R</i> for which <InlineEquation ID="IEq3"> <EquationSource Format="TEX">\(N_R\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>N</mi> <mi>R</mi> </msub> </math></EquationSource> </InlineEquation> has exactly two attracting fixed points, one of which is an exceptional point. Further, if all the repelling fixed points of any such Newton map are with multiplier 2, or the multiplier of the non-exceptional attracting fixed point is at most <InlineEquation ID="IEq4"> <EquationSource Format="TEX">\(\frac{4}{5}\)</EquationSource> <EquationSource Format="MATHML"><math> <mfrac> <mn>4</mn> <mn>5</mn> </mfrac> </math></EquationSource> </InlineEquation>, then its Julia set is shown to be connected. If a polynomial <i>p</i> has exactly two roots, is unicritical but not a monomial, or <InlineEquation ID="IEq5"> <EquationSource Format="TEX">\(p(z)=z(z^n+a)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>p</mi> <mrow> <mo stretchy="false">(</mo> <mi>z</mi> <mo stretchy="false">)</mo> </mrow> <mo>=</mo> <mi>z</mi> <mrow> <mo stretchy="false">(</mo> <msup> <mi>z</mi> <mi>n</mi> </msup> <mo>+</mo> <mi>a</mi> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation> for some <InlineEquation ID="IEq6"> <EquationSource Format="TEX">\(a \in \mathbb {C}\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>a</mi> <mo>∈</mo> <mi mathvariant="double-struck">C</mi> </mrow> </math></EquationSource> </InlineEquation> and <InlineEquation ID="IEq7"> <EquationSource Format="TEX">\(n \ge 1\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>n</mi> <mo>≥</mo> <mn>1</mn> </mrow> </math></EquationSource> </InlineEquation>, then we have proved that the Julia set of <InlineEquation ID="IEq8"> <EquationSource Format="TEX">\(N_{1/p}\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>N</mi> <mrow> <mn>1</mn> <mo stretchy="false">/</mo> <mi>p</mi> </mrow> </msub> </math></EquationSource> </InlineEquation> is totally disconnected. For the McMullen map <InlineEquation ID="IEq9"> <EquationSource Format="TEX">\(f_{\lambda }(z)=z^m - \frac{\lambda }{z^n}\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi>f</mi> <mi>λ</mi> </msub> <mrow> <mo stretchy="false">(</mo> <mi>z</mi> <mo stretchy="false">)</mo> </mrow> <mo>=</mo> <msup> <mi>z</mi> <mi>m</mi> </msup> <mo>-</mo> <mfrac> <mi>λ</mi> <msup> <mi>z</mi> <mi>n</mi> </msup> </mfrac> </mrow> </math></EquationSource> </InlineEquation>, <InlineEquation ID="IEq10"> <EquationSource Format="TEX">\(\lambda \in \mathbb {C}{\setminus } \{0\}\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>λ</mi> <mo>∈</mo> <mi mathvariant="double-struck">C</mi> <mo lspace="0.15em" rspace="0.15em" stretchy="false">\</mo> <mo stretchy="false">{</mo> <mn>0</mn> <mo stretchy="false">}</mo> </mrow> </math></EquationSource> </InlineEquation> and <InlineEquation ID="IEq11"> <EquationSource Format="TEX">\(m,n \ge 1\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>m</mi> <mo>,</mo> <mi>n</mi> <mo>≥</mo> <mn>1</mn> </mrow> </math></EquationSource> </InlineEquation>, we have proved that the Julia set of <InlineEquation ID="IEq12"> <EquationSource Format="TEX">\(N_{f_\lambda }\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>N</mi> <msub> <mi>f</mi> <mi>λ</mi> </msub> </msub> </math></EquationSource> </InlineEquation> is connected and is invariant under rotations about the origin of order <InlineEquation ID="IEq13"> <EquationSource Format="TEX">\(m+n\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>m</mi> <mo>+</mo> <mi>n</mi> </mrow> </math></EquationSource> </InlineEquation>. All the connected Julia sets mentioned above are found to be locally connected.</p>

错误:搜索内容不能为空,请输入英文关键词
错误:关键词超出字数限制,请精简
高级检索

Newton’s Method Applied to Rational Functions: Fixed Points and Julia Sets

  • Tarakanta Nayak,
  • Soumen Pal,
  • Pooja Phogat

摘要

For a rational function R, let \(N_R(z)=z-\frac{R(z)}{R'(z)}.\) N R ( z ) = z - R ( z ) R ( z ) . Any such \(N_R\) N R is referred to as a Newton map. We determine all the rational functions R for which \(N_R\) N R has exactly two attracting fixed points, one of which is an exceptional point. Further, if all the repelling fixed points of any such Newton map are with multiplier 2, or the multiplier of the non-exceptional attracting fixed point is at most \(\frac{4}{5}\) 4 5 , then its Julia set is shown to be connected. If a polynomial p has exactly two roots, is unicritical but not a monomial, or \(p(z)=z(z^n+a)\) p ( z ) = z ( z n + a ) for some \(a \in \mathbb {C}\) a C and \(n \ge 1\) n 1 , then we have proved that the Julia set of \(N_{1/p}\) N 1 / p is totally disconnected. For the McMullen map \(f_{\lambda }(z)=z^m - \frac{\lambda }{z^n}\) f λ ( z ) = z m - λ z n , \(\lambda \in \mathbb {C}{\setminus } \{0\}\) λ C \ { 0 } and \(m,n \ge 1\) m , n 1 , we have proved that the Julia set of \(N_{f_\lambda }\) N f λ is connected and is invariant under rotations about the origin of order \(m+n\) m + n . All the connected Julia sets mentioned above are found to be locally connected.