<p>Generalizing a formula of Stanley, we prove combinatorially that the probability that <InlineEquation ID="IEq1"> <EquationSource Format="TEX">\(1, 2, \dots , k\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mn>1</mn> <mo>,</mo> <mn>2</mn> <mo>,</mo> <mo>⋯</mo> <mo>,</mo> <mi>k</mi> </mrow> </math></EquationSource> </InlineEquation> are contained in the same cycle of a product of two random <i>n</i>-cycles is <Equation ID="Equ1"> <EquationSource Format="TEX">\(\frac{1}{k} + \frac{4 (-1)^n}{ \left( {\begin{array}{c}2k\\ k\end{array}}\right) } \sum _{\begin{array}{c} 1 \le i \le k-1 \\ i \not \equiv n \bmod 2 \end{array}} \left( {\begin{array}{c}2k-1\\ k+i\end{array}}\right) \left( \frac{1}{n+i+1} - \frac{1}{n-i}\right) .\)</EquationSource> <EquationSource Format="MATHML"><math display="block"> <mrow> <mfrac> <mn>1</mn> <mi>k</mi> </mfrac> <mo>+</mo> <mfrac> <mrow> <mn>4</mn> <msup> <mrow> <mo stretchy="false">(</mo> <mo>-</mo> <mn>1</mn> <mo stretchy="false">)</mo> </mrow> <mi>n</mi> </msup> </mrow> <mfenced close=")" open="("> <mrow> <mtable> <mtr> <mtd> <mrow> <mn>2</mn> <mi>k</mi> </mrow> </mtd> </mtr> <mtr> <mtd> <mrow> <mrow /> <mi>k</mi> </mrow> </mtd> </mtr> </mtable> </mrow> </mfenced> </mfrac> <munder> <mo>∑</mo> <mrow> <mtable> <mtr> <mtd> <mrow> <mn>1</mn> <mo>≤</mo> <mi>i</mi> <mo>≤</mo> <mi>k</mi> <mo>-</mo> <mn>1</mn> </mrow> </mtd> </mtr> <mtr> <mtd> <mrow> <mrow /> <mi>i</mi> <mo>≢</mo> <mi>n</mi> <mspace width="0.277778em" /> <mo>mod</mo> <mspace width="0.277778em" /> <mn>2</mn> </mrow> </mtd> </mtr> </mtable> </mrow> </munder> <mfenced close=")" open="("> <mrow> <mtable> <mtr> <mtd> <mrow> <mn>2</mn> <mi>k</mi> <mo>-</mo> <mn>1</mn> </mrow> </mtd> </mtr> <mtr> <mtd> <mrow> <mrow /> <mi>k</mi> <mo>+</mo> <mi>i</mi> </mrow> </mtd> </mtr> </mtable> </mrow> </mfenced> <mfenced close=")" open="("> <mfrac> <mn>1</mn> <mrow> <mi>n</mi> <mo>+</mo> <mi>i</mi> <mo>+</mo> <mn>1</mn> </mrow> </mfrac> <mo>-</mo> <mfrac> <mn>1</mn> <mrow> <mi>n</mi> <mo>-</mo> <mi>i</mi> </mrow> </mfrac> </mfenced> <mo>.</mo> </mrow> </math></EquationSource> </Equation></p>

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Coalescence Probabilities of Cycle Products

  • Holden Mui

摘要

Generalizing a formula of Stanley, we prove combinatorially that the probability that \(1, 2, \dots , k\) 1 , 2 , , k are contained in the same cycle of a product of two random n-cycles is \(\frac{1}{k} + \frac{4 (-1)^n}{ \left( {\begin{array}{c}2k\\ k\end{array}}\right) } \sum _{\begin{array}{c} 1 \le i \le k-1 \\ i \not \equiv n \bmod 2 \end{array}} \left( {\begin{array}{c}2k-1\\ k+i\end{array}}\right) \left( \frac{1}{n+i+1} - \frac{1}{n-i}\right) .\) 1 k + 4 ( - 1 ) n 2 k k 1 i k - 1 i n mod 2 2 k - 1 k + i 1 n + i + 1 - 1 n - i .