• Title of article

    Conditional probability of derangements and fixed points

  • Author/Authors

    Gutmann ، Sam Department of Mathematics - Northeastern University , Mixer ، Mark School of Computing and Data Science - Wentworth Institute of Technology , Morrow ، Steven School of Computing and Data Science - Wentworth Institute of Technology

  • From page
    11
  • To page
    26
  • Abstract
    The probability that a random permutation in S_n is a derangement is well known to be \displaystyle\sum\limits_{j=0}^n (-1)^j \frac{1}{j!}. In this paper, we consider the conditional probability that the (k+1)^{st} point is fixed, given there are no fixed points in the first k points. We prove that when n \neq 3 and k \neq 1, this probability is a decreasing function of both k and n. Furthermore, it is proved that this conditional probability is well approximated by $\frac{1}{n} - \frac{k}{n^2(n-1)}. Similar results are also obtained about the more general conditional probability that the (k+1)^{st} point is fixed, given that there are exactly d fixed points in the first k points.
  • Keywords
    derangement , Fixed Point , probability
  • Journal title
    Transactions on Combinatorics
  • Journal title
    Transactions on Combinatorics
  • Record number

    2737701