arXiv subjects
Publications and source records attributed to David Penman.
We study the number of linear extensions of a partial order with a given proportion of comparable pairs of elements, and estimate the maximum and minimum possible numbers. We also consider a random interval partial order on $n$ elements, which has close to a third of the pairs comparable with high probability: we show that the number of linear extensions is $n! \, 2^{-\Theta(n)}$ with high probability.
This paper gives a straightforward self-contained proof of the formula for the variance of the number of comparisons used by the Quicksort sorting algorithm when pivots are chosen uniformly at random. The result has been known for some time but we had not found a single source giving all details of the argument in a self-contained and explicit way. We hope these details may be of interest to students and others wishing to understand this calculation. No originality is claimed for the result.