The longest increasing subsequences of Luce permutations and permutons

Abstract

We investigate the longest increasing subsequences (LIS) of random permutations distributed under the Luce model with weights $θ_1^{(n)} \ge \ldots \ge θ_n^{(n)}$. Our first main result provides a general formula for the growth rate of the LIS. For example, we get that the LIS of Luce permutations with Sukhatme weights $θ_k^{(n)} = n-k+1$ grows like $\sqrt{n}$. We also give simple conditions for the LIS to be of order $n^β$, for any given $β\in[1/2,1)$. Our second main result states that, if the weights are of the form $θ_k^{(n)} = f\big( (k-1)/n \big)$ for a sufficiently regular function $f$, then the LIS divided by $2\sqrt{n}$ converges in probability to a constant $K(f)$ described by a variational problem. Throughout, we make extensive use of coupling techniques; in particular, to prove our second main result, we argue that Luce random permutations behave similarly to random permutations sampled from the ``Luce permuton''.