Singularity of $\{\pm 1\}$-matrices and asymptotics of the number of threshold functions

Anwar A. Irmatov

Published 2020-04-05Version 1

Two results concerning the number of threshold functions $P(2, n)$ and the probability ${\mathbb P}_n$ that a random $n\times n$ Bernoulli matrix is singular are established. We introduce a supermodular function $\eta^{\bigstar}_n : 2^{{\bf RP}^n}_{fin} \to \mathbb{Z}_{\geq 0},$ defined on finite subsets of ${\bf RP}^n,$ that allows us to obtain a lower bound for $P(2, n)$ in terms of ${\mathbb P}_{n+1}.$ This, together with L.Schl\"afli's famous upper bound, give us asymptotics $$P(2, n) \thicksim 2 {2^n-1 \choose n},\quad n\to \infty.$$ Also, the validity of the long-standing conjecture concerning ${\mathbb P}_n$ is proved: $$\mathbb{P}_n \thicksim n^22^{1-n}, \quad n\to \infty .$$