Intriguing Patterns in the Roots of the Derivatives of some Random Polynomials

Our observations show that the sets of real (respectively complex) roots of the derivatives of some classical families of random polynomials admit a rich variety of patterns looking like discretized curves. To bring out the shapes of the suggested curves, we introduce an original use of fractional derivatives. Then we set several conjectures and outline a strategy to explain the presented phenomena. This strategy is based on asymptotic geometric properties of the corresponding complex critical points sets.Nos observations montrent que les enembles de racines reelles (resp. complexes) des derivees de certaines familles de polynomes aleatoires ont une riche varietes motifs structures qui ressemblent a des courbes discretisees. Pour faire clairement apparaitre ces courbes, nous avons recours a une utilisation originale des derivees fractionnaires. Nous posons ensuite des conjectures et proposons une strategie pour expliquer les phenomenes observes. Celle-ci est basee sur des proprietes de symetrie asymptotique de l'ensemble des points critiques de nos polynomes quand leur degre tend vers l'infini

Approximating the Permanent of a Random Matrix with Vanishing Mean

We show an algorithm for computing the permanent of a random matrix with vanishing mean in quasi-polynomial time. Among special cases are the Gaussian, and biased-Bernoulli random matrices with mean 1/lnln(n)^{1/8}. In addition, we can compute the permanent of a random matrix with mean 1/poly(ln(n)) in time 2^{O(n^{\eps})} for any small constant \eps>0. Our algorithm counters the intuition that the permanent is hard because of the "sign problem" - namely the interference between entries of a matrix with different signs. A major open question then remains whether one can provide an efficient algorithm for random matrices of mean 1/poly(n), whose conjectured #P-hardness is one of the baseline assumptions of the BosonSampling paradigm

Distribution of roots of random real generalized polynomials

The average density of zeros for monic generalized polynomials, $P_n(z)=\phi(z)+\sum_{k=1}^nc_kf_k(z)$, with real holomorphic $\phi ,f_k$ and real Gaussian coefficients is expressed in terms of correlation functions of the values of the polynomial and its derivative. We obtain compact expressions for both the regular component (generated by the complex roots) and the singular one (real roots) of the average density of roots. The density of the regular component goes to zero in the vicinity of the real axis like $|\hbox{\rm Im}\,z|$. We present the low and high disorder asymptotic behaviors. Then we particularize to the large $n$ limit of the average density of complex roots of monic algebraic polynomials of the form $P_n(z) = z^n +\sum_{k=1}^{n}c_kz^{n-k}$ with real independent, identically distributed Gaussian coefficients having zero mean and dispersion $\delta = \frac 1{\sqrt{n\lambda}}$. The average density tends to a simple, {\em universal} function of $\xi={2n}{\log |z|}$ and $\lambda$ in the domain $\xi\coth \frac{\xi}{2}\ll n|\sin \arg (z)|$ where nearly all the roots are located for large $n$.Comment: 17 pages, Revtex. To appear in J. Stat. Phys. Uuencoded gz-compresed tarfile (.66MB) containing 8 Postscript figures is available by e-mail from [email protected]

The kissing polynomials and their Hankel determinants

We study a family of polynomials that are orthogonal with respect to the weight function $e^{i\omega x}$ in $[-1,1]$, where $\omega\geq 0$. Since this weight function is complex-valued and, for large $\omega$, highly oscillatory, many results in the classical theory of orthogonal polynomials do not apply. In particular, the polynomials need not exist for all values of the parameter $\omega$, and, once they do, their roots lie in the complex plane. Our results are based on analysing the Hankel determinants of these polynomials, reformulated in terms of high-dimensional oscillatory integrals which are amenable to asymptotic analysis. This analysis yields existence of the even-degree polynomials for large values of $\omega$, an asymptotic expansion of the polynomials in terms of rescaled Laguerre polynomials near $\pm 1$ and a description of the intricate structure of the roots of the Hankel determinants in the complex plane. This work is motivated by the design of efficient quadrature schemes for highly oscillatory integrals.Comment: 31 pages, 11 figures. Revised version, Section 8 edite