Department of Mathematics

Indian Institute of Science

Bangalore 560 012






Tulasi Ram Reddy A
Affiliation : IISc

Subject Area






Department of Mathematics, Lecture Hall I




11:00 a.m.




January 27, 2016 (Wednesday)



"On critical points of random polynomials and spectrum of certain
                products of random matrices"


In the first part we study critical points of random polynomials. We choose two deterministic sequences of complex numbers,whose empirical measures converge to the same probability measure in complex plane. We make a sequence of polynomials whose zeros are chosen from either of sequences at random. We show that the limiting empirical measure of zeros and critical points agree for these polynomials. As a consequence we show that when we randomly perturb the zeros of a deterministic sequence of polynomials, the limiting empirical measures of zeros and critical points agree. This result can be interpreted as an extension of earlier results where randomness is reduced. Pemantle and Rivin initiated the study of critical points of random polynomials. Kabluchko proved the result considering the zeros to be i.i.d. random variables. In the second part we deal with the spectrum of products of Ginibre matrices. Exact eigenvalue density is known for a very few matrix ensembles. For the known ones they often lead to determinantal point process. Let X_1,X_2,...,X_k be i.i.d matrices of size nxn whose entries are independent complex Gaussian random variables. We derive the eigenvalue density for matrices of the form Y_1.Y_2....Y_n, where each Y_i = X_i or (X_i)^{-1}. We show that the eigenvalues form a determinantal point process. The case where k=2, Y_1=X_1,Y_2=X_2^{-1} was derived earlier by Krishnapur. The case where Y_i =X_i for all i=1,2,...,n, was derived by Akemann and Burda. These two known cases can be obtained as special cases of our result.