7 papers
On the exponential rate of the condition number of Fourier submatrices and Vandermonde matrices
Rikhav Shah, John Urschel
The discrete Fourier transform matrix is one of the most important matrices in linear algebra, and submatrices of it arise in a variety of applications. Though the discrete Fourier…
The largest 5th pivot may be the root of a 61st degree polynomial
James Chen, Alan Edelman, John Urschel
This paper introduces a number of new techniques in the study of the famous question from numerical linear algebra: what is the largest possible growth factor when performing Gauss…
Nodal Count for Orthogonally Invariant Ensembles
Lior Alon, Dan Mikulincer, John Urschel
We investigate the nodal count of eigenvectors of random matrices interpreted as operators on signed complete graphs. Our focus is on orthogonally invariant ensembles, with particu…
On the Maximum Spread of Non-Negative Matrices
Susie Lu, John Urschel
Given a directed graph , the spread of is the largest distance between any two eigenvalues of its adjacency matrix. In 2022, Breen, Riasanovsky, Tait, and Urschel asked what…
A Class of Optimal Directed Graphs for Network Synchronization
Susie Lu, John Urschel, Ji Liu
In a paper by Nishikawa and Motter, a quantity called the normalized spread of the Laplacian eigenvalues is used to measure the synchronizability of certain network dynamics. Throu…
Estimating the numerical range with a Krylov subspace
Cecilia Chen, John Urschel
Krylov subspace methods are a powerful tool for efficiently solving high-dimensional linear algebra problems. In this work, we study the approximation quality that a Krylov subspac…