arXiv subjects

Doug Wiedemann

Publications and source records attributed to Doug Wiedemann.

2 recordsLinked to original sources

arXiv2021

A Simple Search Problem

A simple problem is studied in which there are N boxes and a prize known to be in one of the boxes. Furthermore, the probability that the prize is in any box is given. It is desired to find the prize with minimal expected work, where it takes one unit of work to open a box and look inside. The paper establishes bounds on the minimal work in terms of the $p=1/2$ Hölder norm of the probability density and in terms of the entropy of the probability density. We also introduce the notion of "Cartesian product" of problems, and determine the asymptotic behavior of the minimal work for the $n$th power of a problem. (This article is a newly typeset version of an internal publication written in 1984. The second author passed away on November 12, 2020, and his estate has approved the submission of this paper.)

math.OC↗

arXiv2007

Equivalence of sparse circulants: the bipartite Ádám problem

We consider n-by-n circulant matrices having entries 0 and 1. Such matrices can be identified with sets of residues mod n, corresponding to the columns in which the top row contains an entry 1. Let A and B be two such matrices, and suppose that the corresponding residue sets S_A and S_B have size at most 3. We prove that the following are equivalent: (1) there are integers u,v mod n, with u a unit, such that S_A = uS_B + v; (2) there are permutation matrices P,Q such that A=PBQ. Our proof relies on some new results about vanishing sums of roots of unity. We give examples showing this result is not always true for denser circulants, as well as results showing it continues to hold in some situations. We also explain how our problem relates to the Adam problem on isomorphisms of circulant directed graphs.

math.CO↗