Unitary Equivalence to a Complex Symmetric Matrix: A Modulus Criterion

We develop a procedure for determining whether a square complex matrix is unitarily equivalent to a complex symmetric (i.e., self-transpose) matrix. We compare our approach to several existing methods [1, 19, 20] and present a number of examples

Unitary Equivalence to a Complex Symmetric Matrix: Low Dimensions

A matrix T∈Mn(C) is UECSM if it is unitarily equivalent to a complex symmetric (i.e., self-transpose) matrix. We develop several techniques for studying this property in dimensions three and four. Among other things, we completely characterize 4×4 nilpotent matrices which are UECSM and we settle an open problem which has lingered in the 3×3 case. We conclude with a discussion concerning a crucial difference which makes dimension three so different from dimensions four and above

Quotient Sets and Diophantine Equations

Quotient sets U / U = {u / u¹: u, u¹ ϵ U} have been considered several times before in the MONTHLY. We consider more general quotient sets U / V and we apply our results to certain simultaneous Diophantine equations with side constraints

On the Norm Closure Problem for Complex Symmetric Operators

We prove that the set of all complex symmetric operators on a separable, infinite-dimensional Hilbert space is not norm closed