Published online by Cambridge University Press: 20 November 2018
We prove that for the linear scalar delay differential equation
with non-negative periodic coefficients of period $p\,>\,0$, the stability threshold for the trivial solution is $r\,:=\int_{0}^{p}{\left( b\left( t \right)-a\left( t \right) \right)}dt\,=\,0$, assuming that $b\left( t+1 \right)-a\left( t \right)$ does not change its sign. By constructing a class of explicit examples, we show the counter-intuitive result that, in general, $r\,=\,0$ is not a stability threshold.