On the stability of low-order perturbed polynomials

It is shown that for low-order perturbed continuous system polynomials (N⩽6), stability can be guaranteed by checking very simple conditions based on the Hermite-Biehler theorem. For N ⩽5 no numerical computation of the roots is required to check stability. For N=6, one root of a third-order polynomial needs to be found, with the rest of the conditions reducing to simple algorithmic relationships. The result is illustrated by numerical examples