A multivariable feedback systemy¯(s)=G(s)x(s).x¯(s)=ū(s) −F(s)y(s) is considered, whereG(sδ (gkl(s) is then×nplant transfer matrix andf(s) = diag (f1) ⃛f2(s) ⃛fn(s)). By imposing some restrictions on the structure ofG(s), we may use the eigenvalues λj(s), 1≤j≤nofG(s) to infer the stability of the closed-loop system in an arbitrary rectangular region Φ δ{F