vIn particular, consider
q
q Then
the closed-loop system is stable for every such D iff
•
•
• has no
zero in the closed right-half plane.
• Hence the
stability region is given by
•2+ d11+ d22 >0, 1+d11+d22+(1+a2)d11d22>0
• The system is unstable
with
• d11 =-d22 = (1+a2)-1/2