Continuity properties of solutions to H/sub 2/ and H/sub /spl infin// Riccati equations

In H/sub 2/ and H/sub /spl infin// optimal control (semi-) stabilizing solutions of algebraic Riccati equations play an essential role. It is well-known that these solutions might have discontinuities as a function of the system parameters. The paper shows that these discontinuities are directly linked to nonleft-invertibility and, in contrast to what one might think, unrelated to zeros on the imaginary axis.