  The issues of robust stability for two types of uncertain fractional-order
systems of order $\alpha \in (0,1)$ are dealt with in this paper. For the
polytope-type uncertainty case, a less conservative sufficient condition of
robust stability is given; for the norm-bounded uncertainty case, a sufficient
and necessary condition of robust stability is presented. Both of these
conditions can be checked by solving sets of linear matrix inequalities. Two
numerical examples are presented to confirm the proposed conditions.
