  Model order reduction algorithms for large-scale descriptor systems are
proposed using balanced truncation, in which symmetry or block skew symmetry
(reciprocity) and the positive realness of the original transfer matrix are
preserved. Two approaches based on standard and generalized algebraic Riccati
equations are proposed. To accelerate the algorithms, a fast Riccati solver,
RADI (alternating directions implicit [ADI]-type iteration for Riccati
equations), is also introduced. As a result, the proposed methods are general
and efficient as a model order reduction algorithm for descriptor systems
associated with electrical circuit networks.
