Descriptor Systems and Control Theory, Report no. LiTH-ISY-R-2688

This report is a brief survey over different concepts and methods concerning singular systems. Singular system is also called differential algebraic equations (DAE) since a DAE model may involve both differential and algebraic equations. There is an growing interest in DAE systems much depending on the increased usage of object oriented modeling languages, like Modelica, in the modeling of dynamical systems. These programs often give DAE models as result. Another advantage of DAE models is that they sometimes can keep the natural structure of the dynamical model.