On Determining of LTI Systems Having Nondecreasing Step Response

This brief mainly focuses on discussing computational method of determining whether step responses are nondecreasing for linear time invariant (LTI) systems, including negative real pole systems and complex pole systems. A modified theorem of Jayasuriya and Dharne and a useful fact are offered to deal with negative real pole systems which may have right half plane (RHP) zeros. A necessary condition is presented for complex pole systems to have non-decreasing step responses. Besides, an approximated method is further given as an improvement for determining step responses of complex pole systems.