Mathematica provides a core set of functions for performing block-diagram reduction and various model manipulations. Building on Mathematica's unique symbolic architecture, models and their connections are elegantly represented and manipulated as symbolic expressions.
SystemsModelSeriesConnect — connects two models in series
SystemsModelParallelConnect — connects two models in parallel
SystemsModelStateFeedbackConnect — connects two models using state feedback
SystemsModelFeedbackConnect — connects two models using feedback
SystemsModelDelete — deletes a subsystem
SystemsModelExtract — extracts a subsystem