.. currentmodule:: control

The classes listed below are used to represent models of input/output systems (both linear time-invariant and nonlinear). They are usually created from factory functions such as :func:`tf` and :func:`ss`, so the user should normally not need to instantiate these directly.

.. autosummary::
   :toctree: generated/
   :template: custom-class-template.rst

   StateSpace
   TransferFunction
   InputOutputSystem
   FrequencyResponseData
   TimeResponseData

The following figure illustrates the relationship between the classes and some of the functions that can be used to convert objects from one class to another:

Input/output systems are accessed primarily via a set of subclasses that allow for linear, nonlinear, and interconnected elements:

.. autosummary::
   :template: custom-class-template.rst
   :nosignatures:

   InputOutputSystem
   InterconnectedSystem
   LinearICSystem
   LinearIOSystem
   NonlinearIOSystem

.. autosummary::
   :template: custom-class-template.rst
   :nosignatures:

   DescribingFunctionNonlinearity
   flatsys.BasisFamily
   flatsys.FlatSystem
   flatsys.LinearFlatSystem
   flatsys.PolyFamily
   flatsys.SystemTrajectory
   optimal.OptimalControlProblem
   optimal.OptimalControlResult