Class: matlab.System
Package: matlab

Initialize System object




setupImpl(obj) sets up a System object™ and implements one-time tasks that do not depend on any inputs to its stepImpl method. You typically use setupImpl to set private properties so they do not need to be calculated each time stepImpl method is called. To acquire resources for a System object, you must use setupImpl instead of a constructor.

setupImpl executes the first time the step method is called on an object after that object has been created. It also executes the next time step is called after an object has been released.

setupImpl(obj,input1,input2,...) sets up a System object using one or more of the stepImpl input specifications. The number and order of inputs must match the number and order of inputs defined in the stepImpl method. You pass the inputs into setupImpl to use the specifications, such as size and data types in the one-time calculations.

setupImpl is called by the setup method, which is done automatically as the first subtask of the step method on an unlocked System object.

    Note:   You can omit this method from your class definition file if your System object does not require any setup tasks.

    You must set Access = protected for this method.

    Do not use setupImpl to initialize or reset states. For states, use the resetImpl method.

    You cannot modify any tunable properties in this method if its System object will be used in the Simulink® MATLAB System block.


To validate properties or inputs use the validatePropertiesImpl, validateInputsImpl, or setProperties methods. Do not include validation in setupImpl.

Do not use the setupImpl method to set up input values.

Input Arguments


System object handle


Inputs to the stepImpl method


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Setup a File for Writing

This example shows how to open a file for writing using the setupImpl method in your class definition file.

methods (Access = protected)
   function setupImpl(obj)
      obj.pFileID = fopen(obj.Filename,'wb');
      if obj.pFileID < 0
         error('Opening the file failed');

Initialize Properties Based on Step Inputs

This example shows how to use setupImpl to specify that step initialize the properties of an input. In this case, calls to the object's step method, which include input u, initialize the object states in a matrix of size u.

methods (Access = protected)
   function setupImpl(obj, u) 
    obj.State = zeros(size(u),'like', u); 
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