Change Number of Inputs or Outputs

This example shows how to specify two inputs and two outputs to a System object™.

If you specify the inputs and outputs to the stepImpl method, you do not need to specify the getNumInputsImpl and getNumOutputsImpl methods. If you have a variable number of inputs or outputs (using varargin or varargout) and you intend to use the System object in Simulink^®, you must include the getNumInputsImpl or getNumOutputsImpl method in your class definition file.

As with all System object Impl methods, you always set the getNumInputsImpl and getNumOutputsImpl method's access to protected because they are internal methods that users do not directly call or run.

Allow Two Inputs and Two Outputs
Allow Two or Three Inputs and Outputs
Allow Variable Number of Inputs and Outputs

Allow Two Inputs and Two Outputs

To update the algorithm to specify two inputs and two outputs, modify the stepImpl method. You do not need to implement associated getNumInputsImpl or getNumOutputsImpl methods.

methods (Access = protected)
   function [y1,y2] = stepImpl(~,x1,x2)
      y1 = x1 + 1;
      y2 = x2 + 1;
   end
end

Allow Two or Three Inputs and Outputs

This example shows how to write a system object that allows changes to the number of inputs and outputs at setup time. To update the System object to accept either two or three inputs and outputs:

Modify stepImpl to use varargin and varargout
Add a nontunable property to control the number of inputs and outputs
Implement the associated getNumInputsImpl and getNumOutputsImpl methods to specify two or three inputs and outputs.

% This property is nontunable and cannot be changed
% after the after the object has been called
properties (Nontunable)
    numInputsOutputs = 3;   % Default value
end

methods (Access = protected)
   function varargout = stepImpl(obj,varargin)
      varargout{1} = varargin{1}+1;
      varargout{2} = varargin{2}+1;
      if (obj.numInputsOutputs == 3)
         varargout{3} = varargin{3}+1;
      end
   end

   function validatePropertiesImpl(obj)
      if ~((obj.numInputsOutputs == 2) ||...
           (obj.numInputsOutputs == 3))
         error("Only 2 or 3 input and outputs allowed.");
      end
   end

   function numIn = getNumInputsImpl(obj)
      numIn = 3;
      if (obj.numInputsOutputs == 2)
         numIn = 2;
      end
   end

   function numOut = getNumOutputsImpl(obj)
      numOut = 3;
      if (obj.numInputsOutputs == 2)
         numOut = 2;
      end
   end
end

To run this System object with two inputs and two outputs, use this syntax at the command line. Create the object, set the input values for two inputs and two outputs, and then, run the object. Finally, release the object so you can rerun it.

addOne = AddOne;
x1 = 3; 
x2 = 7; 

addOne.numInputsOutputs = 2;
[y1,y2] = addOne(x1,x2);

release(addOne);

Use this syntax to use three inputs and outputs.

x1 = 3; 
x2 = 7; 
x3 = 14; 
addOne.numInputsOutputs = 3;
[y1,y2,y3] = addOne(x1,x2,x3);

Complete Class Definition File with Multiple Inputs and Outputs

Allow Variable Number of Inputs and Outputs

This example shows how to implement a System object whose number of inputs and outputs can change from call to call. To update the algorithm to specify a variable number of inputs and outputs, modify the stepImpl method to include varargin and varargout. In this case, do not implement getNumInputsImpl or getNumOutputsImpl because you do not want to restrict the number of inputs or outputs.

classdef AddOne < matlab.System
    % ADDONE Compute output values one greater than the input values
    
    methods (Access = protected)
        function [varargout] = stepImpl(~,varargin)
            for i=1:nargin-1
                varargout{i} = varargin{i}+1;
            end
        end
    end
end

When you call the System object™, you can use any number of inputs.

obj = AddOne;
a = obj(3)

a =
     4

[a,b,c] = obj(3,6,9)

[a,b] = obj(3,6)

If your System object is used in Simulink, you cannot use a variable number of outputs. You must implement getNumInputsImpl and getNumOutputsImpl to set the exact number of inputs and outputs.

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