Change the Number of Inputs

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This example shows how to set the number of inputs for a System object™ with and without using getNumInputsImpl.

If you have a variable number of inputs or outputs and you intend to use the System object in Simulink®, you must include the getNumInputsImpl or getNumOutputsImpl method in your class definition.

These examples show modifications for the number of inputs. If you want to change the number of outputs, the same principles apply.

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 are never called directly.

Allow up to Three Inputs

This example shows how to write a System object that allows the number of inputs to vary.

Update the stepImpl method to accept up to three inputs by adding code to handle one, two, or three inputs. If you are only using this System object in MATLAB, getNumInputsImpl and getNumOutputsImpl are not required.

Full Class Definition

classdef AddTogether < matlab.System
    % Add inputs together
    
    methods (Access = protected)
        function y = stepImpl(~,x1,x2,x3)
            switch nargin
                case 2
                    y = x1;
                case 3
                    y = x1 + x2;
                case 4
                    y = x1 + x2 + x3;
                otherwise
                    y = [];
            end  
        end
    end
end

Run this System object with one, two, and three inputs.

addObj = AddTogether;
addObj(2)

ans =

     2


addObj(2,3)

ans =

     5


addObj(2,3,4)

ans =

     9

Control the Number of Inputs and Outputs with a Property

This example shows how to write a System object that allows changes to the number of inputs and outputs before running the object. Use this method when your System object will be included in Simulink:

  • Add a nontunable property NumInputs to control the number of inputs.

  • Implement the associated getNumInputsImpl method to specify the number of inputs.

Full Class Definition

classdef AddTogether2 < matlab.System
    % Add inputs together.  The number of inputs is controlled by the
    % nontunable property |NumInputs|.
    
    properties (Nontunable)
        NumInputs = 3;   % Default value
    end
    methods (Access = protected)
        function y = stepImpl(obj,x1,x2,x3)
            switch obj.NumInputs
                case 1
                    y = x1;
                case 2
                    y = x1 + x2;
                case 3
                    y = x1 + x2 + x3;
                otherwise
                    y = [];
            end  
        end
        function validatePropertiesImpl(obj)
            if ((obj.NumInputs < 1) ||...
                    (obj.NumInputs > 3))
                error("Only 1, 2, or 3 inputs allowed.");
            end
        end
        
        function numIn = getNumInputsImpl(obj)
            numIn = obj.NumInputs;
        end
    end
end

Run this System object with one, two, and three inputs.

addObj = AddTogether2;
addObj.NumInputs = 1;
addObj(2)

ans =

     2


release(addObj);
addObj.NumInputs = 2;
addObj(2,3)

ans =

     5


release(addObj);
addObj.NumInputs = 3;
addObj(2,3,4)

ans =

     9

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