Change the Number of Inputs - MATLAB & Simulink (original) (raw)

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)

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:

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)

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

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

See Also

getNumInputsImpl | getNumOutputsImpl

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