Use Update and Output for Nondirect Feedthrough - MATLAB & Simulink (original) (raw)

Implement nondirect feedthrough for a System object™ by using the updateImpl, outputImpl, and isInputDirectFeedthroughImpl methods. In nondirect feedthrough, the outputs depend only on the internal states and properties of the object, rather than the input at that instant in time. You use these methods to separate the output calculation from the state updates of a System object. Implementing these two methods overrides thestepImpl method. These methods enable you to use the object in a feedback loop and prevent algebraic loops.

Subclass from the matlab.System Class

To use the updateImpl, outputImpl, andisInputDirectFeedthroughImpl methods, you must subclass from the matlab.System.

classdef IntegerDelaySysObj < matlab.System

Implement Updates to the Object

Implement an updateImpl method to update the object with previous inputs.

methods (Access = protected) function updateImpl(obj,u) obj.PreviousInput = [u obj.PreviousInput(1:end-1)]; end end

Implement Outputs from Object

Implement an outputImpl method to output the previous, not the current input.

methods (Access = protected) function [y] = outputImpl(obj,~) y = obj.PreviousInput(end); end end

Implement Whether Input Is Direct Feedthrough

Implement an isInputDirectFeedthroughImpl method to indicate that the input is nondirect feedthrough.

methods (Access = protected) function flag = isInputDirectFeedthroughImpl(,) flag = false; end end

Complete Class Definition File with Update and Output

classdef intDelaySysObj < matlab.System % intDelaySysObj Delay input by specified number of samples.

properties InitialOutput = 0; end properties (Nontunable) NumDelays = 1; end properties (DiscreteState) PreviousInput; end

methods (Access = protected) function validatePropertiesImpl(obj) if ((numel(obj.NumDelays)>1) || (obj.NumDelays <= 0)) error('Number of delays must be > 0 scalar value.'); end if (numel(obj.InitialOutput)>1) error('Initial Output must be scalar value.'); end end

  function setupImpl(obj)
     obj.PreviousInput = ones(1,obj.NumDelays)*obj.InitialOutput;
  end
  
  function resetImpl(obj)
     obj.PreviousInput = ones(1,obj.NumDelays)*obj.InitialOutput;
  end
  
  function [y] = outputImpl(obj,~)
     y = obj.PreviousInput(end);
  end
  function updateImpl(obj, u)
     obj.PreviousInput = [u obj.PreviousInput(1:end-1)]; 
  end
  function flag = isInputDirectFeedthroughImpl(~,~)
     flag = false;
  end

end end

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