Passing Transforming function to step method of matlab.system.System

Goal: Apply the transform object T to the input data x, in a specefic manner as class A states.

Description: I have a class which does a specefic analyis called T, and another class which want to deploy an object from T on the data, x, in a specific order (class A). A is inherited from matlab.system.System because I can develop my code easier using "step Method" and blah blah. Step method just takes variables and fi objects but not function_handle or a external object (btw why? is it possible in general?). So I import the T object to the A.Func property and pass it to step method. In step method I call the A.Func.do to perform my desired T analysis. I couldn't find any other way :( (I'm newbie). But i constantly get a weird error which I don't understand.

Analysis class T:

 classdef T < handle

    properties
        N
    end

    methods

        % CONSTRUCTOR:
        function obj = T(n)
            if nargin == 1
                obj.N = n;
            else
                obj.N = 16;
            end
        end

        function y = do(x)
            y = abs(fft(x,obj.N));
        end

    end

 end

Structering Class A:

   classdef A < matlab.system.System

  properties

          W           % numeric properties
          Func        % function handle or object
      end

      methods
          % constructor
          function obj = A(Func,w)
              if nargin == 2
                  obj.W = w;
                  obj.Func = Func;
              else % you can use default assining in the properties instead...
                  obj.W = 16;
                  obj.Func = @(x) sin(x);
              end
          end

      end 

      methods (Access=protected)

          function y = stepImpl(obj,x)
              y = obj.Func.do(x)*obj.W;
          end

          function numIn = getNumInputsImpl(~)
              numIn = 1;
          end
      end   
   end

and the main script is:

clear all
clc
x = linspace(0,10*pi,100);
a = T(100);
b = A(T,3);
step(b,x)

but I get this error:

Error using T/do
Too many input arguments.

Error in A/stepImpl (line 30)
            y = obj.Func.do(x)*obj.W;

Error in Main (line 9)
step(b,x)

Class T Code:

http://pastebin.com/KhbsDAQy

Class A Code:

http://pastebin.com/RTiKf6Pz

Answer 1

[Sadid]

Hi, Marry Christmass,

The problem was solved by a technique called object composition. Just for documenting, in the case of static method "." operator should be used. and with the superclass "@" operator. (and bunch of concepts about superiority/inferiority) ... however using direct call (some sort of overloading) was enough to have a working class:

Class A:

classdef A < matlab.system.System
  
  properties
    W           % numeric properties
    Func        % function handle or object
  end

  methods

    function obj = A(Func,w)
      if nargin == 2
        obj.W = w;
        obj.Func = Func;
      else 
        obj.W = 16;
        obj.Func = @(x) sin(x);
      end
    end
   
  end % method
  
  methods (Access=protected)
    

    function y = stepImpl(obj,x)
      y = do(obj.Func,x)*obj.W;
    end
    
    function numIn = getNumInputsImpl(~)
      numIn = 1;
    end

  end
  
end

Class T:

classdef T < handle

  properties
    N
  end

  methods
    
    function obj = T(n)
      if nargin == 0
        obj.N = 16;
      end
      if nargin == 1
        obj.N = n;
      end
    end

    function y = do(obj,x)
      y = abs(fft(x,obj.N));
    end

  end
  
end % method

Main Script:

clear all
clear classes
clc
x = linspace(0,10*pi,100);
a = T(100);
b = A(T,3);
step(b,x)

[Sadid]

Just for curosity I have problem with this implementation and I can't find the reason, your explanation certainly help, thanks

Cass A:

classdef A < matlab.system.System
  
  properties
    W           % numeric properties
    Func        % function handle or object
  end

  methods
    % constructor
    function obj = A(Func,w)
      if nargin == 2
        obj.W = w;
        obj.Func = Func;
      else 
        obj.W = 16;
        obj.Func = @(x) sin(x);
      end
    end
   
  end % method
  
  methods (Access=protected)
    
    function y = stepImpl(obj,x)
      y = step(obj.Func,x)*obj.W;
    end
    
    function numIn = getNumInputsImpl(~)
      numIn = 1;
    end
  end  
end

Class T:

classdef T < handle & matlab.system.System
  
  
  %%Properties
  properties
    N
  end
  
  %%Methods
  methods
    
    % CONSTRUCTOR:
    function obj = T(n)
      if nargin == 0
        obj.N = 16;
      end
      %             obj = obj@handle(n); % it is not possible, why?
      if nargin == 1
        obj.N = n;
      end
    end
  end
  
  methods (Access = protected)
    function y = stepiml(obj,x)
      y = abs(fft(x,obj.N));
    end
    
    function numIn = getNumInputsImpl(~)
      numIn = 1;
    end
    function numIn = getNumOutputsImpl(~)
      numIn = 1;
    end 
  end
  
end % method

with the just the above main script, I get this error:

Error using T/step
The stepImpl method needs to be defined for System objects that return outputs (getNumOutputs > 0).

Error in A/stepImpl (line 29)
      y = step(obj.Func,x)*obj.W;

Error in Main (line 10)
step(b,x)

I can't understand this error :(. Would someone please describe the reason in this case?

Answer 2

[Wayne King]

Hi, I'm not quite sure what you are trying to do in terms of defining your own System object. I'll give you a very simple example of how to write a System object class file with one property and a step() method.

This System object will be called ExpVarBase, it is designed to take a base value with a default of exp(1) and the step method takes a scalar or vector input and raises the base to each element of the input vector.

   classdef ExpVarBase < matlab.System
      % h = ExpVarBase
      properties (Nontunable)
          Base = exp(1);
      end

     methods 
     function obj = ExpVarBase(varargin)
        setProperties(obj,nargin,varargin{:});
     end
  end
     methods (Access=protected)
     function y = stepImpl(obj, x)
        y = obj.Base.^x;
     end
     end

end

You can use this file like this.

      H = ExpVarBase; % use default base
      input = 1i*linspace(0,4*pi,2000);
      y = step(H,input);
      xval = input./1i;
      plot(xval,real(y),xval,imag(y));

Or

    H = ExpVarBase('Base',2);
    y = step(H,2); % same as 2^2

[Sadid]

Thank you Wayne,

I have to perform complicated analysis on the data and not a simple function which can be easily manged by "function_handle". So I like to pass my available T class (which perform pretty complicated task)to A for being applied on x. So passing object from class T to the class A is crucial. I hope I've shown my point.