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

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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:
Class A Code:

Accepted Answer

Sadid
Sadid on 26 Dec 2012
Edited: Sadid on 26 Dec 2012
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)
  1 Comment
Sadid
Sadid on 26 Dec 2012
Edited: Sadid on 26 Dec 2012
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?

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More Answers (1)

Wayne King
Wayne King on 24 Dec 2012
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
  1 Comment
Sadid
Sadid on 24 Dec 2012
Edited: Sadid on 24 Dec 2012
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.

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