how to connect different classes?

Dear all, Suppose I have the following function

 function varargout=myfunc(f,varargin)
  atmp=cell(500,4);
  iter=0;
  nf=numel(f);
  fval=nan(nf,1);
  for ii=1:nf
      fval(ii)=f{ii}(varargin{:});
  end
     function c=plus_(a,b)
        id=find(strcmp(atmp(:,1),'+') && [atmp{:,2}]==a && [atmp{:,3}]==b);
        if isempty(id)
           c=a+b;
           iter=iter+1;
           atmp(iter,:)={'+',a,b,c};
        else
           c=atmp{id,end};
        end
     end
 end

This function would not work, but it serves to illustrate the question I would like to ask. The point with this function is that it has a nested function "plus_" and the variables created in the main function (atmp, iter, etc.) are also available to the nested function and the nested function can modify those variables.

In this simple example, "f" is just an array of function handles, e.g. f{1}=@(x,y)exp(x+2*y); the nested function merely adds a and b, but does the actual calculation if a+b has not been computed before. If a+b has been computed before, then the result is just fetched.

For this to work, it should be written in classes overloading operations +, -, *, /, etc. But then how to implement variables atmp and iter such that they are available to the various methods? One solution would be to define atmp and iter as global variables to each of the overloaded methods and initialize it outside the class. A better solution, perhaps, would use handles, notify, events, addlistener, etc. but I do not know how to implement them. Any ideas?

Thanks, P.

[per isakson]

Did you read

• Use nested functions to memoize costly functions, Posted by Loren Shure, February 8, 2006
• http://www.mathworks.com/matlabcentral/answers/31504#answer_40007

[Patrick Mboma]

Hi Per,

I have read the links you suggested, thank you for that. However, I do not see (yet) an obvious way to extend those ideas to classes and objects.

[per isakson]

Search for "Memoization"

• What is memoization and how can I use it in Python? &nbsp - ought to be relevant to Matlab
• http://www.mathworks.se/matlabcentral/fileexchange/index?utf8=%E2%9C%93&term=Memoization

[Patrick Mboma]

Per,

Thanks again for the links. I will look into them although I don't feel like learning python just yet.

[Adam]

I'm confused what the question is here. Your title and the actual part of your post with a ? talks about classes yet everything else seems to be related to nested functions.

If you have a class that overloads the + operator and any other operators then properties of the class are available to the overloaded operators in the nature of being a class.

Answer 1

[Aurele Turnes]

Like per isakson pointed out, I think that you can achieve this by using memoization techniques. The following page on MATLAB Central gives a pretty good example of how to do this:

http://blogs.mathworks.com/loren/2006/02/08/use-nested-functions-to-memoize-costly-functions/

In order to keep the same types of variable that you are using, your function could look something like this:

function f = memoize()
%one-arg F, inputs testable with ==
%allow nonscalar input.

atmp = cell(500,4);
iter = 0;
f = @inner;

      function out = inner(a,b,F)
          % find which in's already computed in x
          if iter>0
              ind= strcmp(atmp(1:iter,1),'+') & (cell2mat(atmp(1:iter,2))==a) & (cell2mat(atmp(1:iter,3))==b);  
              if any(ind)
                  out = atmp{ind,4};
              else
                  out = eval(['a' F 'b']);
                  iter = iter+1;
                  atmp(iter,:) = {F, a , b, out};
              end
          else
              iter = iter+1;
              out = eval(['a' F 'b']);
              atmp(iter,:) = {F, a , b, out};
          end
      end

end

You can then call it and use it as follows:

f = memoize
f(3,4,'+')
f(3,5,'+')
f(3,4,'+')
f(3,4,'*')

Look at the example function memoize2 in the link above to vectorize this technique.

[Patrick Mboma]

Dear Aurele, I think I fairly well understand the concept of memoization and I use it in other applications. But for this one, my problem remains and comes from the fact that the various inputs are objects of a certain class which overloads the operations +, -, *, /, ^, cos, log, exp, etc.

Thanks