Overload operator doesn't work into workers

I overloaded the plus operator for my class, but it doesn't work into parfor loop. The error is the following

Error using + (line 32)
Dot indexing is not supported for variables of this type.

Function is the following

function this = plus(this, offspring)
  this.Individuals(end+1:end+numel(offspring.Individuals)) = offspring.Individuals;
end

Why it doesn't work in the parfor but work correctly in the for loop?

[Andrea Stevanato]

Classes are placed in different files

classdef ClassA < handle   
    properties
      value = []
    end

    methods
        function obj = ClassA(val)
            obj.value = val;
        end
    end
end

classdef ClassB < handle
    properties
      a = [];
    end

    methods
      function obj = ClassB(A)
          obj.a = A;
      end

      function obj = plus(obj, A)
          obj.a(end+1:end+numel(A)) = A;
      end
    end
end

Here the test

>> a = ClassA(10);
>> b = ClassB(a);
>> for i = 1:3
b = b+a;
end
>> parfor i = 1:3
b = b+a;
end

Error:

An UndefinedFunction error was thrown on the workers for 'plus'.  This might be because the file containing 'plus' is not accessible on the workers.  Use addAttachedFiles(pool, files) to specify
the required files to be attached.  See the documentation for 'parallel.Pool/addAttachedFiles' for more details.

Caused by:
    Undefined function 'plus' for input arguments of type 'ClassA'.

Edit: I have already tried to do the following commands without success.

>> addAttachedFiles(gcp(), 'ClassA.m')
>> addAttachedFiles(gcp(), 'ClassB.m')

Answer 1

[Sayyed Ahmad]

class handel is a pointer of Memory. To better understand try this codes

a = ClassA(10);
b = ClassB(a);
a.value
b.a.value
a.value=20
b.a.value

so you Change in each time the value in the same Memory. if you did not useing of handle class your code will work.

[Andrea Stevanato]

I need handle class in my code, but now i don't have anymore this error but other. If i use b = b+a into for loop it's work but if i run b = b+a into parfor loop i get error

Too many input arguments.

the same code, the only change is for with parfor.

Answer 2

[Guillaume]

I don't know the reason for the particular error you get but you will always get an error anyway since your code is not parallelisable. You're growing an array by an arbitrary size at each step of the loop. In a parfor loop all steps of the loop occur at the same time, hence you would be growing the same array in parallel without anyway to reconcile all the grown arrays:

• for loop

    i = 1:
      b.a = [b.a a(1)]

    i = 2:
      b.a = [b.a a(1) a(2)]

    i = 3:
      b.a = [b.a a(1) a(2) a(3)]

• parfor

     i = 1                 i = 2                   i = 3
     b.a = [b.a a(1)]      b.a = [b.a a(2)]        b.a = [b.a a(3)

     put together:  b.a = ????

[Andrea Stevanato]

b.a = [a(index1) a(index2) a(index3)] with arbitrary order. Even if i tried to do it without handle object and i get this error:

>> parfor i = 1:5
c = c+a;
end
Too many input arguments.

The same code works with for loop

Edit: I'm wrong i get the same error with and without handle!

[Guillaume]

with arbitrary order

That may be what you want but that's not the way parfor works. parfor, as designed, is not capable to paralellise your code (with or without handle). You cannot have parallel branches growing the same array at once.

What may work (completely untested, don't have the toolbox):

classdef classB < handle
   properties
      a;
      accum = {};
   end
   methods 
      function this = classB(A, accumsize)
          this.a = A.value;
          this.accum = cell(1, accumsize);
      end
      function add(this, A, idx)
          this.accum{idx} = A.value;
      end
      function result = gather(this)
           result = [this.a, this.accum{:}];
      end
   end
end
a = classA(10);
numadds = 3
b = classB(a, numadds);
parfor i = 1:numadds
   b.add(a, i);
end
b.gather