Why is Matlab not abled to run this as a parfor loop?

I want to run a loop like this as a parfor loop. In my eyes it shouldn't matter in which order the different iterations are called. 'a' is only used as reduction variable.

     a = zeros(1,5);
      parfor i= 1:1000
          dts = randi(10)-1;
          if dts == 0 
              a(1) = a(1) + 2;
          elseif dts <= 5
              a(dts) = a(dts) +1;
          end
      end

This is the error, which i get:

Error using Test (line 2) Error: The variable a in a parfor cannot be classified.

See Parallel for Loops in MATLAB, "Overview". Why wouldn't Matlab allow this program? How do i fix it?

Edit: Since the Codeblock-function doesn't seem to work: http://pastebin.com/FUHFe61T

[Sean de Wolski]

That doesn't even work with a regular for-loop. That should always be the first step: making sure it works with a regular loop.

[Matthias]

I had a little typo. It is supposed to be randi(10) not rand(10).

Answer 1

[Friedrich]

Hi,

MATLAB thinks a is a sliced variable and you get troubles with the indices here. I think in such a case its better to use a Reduction Variable like this:

X = zeros(1,5);
parfor i= 1:1000
    a = zeros(1,5);
    dts = randi(10)-1;
    if dts == 0
        a(1) = (a(1) + 2);
    elseif dts <= 5
        a(dts) = a(dts) +1;
    end
    X = X + a;
end

For more information about variable types see here:

http://www.mathworks.com/help/distcomp/advanced-topics.html