I am new to use parfor, I have searched for the condition but I still can't understand what to do in order to make it work.

I have a code like this...

Copt = cell(65,65);
parfor ws = 1:size(wsv,1)
  t=wsv(ws,1);
  u=wsv(ws,2);
  ...
  ...
  Copt{t,u} = -2;
  ...
  ...
  ...
  C = corr2(F1,F2);
  if (C > Copt{t,u})                     %C returns correlation coef.% 
      Copt{t,u} = C;
  end
end

"Error: The variable in a parfor cannot be classified." displays on the command window when I run my code.

I don't know what to do, is there anyone can give me suggestion?

Answer 1

[Edric Ellis]

To run a PARFOR loop, all variables that you wish to produce as results from the loop must either be sliced or reductions. A sliced variable is one where each iteration of the loop fills out a "slice" which is a subset of the array based on the loop variable. In your case, because you are not indexing "Copt" with the loop index "ws", it cannot be sliced, and so MATLAB cannot work out if your loop is safe to run in parallel.

There's more about variable types in PARFOR here: http://www.mathworks.co.uk/help/distcomp/advanced-topics.html#bq_of7_-1

[Wing Tim Man]

Thanks a lot. I make another cell to contain the value first, say , Copta{wv} = C; so that it can be sliced. After the parfor loop, I use another for loop to write the value back,i.e. for i = 1:size(wsv,1) Copt{wsv(i,1),wsv(i,2)} = Copta{i}; end

And it works !