how to make a matrix grow inside a parfor loop?

Hi, i would like to do this in a parfor loop:

 S=[];
for n=in:fin
    [s,trueorfalse]=somefunction(someinput);
    if trueorfalse
       S=[S;s];
    end
end

I cannot preallocate because i don't know how much big S will be. I tried some thing but nothing worked so far.

Hope you could help me.

Answer 1

[Edric Ellis]

You should be able to do this. For example, the following works correctly:

S = [];
parfor idx = 1:10
    r = rand();
    if r > 0.5
        S = [S, r];
    end
end

[kira]

that is exactly what i tried, but i get an error, about the way S is used.

[Edric Ellis]

Did you try precisely that code? That code works correctly all the way back even to MATLAB R2008a. Which version did you try it in?

[kira]

hi, i tried my original code again, changing for by parfor an now it works... ?_?

thanks to all for your help...

Answer 2

[Brian B]

You could make S a cell array in the loop, then create a matrix afterward:

somefunction = @(x)deal(x,rand(1)<0.3);
S=cell(100,1);
parfor n=1:100
    [s,trueorfalse]=feval(somefunction, n);
    if trueorfalse
       %S=[S;s];
       S{n} = s;
    end
end
S = cell2mat(S);

[kira]

i could this with S=sparse(fin,dim), but variable fin is very big (O(2^m))