Parfor+for+if+if How to calculate variable form last if

See my code

parfor i = 1:n
    for j=1:m
        if some_condition(i)
            if some_condition(i)
                t=do_something(i);
                b = [b;t];
            end
        end
    end...
end

I want all b values to get out from the par

Answer 1

[Walter Roberson]

b = [];
parfor i = 1:n
    bt = [];
    for j=1:m
        if some_condition(i)
            if some_condition(i)
                t=do_something(i);
                bt = [bt;t];
            end
        end
    end...
    b = [b, bt];
end

[Karl]

Doesn't this rely on bt having the same size at each iteration?

[Walter Roberson]

No, https://www.mathworks.com/help/parallel-computing/reduction-variable.html does not place that restriction on using appending for reduction variables.

[Karl]

But if I substitute for some_condition and do_something in your code, and define the numbers of iterations, I get the error below. Any idea what's causing this?

m = 7;
n = 3;
b = [];
parfor i = 1:n
    bt = [];
    for j=1:m
        if rand > 0.5
            if rand > 0.5
                t=i;
                bt = [bt;t];
            end
        end
    end
    b = [b, bt];
end

Dimensions of arrays being concatenated are not consistent.

[Walter Roberson]

m = 7;
n = 3;
b = [];
parfor i = 1:n
    bt = [];
    for j=1:m
        if rand > 0.5
            if rand > 0.5
                t=i;
                bt = [bt;t];
            end
        end
    end
    b = [b; bt];
end

b

b = 7x1

1 1 2 2 3 3 3

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[Karl]

Ah, it needed to be [b; bt] rather than [b, bt]. Thanks!