You're trying to write the results of your PARFOR loop into 'B'. The rules for doing this mean that you can only index 'B' with the loop variable 'i', and other constant expressions. For example, the following is valid:
parfor i = 1:10
B(i, 7) = 2 * i;
end
but the following is not:
parfor i = 1:10
B(2 * i:(2 * i + 1)) = i;
end
You need to simplify your expression so that your calculation results in values you can store in this form. Usually it's best in this sort of situation to try and calculate a whole row or column, something like
B = zeros(10, 10);
parfor i = 1:10
B(:, i) = rand(10, 1) * i;
end
and then reshape 'B' after the loop.
