MATLAB: Cumulative sum that restarts whenever it reaches certain level

conditional sum

Good evening I have a matrix A of 250*3 what i try to do is the following: the first time that the cumsum "of raws" is > 6, i replace the corresponding value in matrix A with zero and restart the cumsum form the value after the zero. then we repeat this once more: the first time the new cumsum >6 we replace it with zero and restart the cum sum we repeat this untill we arrive to the last raw of the matrix
Thank u in advance

Best Answer

rng default
x = randi(3,[20 1]);
thresh = 6;
while 1
    xc = cumsum(x);
    k  = find(xc > thresh,1,'first');
    if isempty(k)
        % done
        break
    end
    x(k) = -xc(k-1);
end
When you say set that row equal to zero, the cumsum on the next row will still be greater than 6. (something greater than 6 + 0 is still greater than 6). Thus you need to set the value to the negative of the previous value in order to reset the cumulative sum. If you need zeros at the end, remove the negatives.
% If you need to zero out those points
x(x<0) = 0
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