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I have a matrix A of size 3780x30974. This matrix consists of 0 and 1. I would like to calculate the sum of fixed windows of length 21 (180 blocks). This should be reiterated, so that the output returns a vector of size 180x30974.

If the first 21 values in a column have a value of 1, the output should return 21. However, if the following 21 values have a value of 1 again, it should return 21 as well. In my code, it accumulates the values, so I obtain 42.

I have t=3780, p=180, w=21;

B = movsum(A,w); % the sum of a moving window with width w

This question is somehow related to a question previously asked, yet with a different problem setting. I thought about a loop to say "perform from t=1:p", yet it didn't work.

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result = permute(sum(reshape(A, w, [], size(A,2)), 1), [2 3 1]);

This works as follows: reshape A into a 3D array of size 21×180×30974:

reshape(A, w, [], size(A,2)), 1)

then sum along the first dimension

sum(..., 1)

and finally remove the first (singleton) dimension by permuting it to the end:

permute(..., [2 3 1])

Note that Matlab arrays have an infinite number of trailing singleton dimensions, so moving a singleton dimension to the end is the same as removing it.

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2 Comments

Solution works perfectly well. To understand your code a little bit better, could you please tell me what part of your explantion does the [2 3 1] play?
@Joe It permutes the first (singleton) dimension to the end, which is the same as removing it. I added an explanation

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