# using cumsum for a vector

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C.G.2021-8-18

I have a variable GT2, which is a 1x900 double.
I am trying to do a cumulative sum, where for each cell it does a cumulative sum up to that point, dives this by how many numbers has been summed, and then take the square root.
The current code I have for this is below. When I run this code, it creates a 900x900 double. All I want it to do is do that calculation for each cell so I end up with the same number of values (900) as in GT2. Can anybody help?
flucc = sqrt(cumsum(GT2)./time);

### 回答（1 个）

Cris LaPierre 2021-8-18
Check your dimensaion. Your cumsum will be a 1xn vector. I suspect time must be an nx1. When you perform the division, implicit expansion will turn this into an nxn. The fix would be to transpose time.
% (1xn)./(1xn) = (1xn)
a = cumsum(1:4)./ones(1,4)
a = 1×4
1 3 6 10
% (1xn)./(nx1) = (nxn)
b = cumsum(1:4)./ones(4,1)
b = 4×4
1 3 6 10 1 3 6 10 1 3 6 10 1 3 6 10

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