MATLAB: Cumulative sum of some columns of matrix

Question

I have a 100 x 12 matrix of monthly climate data values.

I want to create a matrix with the cumulative sum of the three previous months.

How can I use cumsum() to get the cumulative sum by row of a certain number of specified columns, not the whole row?

Answer 1

You seem to want to do cumsum along the second dimension, so trivial is to use

 res = cumsum(yourMat,2);

but this will produce the typical cumsum. If you want to add every 3 columns only for a specific row,

 yourRow = someval; %within your dimension range
 cs = 1:size(yourMat,2);
 cs1 = [1 1 cs(1:end-2)];
 res = arrayfun(@(x,y) sum(yourMat(yourRow,x:-1:y)), cs, cs1, 'uni',0);