MATLAB: How to sum n lines of a matrix to another matrix

matrixmatrix to other matrixn linessum of matrices

So basically, i have a matrix Apit with the index of (51*n,5,1000) and what i wanted is another matrix TotalApit, with the index (51,5,1000), that sums up 'n' lines by 'n' lines.
like:
if n = 2, Apit(102,5,1000) and TotalApit(51,5,1000)
TotalApit(1,1,1) = Apit(1,1,1)+Apit(2,1,1)
TotalApit(2,1,1) = Apit(3,1,1)+Apit(4,1,1)
So i want that 1 line of TotalApit correspond the sum of n lines of Apit
Can someone help me?

Best Answer

You could do this:
Apit = rand(102,5,1000);
TotalApit = zeros(51,5,1000);
% Now do the sum
[rows, columns, slices] = size(Apit)
n = 2;
tic
k = 1;
for row = 1 : n : rows-n
  thisVolume = squeeze(Apit(row:(row+n-1), :, :));
  thisSum = sum(thisVolume, 1);
  TotalApit(k, :, :) = thisSum;
  k = k + 1;
end
toc
Takes a hundreth of a second on my computer. You might be able to do it even faster with convn(). And it would be only 1 or 2 lines of code.
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