MATLAB: How to reduce a matrix size in 1 dimension

matrixmatrix manipulationsize;

I would like to reduce the size of a matrix (M,N) in one direction (the rows) by averaging the values of neighboring cells.

So the cells (1,1), (1,2) in the old matrix will be represented by their average in (1,1) in the new matrix.

How can I do this?

Best Answer

Assuming that N is even:

reducedm = reshape(mean(reshape(m, M, 2, N/2), 2), M, N/2);

Note that I've averaged every two columns as per you example (:, 1) and (:, 2), which contradict the fact you said in the row direction. Just flip the matrix before and after and swap M for N, if you want rows.

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MATLAB: Multiplying mmN matrix internally

   prod

performs element-wise multiplication.

If you want matrix multiplication, you can use something like :

A = rand(2,2,2);
res = A(:,:,1);
for i = 2:size(A,3)
  res = res*A(:,:,i);
end

MATLAB: How to reduce a matrix size

X = rand(20, 30);
R = reshape(X, 2, 10, 2, 15);
S = sum(sum(R, 1), 3) * 0.25;
Y = reshape(S, 10, 15);

This can be wriiten in one line also. If more speed is needed you can use the faster C-Mex FEX: BlockMean.

Best Answer

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MATLAB: How to reduce a matrix size

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MATLAB: Multiplying mmN matrix internally