To change 12x12 matrix to 6X12

How can i add a loop to add the 1st two rows of a matrix and then 3rd and 4th row of a matrix and so on till the addition of 11th and 12th row so as to get a 6x12 matrix instead of 12x12 matrix.

for example:

r= 1 2 3 4

5 6 7 8

9 0 1 2

3 4 5 6]

that is 4x4 matrix.

answer= 6 8 10 12

12 4 6 8

converted to 2x4 matrix.

so similar manner how to convert 12x12 matrix to 6x12 matrix using any loop or normal command.

[madhan ravi]

When you ask a question provide an example , don't edit the question after someone answers.

Answer 1

[madhan ravi]

Answer = reshape(r(1:2:end)+r(2:2:end),[],size(r,2))

Answer 2

[Guillaume]

No need for a loop:

m = randi([0 100], 12)  %demo matrix

newm = permute(sum(reshape(m.', size(m, 2), 2, []), 2), [3 1 2])

Basically,

• transpose the matrix (since matlab is organised by columns, not by rows, so a MxN matrix is now a NxM matrix
• reshape so that the pairs of rows to sum are now in columns of 2, so an original MxN matrix is now a Nx2x(M/2) matrix
• sum along the columns, so the orignal MxN matrix is now a Nx1x(M/2) matrix
• and permute back to the original format: Nx1x(M/2) -> (M/2)xN