Matrix of sums of submatrices

[David Barker]

I have matrix A. I'd like to create a new matrix B where each element is the sum of a corresponding 60x60 submatrix of A. By sum I mean the sum of each element of the submatrix. How can I do that?

[Joseph Coveney]

Here's an approach that I would use. I illustrate it with a toy example for brevity's sake.

version 17.0

clear *

mata:

A = 1, 2, 3, 4 \ 5, 6, 7, 8 \ 9, 10, 11, 12 \ 13, 14, 15, 16
A

A[| 1,1\2,2 |]
A[| 1,3\2,4 |]
A[| 3,1\4,2 |]
A[| 3,3\4,4 |]

// Begin here
B = sum(A[| 1,1\2,2 |]), sum(A[| 1,3\2,4 |]) \
    sum(A[| 3,1\4,2 |]), sum(A[| 3,3\4,4 |])
B

end

exit

[David Barker]

Perfect, thank you!