How to sum part of a matrix using loop command

I have matrix A dimension 35x1435 and I want to get matrix B dimension 35x35 that would have in cell 1,1 a sum of 1 row elements of coulumns 1+36+71+106+..+1401. (so distance is 35 ) and then this matrix B 1,2 cell entry would be a sum of first row elements of columns 2+37+72+107+..+1402 and the cell 1,3 of matrix B would be a sum of columns 3+38+ 73+..+1403 and the same logic for the whole B matrix (so entry 2,1 would be again a sum of 2 row elements 1+36+71+..1401 and the entry of 3,1 would sum the elements in row 3 of coulumns 1+36+71+..+1401)

I tried this loop but it is NOT giving me the correct 35x35 matrix:

for k1 = 1:35

for k2 = 1:35

B(k1,k2) = sum(A(k1,k2:3:end),2);

end;

end;

I followed the 'logic' of this example because here it worked correctly:

M = [4 3 6 8 1 10 5 2 9

1 10 3 9 4 2 5 7 6

9 5 1 7 8 10 3 4 2];

for k1 = 1:3

for k2 = 1:3

S(k1,k2) = sum(M(k1,k2:3:end),2);

end;

end;

Answer 1

[Alan Stevens]

Try replacing

B(k1,k2) = sum(A(k1,k2:3:end),2);

by

B(k1,k2) = sum(A(k1,k2:35:end),2);

[NINA BAJEC]

THANK YOU SO MUCH, now it is correct!