% indices

format short g; echo on;

% column filling
A = zeros(3,4)
A(:) = [1:12]
pause;

% submatrices
A(1:2:end,:)
ind = find( rem(A,5) == 0)
A(ind) = NaN
pause;

% spreading entries 
B(1:3:7,1:2:7) = A
B(2:3:end,:) = -1
pause;

echo off; format;
