Here's one way without loops (just typing the matrix out):
A=[1 1 1 0 0 0 0 0 0; 1 1 1 1 1 1 0 0 0 ; 1 1 1 1 1 1 1 1 1 ];
But I guess that's not what you're looking for.
Maybe this instead:
N = 3;
A_1 = repelem(cummax(eye(N)),1,N)
isequal(A,A_1) % check
Or this:
A_2 = zeros(N,N^2);
for ii = 1:N
A_2(ii,1:N*ii) = 1;
end
A_2
isequal(A,A_2) % check
