maxX = 20;
maxY = 15;
A=zeros(maxX,maxY);
A(1,:) = 1
A(:,2) = 1
A(4,4) = 1
%the following lines just display the matrix. The details are not important!
imagesc(A');
set(gca,'YDir','normal');
colormap(1-gray);
axis equal;
axis tight;
