MATLAB: In the heck does this code work

matrix manipulation

Why in the heck does this code work? It's just a cody problem for a checer board matrix. I figured it out with intuition, trial and error and dumb luck. Lucky too it didn't take too long. I understand the simple use of the colon operator when creating arrays but what happens when using the colon operator with iterations through matrix coordinates? What's going on under the hood hear?
function a = checboard(n)
a=zeros(n);
a(1:2:n,1:2:n)=1;
a(2:2:n,2:2:n)=1;
end

Best Answer

  • Just look at it one bit at a time. The first time, you take an array of zeros and then set every other row and every other column element to 1.
    n = 8;
    a = zeros(n);
    a(1:2:n,1:2:n) = 1;
    Look at a, every other column and every other row are all zeros.
    Look at a as an image:
    imagesc(a);
    Now the next line:
    a(2:2:n,2:2:n) = 1;
    Adds a one staring in the 2nd column and 2nd row. It then jumps every other column and the same with the rows (putting in a 1).
    Now look at a with the bone colormap.
    imagesc(a); colormap(bone)