The code doesn't create a 2 dimensional array - it is supplied with a 2 dimensional array (argument x) and the function returns the values that are at the corners of that array
function [a,b,c,d]=corners(x)
[y,z]=size(x); %Gets the size of x - values not used in the function so largely serves no purpose
a=x(1,1); %top left value returned
b=x(1,end); %top right value returned
c=x(end,1); %bottom left value returned
d=x(end,end); %bottom right value returned
end
