The main function creation in matlab has the following form:
function output = FuncName(input)
output = f(input)
end
Input can be a matrix, and, in your case, the function is to get the corners, which can be done with simple index. So:
function output = FuncName(input)
%Up-Left %Up-right %Bottom-left %Bottom-right
output = [input(1,1), input(1, end); input(end, 1),input(end,end) ];
end
