How to sum the diagonal numbers and numbers after the diagonal of a matrix

Write a function called halfsum that takes as input a matrix and computes the sum of its elements that are in the diagonal or are to the right of it. The output arguments name is summa.

I have absolutely no idea how to start with this problem. How am I meant to use a for-loop for this?

Thank you very much

[Mohammad Sami]

Look at function diag and triu

Answer 1

[Matt Shellhammer]

total = 0;
for idx = 1:size(a,1)
    total = total + a(idx,idx);
end

or

sum(a(1:(size(a,1)+1):size(a,1)*size(a,2)))

or

sum(diag(a))

and for the indices to the right of it... (assuming its square).

total = 0;
for idx = 1:size(a,2)-1
    total = total + a(idx,idx+1);
end

Answer 2

[Bhaskar R]

function summa = halfsum(inp_mat)
    summa = zeros(2,1);     % first element is sum of diagonal elements, second is sum of diagonal to right
    summa(1) = sum(diag(inp_mat))    %diagnal elemts 
    summa(2) = sum(diag(inp_mat, 1)) % right to diagonal   
end