MATLAB: How to get sum of elements of lower right triangular matrix.? i have tried this one, can anyone please correct this one

Question

function [sum] = halfsum( a )

[m, n]=size(a); sum=0;

for i= m:-1:1

    for j=n:-1:1
        if i==j || j<=i
            sum=sum+a(i,j);
        end
    end
end
end

output: halfsum([1 2 3;4 5 6;7 8 9])

ans =

    34

Answer 1

out = sum(a(rot90(tril(ones(size(a))),1)>0));