A = [1 2 3; 2 20 26; 3 26 70];

L = zeros(length(A));
U = zeros(length(A));

for j = 1: length(A)
    for i = 1:length(A)
        sum = 0;
        p = j-1;
        for k = 1:p
            sum = sum+(L(i,k)*U(k,j));
        end
        if i == j
            U(i,j) = 1;
        end
        if i >= j
            L(i,j) = A(i,j) - sum;
        else
            U(i,j) = (1/L(i,i))*(A(i,j)-sum);
        end
    end
end

A
L
U