MATLAB: Building up a Matrix using for LOOP and summation

for loopMATLABsummation

Hello fellows,
I am trying to make this equation but I couldn't do the summaiton part , i tried to use the double for loop but still not sure how to do the summation part,
I have the matrix " a " already defined 4×4 also initial l and u matrices are defiend l=eye(N),u=zeros(N,N);
any hints?

Best Answer

I believe the below is correct.
I=eye(4);
u=zeros(4);
u(1,1:4)=a(1,1:4);
I(1:4,1)=a(1:4,1);
for i=2:4
    for j=1:4
        u(i,j)=a(i,j)-sum(I(i,1:i-1).*u(1:i-1,j)');
        if i<j
            I(j,i)=(I(j,i)-sum(I(j,1:i-1).*u(1:i-1,i)'))/u(i,i);
        end
    end
end
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