Code stops after first iteration

So I have this MATLAB code for LU decomposition with partial pivoting and the code stops after doing one iteration even though I have added a loop. What could possibly be the reason

function[Q,P]=lupivot(A)
%%LU factorization with partial pivoting%%
[i,j]=size(A);
n=length(A);
if i~=j
    disp('The Matrix must be square to proceed further');
end 
P=eye(n); %set permutation matrix to I%
Q=zeros(n);%set Q matrix%
for j=1
Q(:,1)=A(:,1);%initialize the first column to first column of A
[temp,pos] = max(abs(Q(1:n,1)));%Finding the maximum value in the column%
if Q(1,1)==temp %Checking if the diagonal element has maximum value%
  for k=2:n
       Q(1,k)= 1/Q(1,1)*((A(1,k)));
  end
else
Rowswap = pos;
Q([Rowswap, 1],:) = Q([1, Rowswap],:);
A([Rowswap, 1],:) = A([1, Rowswap],:);%Swapping the corresponding rows of Q,P and updating A
P([Rowswap, 1],:) = P([1, Rowswap],:);
  for k=2:n
       Q(1,k)= 1/Q(1,1)*((A(1,k)));
  for k=2:n
        Q(k,2)= A(k,2)-((Q(k,1)*Q(1,2)));
  end
  end
end
end 
for j=2:n
[temp1,pos1] = max(abs(Q(j:n,j)));%Finding the maximum value in the column%
if Q(j,j)==temp1 %Checking if the diagonal element has maximum value%
 for k=j+1:n
       Q(j,k)= 1/Q(j,j)*((A(j,k))-(Q(j,1:j-1)*Q(1:j-1,k)));
    for k=j:n
        Q(k,j)= A(k,j)-(Q(k,1:j-1)*Q(1:j-1,j));
    end
  end
else
rowswap = j-1+pos1;
Q([rowswap, j],:) = Q([j, rowswap],:);
A([rowswap, j],:) = A([j, rowswap],:);%Swapping the corresponding rows of Q,P and updating A
P([rowswap, j],:) = P([j, rowswap],:);
 for k=j+1:n
       Q(j,k)= 1/Q(j,j)*((A(j,k))-(Q(j,1:j-1)*Q(1:j-1,k)));
  for k=j:n
        Q(k,j)= A(k,j)-(Q(k,1:j-1)*Q(1:j-1,j));
 end
 end
 j=j+1;
end
end
end

OUTPUT

>> [Q,P]=lupivot(A)

Q =

     12.0000   -0.6667    0.3333    0.8333
      3.0000  -11.0000   -0.1818   -0.0455
      6.0000    2.0000    0.3636      -Inf
     -6.0000         0    4.0000         0

[jonas]

Is this the loop you have added?

for j=1

Anyway, you should indicate where you have added something and what your expected output is.

[Asha Shibu]

for j=2:n This is my loop

[dpb]

You've got double-nested loops on the same index in

...
for k=j+1:n
  Q(j,k)= 1/Q(j,j)*((A(j,k))-(Q(j,1:j-1)*Q(1:j-1,k)));
  for k=j:n
    Q(k,j)= A(k,j)-(Q(k,1:j-1)*Q(1:j-1,j));
  end
end
...

I've not tried to read the code see if could decipher what might possibly be intended here, but this can't be correct...

[Asha Shibu]

This is the flowchart of my code.

[Asha Shibu]

How can I change the index for double nested loop?

[Kevin Chng]

Hi,

According to dpb, double nested on same index

for k=1:1:n

        for k=1:1:n
        end

 end

%Try change the inner loop index k to other name (j):

for k=1:1:n
     for j=1:1:n
     end
end

[Asha Shibu]

You mean like this?

   for k=j+1:n
         Q(j,k)= 1/Q(j,j)*((A(j,k))-(Q(j,1:j-1)*Q(1:j-1,k)));
    for m=j:n
          Q(m,j)= A(m,j)-(Q(m,1:j-1)*Q(1:j-1,j));
   end

[Stephen23]

It is recommended to avoid i and j as loop indices, as these are used for the imaginary unit:

https://www.mathworks.com/help/matlab/ref/i.html

It is much clearer and less buggy to use ii and jj:

for ii = 1:n
    ...
    for jj = 1:n
        ...
    end
end