Code stops after first iteration
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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
8 个评论
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
2018-9-3
dpb
2018-9-3
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
2018-9-3
This is the flowchart of my code.
Asha Shibu
2018-9-3
Kevin Chng
2018-9-4
编辑：Kevin Chng
2018-9-4
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
2018-9-4
It is recommended to avoid i and j as loop indices, as these are used for the imaginary unit:
It is much clearer and less buggy to use ii and jj:
for ii = 1:n
...
for jj = 1:n
...
end
end
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2018-9-3
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