Partial pivoting problem in matrix
1 view (last 30 days)
Show older comments
Netanel Malihi
on 4 Dec 2021
Answered: Pranjal Kaura
on 30 Dec 2021
I'm getting a mistake in my matrix when trying to get the max number at the column and swiching rows , I'm pretty sure its got to do with an incorrect index.
Im using the partial pivoting method.
thank you for your help.
clear;
clc;
n=5;
v=repelem(4,n);
A=diag(v);
i=1;
j=1;
A(1,n)=-1
A(n,1)=-1
for i=1:n
for j=1:n
if i==j+1 ||j==i+1
A(i,j)=-1;
end
end
end
b=1:n;
B=b'/n;
A=[A,B]
for k=1:n-1
[max_A1,row_i]=max(abs(A(k:end,k)))
if row_i~=k
A1=A(k,:)
A(k,:)=A(k,:)
A(row_i,:)=A1
else
end
for i=k+1:n
L=A(i,k)/A(k,k)
for j=k:n+1
A(i,j)=A(i,j)-L*A(k,j)
end
end
end
0 Comments
Accepted Answer
Pranjal Kaura
on 30 Dec 2021
Hey,
Please refer the code below
clear;
clc;
n=5;
v=repelem(4,n);
A=diag(v);
i=1;
j=1;
A(1,n)=-1;
A(n,1)=-1;
for i=1:n
for j=1:n
if i==j+1 ||j==i+1
A(i,j)=-1;
end
end
end
b=1:n;
B=b'/n;
A=[A,B];
% test matrices
% A = [25 5 1 106.8;
% 64 8 1 177.2;
% 144 12 1 279.2];
% A = [1 2 -4 3;
% 2 5 -6 10;
% -2 -7 3 -21;
% 2 8 -5 38];
% n = 4;
%partial pivoting code
for k=1:n-1
[max_A1,row_i]=max(abs(A(k:end,k)));
row_i = row_i - 1 + k;
if row_i~=k
A1=A(k,:);
A(k,:)=A(row_i,:);
A(row_i,:) = A1;
end
for i=k+1:n
L=A(i,k)/A(k,k);
A(i, k:end) = A(i, k:end) - A(k, k:end)*L;
% for j=k:n+1
% A(i,j)=A(i,j)-L*A(k,j)
% end
end
end
Hope this helps!
0 Comments
More Answers (0)
See Also
Categories
Find more on Dates and Time in Help Center and File Exchange
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!