Partial pivoting problem in matrix

4 views (last 30 days)
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

Accepted Answer

Pranjal Kaura
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!

More Answers (0)

Tags

Products


Release

R2019b

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!