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Gaussian Elimination with Partial Pivoting, how do I swap rows

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Susanna Westersund
Susanna Westersund 2020-10-26
评论： WAGDI AL-BAADANI 2021-3-26
function output= pivGauss(A)
%% Problem Setup
% Get the size of the problem (number of equations / unknowns)
i=1;
[n,~]=size(A);
% Get the coefficient matrix and the RHS vector
C=A(1:n,1:n);
rhs=(1:n,1:n+1);
%% Forward Elimination w/ Partial Piviting
% for each FE iteration:
% 1) find the rows to switch (hint: find the right commands to use from ML3 Tutorial slides)
% 2) switch the rows (hint: you can create a temp variable to hold one set of the values as an intermediate step)
% 3) perform elimination of unknown variables (reminder: use nested loops and MATLAB vector/matrix operations to replace unnecessary loops)
P=(1:n); %pivoting vector
[m,I]=max(abs(A(k:n,k))
for i=1:n-1
piv=i; %selecting the pivot
for j=(i+1):n
if abs(A(j,i))>abs(A(i,i))
U=A(i,:);
A(i,:)=A(j,:);
A(j,:)=U;
end
end
for j=i+1:n
x=A(j,i)/A(i,i);
for k=i+1:n+1
A(j,k)=A(j,k)-x*A(i,k);
end
end
fprintf('\n\nIteration #%2d:\n', i)
fprintf(' The row that is to be switched is %.4e\n', U)
fprintf(' The coefficient matrix is ', A)
fprintf(' The right-hand side vector is ', x)
end
%% Back Substitution
% Use Question 4 in C17_InClass as a reference
% This code has unnecessary loops that can be replaced by MATLAB vector/matrix operations though.
x(n)=Z(n)/U(n,n);
for i=n-1:-1:1
sum=Z(i);
for j=i+1:1:n
sum=sum-U(i,j)*x(j);
end
x(i)=sum/U(i,i);
end
%% Final Display and Output
output=[U, x]
disp(output)
end
  1 个评论
WAGDI AL-BAADANI
WAGDI AL-BAADANI 2021-3-26
function output= pivGauss(A)
↑
Error: Function definition not supported in this context. Create functions in code file.

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回答（1 个）

Pratyush Roy
Pratyush Roy 2020-11-12
Hi Susanna,
The variable 'k' seems to be not defined for the line given below:
[m,I]=max(abs(A(k:n,k))
Can you furnish some more information regarding the variable k?
Regards,
Pratyush

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