Issues with my jacobian method code

Question

Kathy Lindquist 2016-10-9

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/306426-issues-with-my-jacobian-method-code

编辑： Marc Jakobi 2016-10-9

I've been messing around with my code for a while, but the x value it outputs never comes out correct.

function [x] = jacobi(A,b,x0,n_iter)
%A=[10 -1 2 0;-1 11 -1 3;0 3 -1 8; 2 -1 10 -1];
%x0=[1;1;1;1];
%b=[6 25 -11 15];
%n_iter=10;
n=length(x0);
x=zeros(size(x0));
for k=1:1:n_iter
      for i=1:1:n
          temp=0;
          for j=1:1:n
             temp=temp+A(i,j)*x(j); 
          end
          temp=temp-A(i,i)*x0(i);
          x(i)=(1/A(i,i))*(b(i)-temp);
      end
      x0=x;
  end
  disp(x)

I'm just unsure which line I have messed up.

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Answer 1

Marc Jakobi 2016-10-9

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https://ww2.mathworks.cn/matlabcentral/answers/306426-issues-with-my-jacobian-method-code#answer_238214

编辑：Marc Jakobi 2016-10-9

在 MATLAB Online 中打开

Just a small error in your code. Here's the correction:

 function [x] = jacobi(A,b,x0,n_iter)
n=length(x0);
 x = zeros(size(x0)); 
for k=1:n_iter
      for i=1:n
          temp=0;
          for j=1:n
              temp=temp+A(i,j)*x0(j); %you should use x0(j) here, not x(j)
          end
          temp=temp-A(i,i)*x0(i);
          x(i)=(1/A(i,i))*(b(i)-temp);
      end
      x0=x;
end
  disp(x)
end

However, you could also do it like this:

function [x] = jacobi(A,b,x0,n_iter)
n=length(x0);
 x = zeros(size(x0)); 
for k=1:n_iter
      for i=1:n
          temp=0;
          inds = [1:i-1, i+1:n];
          temp = A(i,inds)*x0(inds);
          x(i)=(1/A(i,i))*(b(i)-temp);
      end
      x0=x;
end
  disp(x)
end