Gauss-Seidel code gives wrong answers

Hello,

I am hoping someone can assist me with this problem. I created a Gauss-Seidel code that will allow me to solve a set of linear equations, finding x1, x2 x3 and x4. I made two matrices; A=[4 -21 -7 1; -4 0 -3 11 ; 4 -1 10 -1; 151/8 5 8 -3] and b =[11; 15; 19; -12;]. Through using the equatio Ax=b i would be able to find the unknows, which worked using the backslash built in solver. But my code below give 4 values for x but they do not match the reuslts of the built in solver and do not equate when substitued back into a line of the linear equations.

A major aspect of the code is that it is meant to make your matrix diagonally dominant to solve.

My code is as follows:

function gauss-seidel
A=input('write matrix a')
b=input('write matrix b')
x=linspace(0,0,length(A))';
n=size(x,1);
normVal=Inf; 
 

nmax=1000; %number of maximum iterations which can be reached%
tol=0.000001; % Tolerence for method%
iter=0; 


while normVal>tol && iter<nmax
    x_old=x;
    [V,A]=eig(A);
    TF=isdiag(A);
  if TF==0    
      fprintf('the matrix is not diagonally dominant')
  else
    for i=1:n
        
        guess=0;
        
        for j=1:i-1
                guess=guess+A(i,j)*x(j);
        end
        
        for j=i+1:n
                guess=guess+A(i,j)*x_old(j);
        end
        
        x(i)=(b(i)+guess)/(A(i,i));
    
  end
    iter=iter+1;
    normVal=norm(x_old-x);
  end
end

fprintf('Solution of the system is : ')
for i=1:length(x)
fprintf(' %1.4f  ',x(i));

end
fprintf('in %d iterations ',iter)

[Mohammad shadab]

Suii

Answer 1

[Prabhan Purwar]

Hi,

Seems duplicate questions are posted by mistake, kindly refer to ans using following link:

https://www.mathworks.com/matlabcentral/answers/518877-gauss-seidel-method-help

Thanks.

[kemgi]

Thank you ?