hi am working on a code for gaussian elimination

Question

Ifechukwu 2014-5-22

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编辑： Walter Roberson 2016-7-17

hi am working on a code for gaussian elimination but I can't get the code to run for non square matrix please what should I do Here is the code and thanks in advance

function [x,U] = gausselim(A,b)
% function to perform gauss eliminination
%FORWARD ELIMINATION
n=length(b);
m=zeros(n,1);
x=zeros(n,1);
for k =1:n-1;
    %compute the kth column of M
    m(k+1:n) = A(k+1:n,k)/A(k,k);
    %compute An=Mn*An-1, bn=Mn*bn-1
    for i=k+1:n;
        A(i, k+1:n) = A(i,k+1:n)-m(i)*A(k,k+1:n);
    end;
    b(k+1:n)=b(k+1:n)-b(k)*m(k+1:n);
end;
U= triu(A);
%BACKWARD ELIMINATION
x(n)=b(n)/A(n,n);
for k =n-1:-1:1;
    b(1:k)=b(1:k)-x(k+1)* U(1:k,k+1);
    x(k)=b(k)/U(k,k);
end;
end

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John D'Errico 2014-5-22

I fixed it for you, but you need to learn how to flag a block of code as such. Otherwise, it is unreadable.

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Answer 1

George Papazafeiropoulos 2014-5-22

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编辑：Walter Roberson 2016-7-17

在 MATLAB Online 中打开

The correct function is:

function [x,U]=gausselim(A,b)
% function to perform gauss eliminination
%FORWARD ELIMINATION
n=length(b);
m=zeros(n,1);
x=zeros(n,1);
for k =1:n-1;
      %compute the kth column of M
      m(k+1:n) = A(k+1:n,k)/A(k,k);
      %compute
      %An=Mn*An-1;
      %bn=Mn*bn-1;
      for i=k+1:n
          A(i, k+1:n) = A(i,k+1:n)-m(i)*A(k,k+1:n);
      end;
      b(k+1:n)=b(k+1:n)-b(k)*m(k+1:n);
end
U= triu(A);
%BACKWARD ELIMINATION
x(n)=b(n)/A(n,n);
for k =n-1:-1:1;
      b(1:k)=b(1:k)-x(k+1)* U(1:k,k+1);
      x(k)=b(k)/U(k,k);
end
end

After this try to run the code:

A=rand(5,4);
b=rand(4,1);
[x,U] = gausselim(A,b)

Is this what you want? I hope this helps...

George

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Ifechukwu 2014-5-22

Thanks a lot it helps

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Answer 2

Cory Cress 2016-7-17

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编辑：Walter Roberson 2016-7-17

在 MATLAB Online 中打开

I think the command you are looking for is rref :

R = rref(A)
[R,jb] = rref(A)
[R,jb] = rref(A,tol)

It produces a matrix in reduced row echelon form. Perhaps your exercise was to write it yourself, but for others that want to use a built-in function use rref.