# hi am working on a code for gaussian elimination

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Ifechukwu on 22 May 2014
Edited: Walter Roberson on 17 Jul 2016
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
John D'Errico on 22 May 2014
I fixed it for you, but you need to learn how to flag a block of code as such. Otherwise, it is unreadable.

George Papazafeiropoulos on 22 May 2014
Edited: Walter Roberson on 17 Jul 2016
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
Ifechukwu on 22 May 2014
Thanks a lot it helps

Cory Cress on 17 Jul 2016
Edited: Walter Roberson on 17 Jul 2016
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.