From help-octave-request at bevo dot che dot wisc dot edu  Tue Jan 19 08:11:18 1999
Subject: Re: Row Reduced Eschelon Form?
From: Dirk Laurie <dirk at calvyn dot puk dot ac dot za>
To: sk8mini at ccs dot neu dot edu (Bryan May)
Cc: help-octave at bevo dot che dot wisc dot edu
Date: Tue, 19 Jan 1999 16:16:13 +0200 (SAT)

Bryan May wrote:
> 
> Is there a version of matlab's rref() for octave.  I looked throught the
> linear algebra documentation and couldn't find anything on it.  Any ideas?
> 
The equivalent is quite easy to write as an m-file.  

function R=rref(A,tol)
% reduced row echelon form 
[m,n]=size(A); p=max(m,n);
if nargin<2, tol=p*eps*norm(A,inf); end
  % pad matrix with zeros to make it square
if m~=n, A(p,p)=0; end
[L,U,P]=lu(A);
k=find(abs(diag(U))>tol);
R=U(k,k)\U(k,:);
  % remove added columns if any, add correct number of zero rows
if n<p, R(:,n+1:p)=[]; end
if length(k)<m, R(m,n)=0; end
endfunction

Dirk