From help-octave-request at bevo dot che dot wisc dot edu  Tue Jan 23 19:07:05 2001
Subject: Re: RREF (row reduce echelon form)
From: Francesco Potorti` <pot at gnu dot org>
To: "J. R. Miller" <millerjr at u dot washington dot edu>
CC: help-octave at bevo dot che dot wisc dot edu
Date: Wed, 24 Jan 2001 02:06:24 +0100

   I seem to recall several years ago there was an octave command or function
   "RREF" (row reduce echelon form), for whatever version of Octave
   corresponded to Debian 1.2 or 1.3.  Returning, I can't find "RREF".  If
   I'm just not seeing it, please tell me where to look, or how to setup.
   
   If it's not part of Octave, is there somewhere fellow users share this
   kind of code, so I don't have to reinvent the wheel?

I have a couple in my octave mail archive.  Here is one:

 Date: Tue, 16 May 2000 08:46:52 +0200 (SAST)
 From: Dirk Laurie <dirk at calvyn dot puk dot ac dot za>
 Subject: Re: Matlab rref equivalent?
 In-reply-to: <Pine dot LNX dot 4 dot 10 dot 10005151841100 dot 8509-100000 at sentinel dot isdn dot sun dot ac dot za>
  from <Stéfan van der Walt at May>
 To: trax at the-force dot za dot org (Stéfan van der Walt)
 Cc: help-octave at bevo dot che dot wisc dot edu

 [...]
 function [R,k]=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



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