From help-octave-request at bevo dot che dot wisc dot edu Mon Jan 26 08:44:29 2004 Subject: Re: Understanding how octave works... From: Paul Kienzle To: David Bateman Cc: help-octave at bevo dot che dot wisc dot edu, Joerg Frochte Date: Mon, 26 Jan 2004 09:43:06 -0500 I've found QR decomposition to be successful as well. I haven't compared it to the results of SVD. ## system solution [Q,R,P] = qr(X,0); p = R\(Q'*b); p(P) = p; See wpolyfit.m in octave-forge. The function test_wpolyfit has a number of difficult systems to solve. Paul Kienzle pkienzle at users dot sf dot net On Jan 26, 2004, at 9:27 AM, David Bateman wrote: > If the matrix is square we call the "solve" routine based on an LU > decomposition of the matrix (dgetrf and dgetrs). If LAPACK flags the > result as being doubtful with the info flag then we fall back on > "lssolve" that uses an SVD (dgelss). > > According to Joerg Frochte (on 01/26/04): >> >> The result in octave is quite OK, but the result my own program >> computes >> is very unpleasing. >> >> ans = [ -7.12e+11-3.70e-05-6.03e+13 1.82e-03 1.74e+00-1.70e+15 >> 1.48e-01 >> 2.79e+00 6.10e-02 ] >> >> This has something to do with the fact that A is very close to be >> singular. >> >> octave:21> cond(A) >> ans = 2.9251e+18 >> >> Nevertheless, the result of octave is more pleasing. >> How does octave deal with such a situation? >> I have the source-code but I am unable to find a point to start my >> analysis, >> because I do not know how octave is designed. >> >> Could you tell me how octave works in this situation or give me a >> file and >> line where to start in the octave code? >> >> Thanks very much, >> >> Joerg Frochte >> >> >> >> >> ------------------------------------------------------------- >> Octave is freely available under the terms of the GNU GPL. >> >> Octave's home on the web: http://www.octave.org >> How to fund new projects: http://www.octave.org/funding.html >> Subscription information: http://www.octave.org/archive.html >> ------------------------------------------------------------- > > -- > David Bateman David dot Bateman at motorola dot com > Motorola CRM +33 1 69 35 48 04 (Ph) > Parc Les Algorithmes, Commune de St Aubin +33 1 69 35 77 01 (Fax) > 91193 Gif-Sur-Yvette FRANCE > > The information contained in this communication has been classified as: > > [x] General Business Information > [ ] Motorola Internal Use Only > [ ] Motorola Confidential Proprietary > > > > ------------------------------------------------------------- > Octave is freely available under the terms of the GNU GPL. > > Octave's home on the web: http://www.octave.org > How to fund new projects: http://www.octave.org/funding.html > Subscription information: http://www.octave.org/archive.html > ------------------------------------------------------------- > ------------------------------------------------------------- Octave is freely available under the terms of the GNU GPL. Octave's home on the web: http://www.octave.org How to fund new projects: http://www.octave.org/funding.html Subscription information: http://www.octave.org/archive.html -------------------------------------------------------------