|
From: | Marco Caliari |
Subject: | Re: Improved normest |
Date: | Thu, 26 Nov 2009 14:09:48 +0100 (CET) |
User-agent: | Alpine 1.00 (DEB 882 2007-12-20) |
On Thu, 26 Nov 2009, Jaroslav Hajek wrote:
On Thu, Nov 26, 2009 at 12:19 PM, Marco Caliari <address@hidden>wrote:Dear maintainers, I have seen changeset http://hg.savannah.gnu.org/hgweb/octave/rev/87595d714005 about normest, by Jaroslav. As already discussed, the choice x = norm (A, "columns").' for the initial vector leads to wrong values (second largest eigenvalue) for some "important" matrices, like toeplitz([-2,1,zeros(1,2)]), toeplitz([-2,1,zeros(1,4)]), etc This was the reason for the old random initial vector. I agree it is not nice to have slightly different results at each run, but it is not nice to have wrong values, too. Best regards, MarcoAlready discussed? When? I couldn't find anything.
Here, even if the choice for the initial vector was different http://www-old.cae.wisc.edu/pipermail/octave-maintainers/2006-December/001422.html
It's no problem to randomize it again, but I think a non-random behavior is preferable.
I agree.
Can the initial vector be improved somehow?
I have no idea. It is usually written "take the initial vector you want: roundoff errors will do the rest".
Cheers, Marco
[Prev in Thread] | Current Thread | [Next in Thread] |