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Re: Inverse Matrix Function appears a bit wonky
From: |
David Bateman |
Subject: |
Re: Inverse Matrix Function appears a bit wonky |
Date: |
Thu, 4 Nov 2004 09:54:14 +0100 |
User-agent: |
Mutt/1.4.1i |
According to Robert A. Macy <address@hidden> (on 11/04/04):
> That's it! simply asking to return the value of rcond
> allows me to catch a "bad" matrix.
If you are after speed don't just ask for the condition number everytime.
If you have a good expectation that the matrix isn't singular, not
calculating the condition number is a speed gain.
Regards
David
>
> Thank you.
>
> - Robert -
>
> On Wed, 03 Nov 2004 14:08:34 -0700
> "Dmitri A. Sergatskov" <address@hidden> wrote:
> > Robert A. Macy wrote:
> > > I tried a simple test of the inverse function using a
> > "made
> > > up" matrix...
> > >
> > > testmatrix =
> > > 1 2 3 4
> > > 2 2 3 3
> > > 1 2 1 2
> > > 3 2 2 1
> >
> > Your matrix is no good. Set testmatrix(4,4)=-1 and try
> > again :)
> >
> > > What do I do to make certain octave doesn't do these
> > > erroneous inverse calculations the next time I go to
> > use
> > > the inverse function?
> > >
> >
> > Instead of b=inv(a), you can try [b,r]=inv(a), and check
> > that r is not too small.
> >
> > > - Robert -
> >
> > Cheers,
> >
> > Dmitri.
>
>
>
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--
David Bateman address@hidden
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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
-------------------------------------------------------------
Re: Inverse Matrix Function appears a bit wonky, Geraint Paul Bevan, 2004/11/03