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## Re: octave-forge lin.alg. kernel/image/span

 From: Geordie McBain Subject: Re: octave-forge lin.alg. kernel/image/span Date: Tue, 20 Jun 2006 12:39:34 +1000

To investigate the use of the second, TOL, argument to null, try:

octave> A = [1, 2, 1; 1, 2, 2];
octave> null (A, 0.1)
ans =

-8.9443e-01
4.4721e-01
-6.0501e-16

octave> null (A, 1)
ans =

-2.5510e-01   -8.9443e-01
-5.1021e-01    4.4721e-01
8.2134e-01   -6.0501e-16

octave> null (A, 10)
ans =

-3.6732e-01   -2.5510e-01   -8.9443e-01
-7.3463e-01   -5.1021e-01    4.4721e-01
-5.7043e-01    8.2134e-01   -6.0501e-16

I don't know about the `don't orthogonalize' parameter.

On Tue, 2006-06-20 at 03:41 +0200, Stefan de Konink wrote:
> Hello,
>
>
> Before I start hacking on something. Are any kernel/image functions
> currently available in octave-forge?
>
> I found in a matlab lecture the null() function should be used. But:
>
> A = [ 1 1; 0 0 ];
> A * null(A)
>
> does [0 0] for me.
>
> But using:
> A = [1 2 1; 1 2 2];
> A * null(A, 'r')
> Remark 5.1  The parameter 'r' above is used so that MATLAB does not
> orthogonalize the basis; that is, it does not change the vectors in the
> basis to be of unit length and perpendicular to each other.
>
> Does't get me there.
> null(A, 'r') as on slide should produce [-2 ; 1 ; 0 ]
>
> octave:39> null(A)
> ans =
>
>    -8.9443e-01
>     4.4721e-01
>     2.6223e-16
>
> According to the help function I can specify a TOL to limit the number of
> SVD values which doesn't give the expected result.
>
>
> Any advice on this subject?
>
>
> Yours Sincerely,
>
> Stefan de Konink
>
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