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Re: half-assed rcond


From: Søren Hauberg
Subject: Re: half-assed rcond
Date: Sat, 01 Sep 2007 13:58:55 +0200
User-agent: Thunderbird 1.5.0.13 (X11/20070824)

David Bateman skrev:
Søren Hauberg wrote:
Hi,
  For some time I've been using some written-for-matlab code that
requires the 'rcond' function, which Octave doesn't have. For this I've
been using the following half-assed implementation:

function rc = rcond(A)
  [dont_care, rc] = det(A);
endfunction

Just wondering if you wanted a documented, error-checking, etc., version
of the above code, or if that implementation is too in-efficient?

Søren



Why not use

function rc = rcond (A)
  [dum, rc] = inv (A);
endfunction

This isn't half-assed though you pay the cost of an additional back
substitution to form the inverse from the factorization when you don't
really need it.
The choice to use 'det', was at best random, so I'll be sure to use 'inv' from now on. The reason I posted, was mostly to hear if Octave should have an implementation of 'rcond' based on such a simple implementation.

Thanks,
  Søren


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