|Subject:||RE: Some Octave newbie questions regarding number format and matrices|
|Date:||Sun, 20 Sep 2009 13:54:42 +0000|
> Date: Sun, 20 Sep 2009 04:32:35 -0700
> From: address@hidden
> To: address@hidden
> Subject: Re: Some Octave newbie questions regarding number format and matrices
> Jordi Gutiérrez Hermos wrote:
> > 2009/9/19 hdfrango :
> >> 1. is there any way to force octave to express numbers in fraction form,
> >> to
> >> avoid loss of precision?
> > If you don't want to lose precision, you need a symbolic CAS, like
> > Sage or Maxima, not Octave. Octave is optimised for speed with
> > hardware floats, and although it does have a symbolic addon in the
> > Octave-Forge packages, this is more of an afterthought than core
> > functionality. In particular, it only allows you to change the
> > precision. I don't believe a bignum interface exists for Octave.
> >> 2. when I want to computer the inverse of a matrix, I have to do inv(A'),
> >> computing the inverse of the transpose, in order to get the correct
> >> answer.
> >> Why is that?
> > My guess is that you've either found a bizarre bug in Octave, or you
> > are confused about what the inverse of a matrix should be. Can you
> > show us a specific matrix for which inv(A) produces the transpose of
> > the correct inverse?
> > - Jordi G. H
> First of all thank you both for the replies.
> 1. I will give the tools mentioned a try.
> 2. As for the matrix issue, I feel really stupid, it turns out even though I
> knew how to correctly input a matrix in octave, I was somehow entering the
> transpose, which is why I needed to compute the inverse of the transpose in
> order to get the expected result :).
> thanks again
Hey. we all have done something like that in the past so smile.
If you have any more questions , just ask :-)
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