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Re: Some Octave newbie questions regarding number format and matrices

From: hdfrango
Subject: Re: Some Octave newbie questions regarding number format and matrices
Date: Sun, 20 Sep 2009 04:32:35 -0700 (PDT)

Jordi GutiƩrrez 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

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