
From:  dastew 
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 GutiĆ©rrez 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 > > OctaveForge 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 :) Doug 
[Prev in Thread]  Current Thread  [Next in Thread] 