From: Calamitas <calamitates@...>
Date: 2008-12-24T01:37:31+09:00
Subject: [ruby-core:20836] Re: matrix.rb dyscalculic about determinants in 1.8.x

On Tue, Dec 23, 2008 at 5:22 PM, Christian Neukirchen
<chneukirchen@gmail.com> wrote:
> Bug as of Ruby 1.6.x--1.8.x (has been fixed in trunk as of revision 5599
> without explicit mention as far as I can tell):
>
> Maxima 5.14.0
> (%i25) determinant(matrix([2,1],[1,-1]));
> (%o25)                                - 3
>
> Mathematica 6.0
> In[1]:= Det[{{2, 1}, {1, -1}}]
> Out[1]= -3
>
> Cramer's rule:
> 2*(-1) - 1*1 = -3
>
> But Ruby's matrix.rb says:
>
>>> Matrix[[2,1],[1,-1]].det
> => -2

>> require 'matrix'
=> true
>> Matrix[[2,1],[1,-1]].det
=> -2
>> require 'mathn'
=> true
>> Matrix[[2,1],[1,-1]].det
=> -3

This is mentioned in the Pickaxe.

This of course says nothing about why trunk returns the correct result.

Peter