Re: Inverse Matrix Function appears a bit wonky

[Dmitri A. Sergatskov]

Geraint Paul Bevan wrote:
> octave> inv (m)
> warning: inverse: matrix singular to machine precision, rcond = 0
> ans =
>
> ~  3.00000  2.00000  2.00000  1.00000
> ~  0.33333  1.33333  0.33333  1.66667
> ~  0.33333  1.00000  2.00000  2.00000
> ~  0.66667  0.50000  0.75000  0.00000

How come I do not get a warning?
(Octave 2.1.60 / ATLAS 2.7.8)
 octave:35> m = [1 2 3 4; 2 2 3 3; 1 2 1 2; 3 2 2 1];
octave:36> det (m)
ans =  -1.3323e-15
octave:37> inv (m)
ans =

   -4.5036e+15    6.0048e+15    1.5012e+15   -3.0024e+15
    4.5036e+15   -6.0048e+15   -1.5012e+15    3.0024e+15
    4.5036e+15   -6.0048e+15   -1.5012e+15    3.0024e+15
   -4.5036e+15    6.0048e+15    1.5012e+15   -3.0024e+15

octave:38> which inv
inv is a built-in function
octave:39> which inverse
inverse is a built-in function
octave:40> [x,r] = inv (m)
x =

   -4.5036e+15    6.0048e+15    1.5012e+15   -3.0024e+15
    4.5036e+15   -6.0048e+15   -1.5012e+15    3.0024e+15
    4.5036e+15   -6.0048e+15   -1.5012e+15    3.0024e+15
   -4.5036e+15    6.0048e+15    1.5012e+15   -3.0024e+15

r =  4.1633e-18


> - --
> Geraint Bevan
> http://homepage.ntlworld.com/geraint.bevan

--
Dmitri.



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