Re: Octave hangs forever trying to invert singular matrix

[Carlo de Falco]

On 22 Dec 2009, at 19:17, Carlo de Falco wrote:

> Hi,
>
> I have a 480x480 sparse matrix of rank 479
> trying to solve
>
> A\ones(480,1)
>
> makes matlab throw a warning and return garbage
>
> >> A\ones(480,1)
> Warning: Matrix is close to singular or badly scaled.
>        Results may be inaccurate. RCOND = 3.815118e-20.
>
> ans =
>
>  1.0e+17 *
>
>  -0.2637
>  -0.2637
>  -0.2637
>  -0.2637
>  -0.2637
>  -0.2637
>  -0.2637
>
> on the other hand Octave hangs forever.
> Is there a way to check before-hand whether the system can be solved  
> to prevent Octave from going into "Guru meditation mode"?
> Is this to be considered a bug?
>
> I am using Thomas' 3.2.3 binary on Mac OS X.
> c.

If anyone wants to try with the particular matrix that showed the  
problem for me, it can be found here:
http://mox.polimi.it/~carlo/calnum/A.mat

c.