Re: chol problem in 2.9.5

[Quentin Spencer]

Dmitri A. Sergatskov wrote:
> octave:1> a=randn(2)
> a =
>
>  -0.94562   1.05567
>  -0.69245   1.99836
>
> octave:2> x=a'*a
> x =
>
>   1.3737  -2.3820
>  -2.3820   5.1079
>
> octave:3> chol(x)
> ans =
>
>   1.17204  -2.03238
>   0.00000   0.98860
> Upper Triangular
>
> octave:4> chol(x)
> error: chol: matrix not positive definite
> octave:4>
> ---
>
> So after calling chol a second time on the same matrix it gives an error.
> That seems breaks chol for good for remaining of the octave session:
>
> octave:4> a=randn(2)
> a =
>
>  -0.081825   0.226121
>   0.273070   0.446935
>
> octave:5> y=a'*a
> y =
>
>  0.081263  0.103542
>  0.103542  0.250882
>
> octave:6> chol(y)
> error: chol: matrix not positive definite
> octave:6>
>
> This is octave-2.9.5-3.fc5 rpm on x86_64 Fedora Core 5.

I can't duplicate this on i386 with the same FC5 rpm. I suppose this 
could be specific to x86_64, but I don't know why.
Is the checking for positive definiteness done by octave or lapack?

Quentin