[Numpy-discussion] Problem in LinearAlgebra?

[Rob Hooft]

Nadav Horesh wrote:
> I tested the problem with:
>      1. Numeric 23.1 under python 2.3.2
>      2. numarray 0.8 (I made a copy of the Scientific package where all
>         calls to Numeric were replaced to numarray), under python 2.3.2
> There results where about the same -- high coefficients for the 5th
> order polynomials.
> I would expect reliable fit for a high order polynomials only under very
> special circumstances, so this is not a big surprise. 

Thanks for your efforts.

The polynomial we're trying to fit here is not extremely unstable. As I 
said, with Numeric 17.1.2 my class of problems used to be stable up to 
at least 9th order. I really suspect a bug was introduced here which is 
difficult to pinpoint because everybody reacts the natural way: this is 
an intrinsicly unstable problem, so it is not unexpected. Somehow it 
could have been better, though!

I managed to work around the problem so far by using a different solver 
also built in to Scientific Python, so I am saved so far.

Regards,

Rob

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Rob W.W. Hooft  ||  rob at hooft.net  ||  http://www.hooft.net/people/rob/