[Numpy-discussion] Problem in LinearAlgebra?
nadavh at visionsense.com
Sun Nov 2 07:53:17 CST 2003
Many unstable problems have a stable solution if you choose the right
algorithm. The question is if somewhere the developers decided to switch
the equations solver, or there is a real bug. I hope that one of the
developers will reply in this forum. I will try to look at it also,
since it is a core component in the linear algebra package. Also if you
suspect that your work-around is useful --- please post it here!
Rob Hooft wrote:
> 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.
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