[SciPy-dev] Problem with flapack

Heiko Henkelmann heiko at hhenkelmann.de
Fri Feb 15 15:33:49 CST 2002


If a polynomial has only real and conjugate complex roots the coefficients
are real. This is a very easy way to determine if the coefficients of a
polynomial can be polished to real.

Heiko
----- Original Message -----
From: "Fernando Pérez" <fperez at pizero.colorado.edu>
To: <scipy-dev at scipy.org>
Sent: Friday, February 15, 2002 10:15 PM
Subject: Re: [SciPy-dev] Problem with flapack


> >
> > Sure, but I agree with Heiko that tiny zeros should be detected
internally and
> > cleaned up automatically.
>
> Careful. I can't think off the top of my head of a concrete example, but I
can
> impgine easily cases where you really have an unusual mix of roots with
> significant real parts and tiny imaginary components. In fact, in some of
my
> work something similar happens as certain parameters change and
eigenvalues
> for a certain operator start migrating off the real axis.
>
> So I would rather have the numerical algorithms spit out whatever answer
they
> get and let *me* do any cosmetic cleanup I want to after the fact. If we
want
> convenience, a keyword parameter, *off* by default, could control this
cleanup
> to be done internally. Call me old-fashioned, but I prefer numerics to
spit
> out whatever they get, without trying to get too smart.
>
> Of course, in cases where one has a bulletproof argument for cutting off
> spurious values, fine. But those cases are rare enough that I'd rather see
the
> garbage and clean it myself (or at least have that option until I'm
convinced
> it's really garbage, and then I can turn  the 'auto_cleanup' on).
>
> Just a thought,
>
> f.
>
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