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Re: problem with consistency of root finding and sorting
From: |
David Bateman |
Subject: |
Re: problem with consistency of root finding and sorting |
Date: |
Wed, 10 Oct 2007 02:23:51 +0200 |
User-agent: |
Thunderbird 1.5.0.7 (X11/20060921) |
Ben Abbott wrote:
> I have Octave 2.9.14 on Mac OS X (intel & PPC) installed via Fink and
> am concerned that my installations are giving different results than
> others.
>
> During the process of modifying residue.m so that it would function
> in a manner consistent with Matlab's I've become suspicious that my
> Octave installation does not work the same as others.
>
> The difference is small, but is troublesome.
>
> Given the following short example,
>
> r = sort(roots([1 0 18 0 81]))
> r_err = r - round(r)
>
> I obtain the results below
>
> r = sort(roots([1 0 18 0 81]))
> r =
>
> 0.0000 - 3.0000i
> 0.0000 + 3.0000i
> -0.0000 - 3.0000i
> -0.0000 + 3.0000i
>
> r_err = r - round(r)
> r_err =
>
> 2.5814e-08 + 1.6920e-08i
> 2.5814e-08 - 1.6920e-08i
> -2.5814e-08 - 1.6920e-08i
> -2.5814e-08 + 1.6920e-08i
Under Octave 2.9.14 compiled with g++ 4.0.1 on a Mandriva 2006 machine I get
octave:3> r = sort(roots([1 0 18 0 81]))
r =
0.0000 - 3.0000i
0.0000 + 3.0000i
-0.0000 - 3.0000i
-0.0000 + 3.0000i
octave:4> r_err = r - round(r)
r_err =
1.5973e-08 + 6.5742e-09i
1.5973e-08 - 6.5742e-09i
-1.5973e-08 - 6.5742e-09i
-1.5973e-08 + 6.5742e-09i
D.
>
> I suspect that others are getting slightly different results.
> Specifically, some installations appear to be returning conjugate of
> "r" instead. I've posted the "r_err" because it appears larger than
> I'd expect.
>
> I'd appreciate if others would try to short script and post the
> result ... in the hope of isolating the problem.
>
> TiA
- problem with consistency of root finding and sorting, Ben Abbott, 2007/10/09
- Re: problem with consistency of root finding and sorting,
David Bateman <=
- Re: problem with consistency of root finding and sorting, Ben Abbott, 2007/10/09
- Re: problem with consistency of root finding and sorting, David Bateman, 2007/10/09
- Re: problem with consistency of root finding and sorting, Ben Abbott, 2007/10/09
- Re: problem with consistency of root finding and sorting, David Bateman, 2007/10/10
- Re: problem with consistency of root finding and sorting, Ben Abbott, 2007/10/10
- Re: problem with consistency of root finding and sorting, David Bateman, 2007/10/10
- Re: problem with consistency of root finding and sorting, Ben Abbott, 2007/10/10
- Re: problem with consistency of root finding and sorting, David Bateman, 2007/10/10
- Re: problem with consistency of root finding and sorting, Ben Abbott, 2007/10/10
- Re: problem with consistency of root finding and sorting, David Bateman, 2007/10/10