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Re: Same .m file: different results with different versions of Octave
From: |
Jaroslav Hajek |
Subject: |
Re: Same .m file: different results with different versions of Octave |
Date: |
Mon, 19 Apr 2010 09:55:42 +0200 |
On Mon, Apr 19, 2010 at 9:20 AM, Judd Storrs <address@hidden> wrote:
> On Mon, Apr 19, 2010 at 3:11 AM, Jaroslav Hajek <address@hidden> wrote:
>> One minor drawback I can immediately see is that these formulas don't
>> always reduce to plain tanh (R) when I = 0. Indeed, the result may be
>> a bit off even for small numbers:
>>
>> octave:1> tanh(complex(1,0)) - tanh(1)
>> ans = 0
>> octave:2> testgsltanh(complex(1,0)) - tanh(1)
>> ans = 1.1102e-16
>
> Isn't that less than machine precision:
>
>> tanh(1)*eps
> ans = 1.6911e-16
>
Yes, but it's not zero. Accordingly, in some circumstances an m-file
function may give slightly different results from an apparently
equivalent C++ implementation. This is because Octave will
automatically narrow down complex intermediate results with zero
imaginary part. It's not serious, but the current implementation
doesn't seem to suffer from this.
--
RNDr. Jaroslav Hajek, PhD
computing expert & GNU Octave developer
Aeronautical Research and Test Institute (VZLU)
Prague, Czech Republic
url: www.highegg.matfyz.cz
- Re: Same .m file: different results with different versions of Octave, (continued)
- Re: Same .m file: different results with different versions of Octave, Judd Storrs, 2010/04/17
- Re: Same .m file: different results with different versions of Octave, perseu.as, 2010/04/17
- Re: Same .m file: different results with different versions of Octave, Thomas D. Dean, 2010/04/17
- Re: Same .m file: different results with different versions of Octave, Judd Storrs, 2010/04/18
- Re: Same .m file: different results with different versions of Octave, Thomas D. Dean, 2010/04/18
- Re: Same .m file: different results with different versions of Octave, perseu.as, 2010/04/18
- Re: Same .m file: different results with different versions of Octave, John W. Eaton, 2010/04/18
- Re: Same .m file: different results with different versions of Octave, Judd Storrs, 2010/04/18
- Re: Same .m file: different results with different versions of Octave, Jaroslav Hajek, 2010/04/19
- Re: Same .m file: different results with different versions of Octave, Judd Storrs, 2010/04/19
- Re: Same .m file: different results with different versions of Octave,
Jaroslav Hajek <=
- Re: Same .m file: different results with different versions of Octave, John W. Eaton, 2010/04/18
- Re: Same .m file: different results with different versions of Octave, Judd Storrs, 2010/04/18
- Re: Same .m file: different results with different versions of Octave, John W. Eaton, 2010/04/18
- Re: Same .m file: different results with different versions of Octave, Judd Storrs, 2010/04/18
- Re: Same .m file: different results with different versions of Octave, Jaroslav Hajek, 2010/04/18
- Re: Same .m file: different results with different versions of Octave, Judd Storrs, 2010/04/18
- Re: Same .m file: different results with different versions of Octave, Juergen Rose, 2010/04/19
- Re: Same .m file: different results with different versions of Octave, Jaroslav Hajek, 2010/04/19
- Re: Same .m file: different results with different versions of Octave, Søren Hauberg, 2010/04/19
- Re: Same .m file: different results with different versions of Octave, Judd Storrs, 2010/04/19