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Re: residue() confusion


From: Ben Abbott
Subject: Re: residue() confusion
Date: Sat, 22 Sep 2007 20:23:36 -0700 (PDT)

I posted to one of the Fink forums and got this response

http://www.nabble.com/Trouble-with-Octave-tf4502632.html#a12842513

Apparently, the problem is with 2.9.13 and earlier. Can someone confirm?


Ben Abbott wrote:
> 
> ok ... sigh ... I just noticed that 
> http://www.nabble.com/bug-in-residue.m-tf4475396.html Hodel's  original
> post has the same answer as I derived and is consistent with Matlab.
> 
> So no my question is ...
> 
> Does anyone's Octave installation give the wrong answer?
> 
> Specifically is there someone with a Mac who used Fink to install Octave,
> and what does their installation give for
> 
> num = [1 0 1];
> den = [1 0 18 0 81];
> [a,p,k,e] = residue(num,den)
> 
> 
> 
> Ben Abbott wrote:
>> 
>> ok, I did some quick math
>> 
>> (x^2+1)/(x^4+18*x^2+81) = (2/9)/(x-3i) + (2/9)/(x+3i) + (1/54i)/(x-3i)^2
>> - (1/54i)/(x+3i)^2
>> 
>> Thus,
>> 
>> a = [1/54i 2/9 -1/54i 2/9]
>> p = [3i 3i -3i -3i]
>> k = []
>> e = [2 1 2 1]
>> 
>> Can someone confirm they are able to get the correct answer from their
>> installation of Octave? 
>> 
>> I'm running 2.9.13 on both PPC and Intel based Macs
>> 
>> 
>> Ben Abbott wrote:
>>> 
>>> Regarding the various results, I was more concerned about the
>>> differences in "a" ... the pole locations are consistent but their
>>> residues are different.
>>> 
>>> 
>>> Henry F. Mollet wrote:
>>>> 
>>>> The result for e should be [1 2 1 2] (multiplicity for both poles).
>>>> Note
>>>> that Matlab does not even give e.  My mis-understanding of the problem
>>>> was
>>>> pointed out by Doug Stewart. Doug posted new code yesterday, which I've
>>>> tried unsuccessfully, but I cannot be sure that I've implemented
>>>> residual.m
>>>> correctly. The corrected code still produced e = [1 1 1 1] for me.
>>>> Henry
>>>> 
>>>> 
>>>> on 9/22/07 1:31 PM, Ben Abbott at address@hidden wrote:
>>>> 
>>>>> 
>>>>> As a result of reading through Hodel's
>>>>> http://www.nabble.com/bug-in-residue.m-tf4475396.html post  I decided
>>>>> to
>>>>> check to see how my Octave installation and my Matlab installation
>>>>> responded
>>>>> to the example
>>>>> 
>>>>> Using Matlab v7.3
>>>>> --------------------------
>>>>>  num = [1 0 1];
>>>>>  den = [1 0 18 0 81];
>>>>>  [a,p,k] = residue(num,den)
>>>>> 
>>>>> a =
>>>>> 
>>>>>         0 - 0.0926i
>>>>>    0.2222 - 0.0000i
>>>>>         0 + 0.0926i
>>>>>    0.2222 + 0.0000i
>>>>> 
>>>>> 
>>>>> p =
>>>>> 
>>>>>    0.0000 + 3.0000i
>>>>>    0.0000 + 3.0000i
>>>>>    0.0000 - 3.0000i
>>>>>    0.0000 - 3.0000i
>>>>> 
>>>>> 
>>>>> k =
>>>>> 
>>>>>      []
>>>>> --------------------------
>>>>> 
>>>>> Using Octave 2.9.13 (via Fink) on Mac OSX
>>>>> --------------------------
>>>>>  num = [1 0 1];
>>>>>  den = [1 0 18 0 81];
>>>>>  [a,p,k] = residue(num,den)
>>>>> 
>>>>> a =
>>>>> 
>>>>>   -3.0108e+06 - 1.9734e+06i
>>>>>   -3.0108e+06 + 1.9734e+06i
>>>>>   3.0108e+06 + 1.9734e+06i
>>>>>   3.0108e+06 - 1.9734e+06i
>>>>> 
>>>>> p =
>>>>> 
>>>>>   -0.0000 + 3.0000i
>>>>>   -0.0000 - 3.0000i
>>>>>    0.0000 + 3.0000i
>>>>>    0.0000 - 3.0000i
>>>>> 
>>>>> k = [](0x0)
>>>>> e =
>>>>> 
>>>>>    1
>>>>>    1
>>>>>    1
>>>>>    1
>>>>> --------------------------
>>>>> 
>>>>> These are different from both the result that
>>>>> http://www.nabble.com/bug-in-residue.m-tf4475396.html Hodel obtained ,
>>>>> as
>>>>> well as different from
>>>>> http://www.nabble.com/bug-in-residue.m-tf4475396.html Mollet's
>>>>> 
>>>>> Thoughts anyone?
>>>>> 
>>>> 
>>>> 
>>>> _______________________________________________
>>>> Help-octave mailing list
>>>> address@hidden
>>>> https://www.cae.wisc.edu/mailman/listinfo/help-octave
>>>> 
>>>> 
>>> 
>>> 
>> 
>> 
> 
> 

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