Re: bug in residue.m

> I had no problem with your example if I understood the problem correctly.
> p appeared without having to sort. I had slight problem with inputing "den"
> using copy/past from posting.
> Octave 2.9.13 on Mac OS X.
> Henry
>
> octave-2.9.13:9> num = [1,0,1];
> octave-2.9.13:11> den =\302\240 [1,0,18,0,81]
> error: invalid character `?' (ASCII 194) near line 11, column 7
> parse error:
>   syntax error
>  
>>>> den =  [1,0,18,0,81]
>>>>        
>          ^
> octave-2.9.13:11> den = [1,0,18,0,81];
>
> octave-2.9.13:13> [a,p,k,e] = residue(num,den)
> a =
>
>   8.4492e+06 - 3.9658e+06i
>   8.4492e+06 + 3.9658e+06i
>   -8.4492e+06 + 3.9658e+06i
>   -8.4492e+06 - 3.9658e+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
>
>  

> octave-2.9.13:14> help residue
> *****************************************************
>
>
> on 9/18/07 8:44 AM, A. Scottedward Hodel at hodelas@... wrote:
>
>  
>> Octave 2.9.13 on Mac OS X:
>> The m-file below reveals a problem in residue.m,  in Octave's
>> polynomial scripts.  I started to debug it, but the
>> code is fairly intricate.  The problem is that the code fails to
>> detect multiple roots.
>> Consider the case:
>>
>> octave:7> num = [1,0,1];
>> octave:7> den =  [1,0,18,0,81];
>> octave:8> [a,p,k,e] = residue(num,den)
>>
>> fails to detect the multiple poles at +/- j3 on my machine.  The
>> problem appears to be that residue expects the roots to be returned
>> in a specific order.  The problem in this case is resolved by sorting
>> the poles by their imaginary parts.
>>
>> octave:9> %sort poles by imaginary part
>> octave:9> [a,p,k,e] = residue(num,den)
>> a =
>>
>>    7.3527e-25 + 9.2593e-02i
>>    2.2222e-01 + 2.3902e-09i
>>    -3.6764e-25 - 9.2593e-02i
>>    2.2222e-01 + 2.3902e-09i
>>
>> p =
>>
>>    -0.0000 - 3.0000i
>>     0.0000 - 3.0000i
>>     0.0000 + 3.0000i
>>    -0.0000 + 3.0000i
>>
>> k = [](0x0)
>> e =
>>
>>     1
>>     2
>>     1
>>     2
>>
>>    

>> The change to residue.m is in the following diff:  Note This will fix
>> my problem, but it can still break if two pairs of complex poles have
>> the same imaginary part, e.g., if you have poles at
>> 1+j, 1-j, -1+j, and -1-j,
>> if they are sorted in  order of imaginary part
>> -1+j,1+j,-1-j, 1-j,
>> then the code will still fail to detect the multiplicity.  The
>> details of the code are complicated enough that I can't propose a
>> proper fix right now, but this patch will fix the problem cited above.
>>
>> *** /sw/share/octave/2.9.13/m/polynomial/residue.m      Fri Sep  7
>> 09:44:44 2007
>> --- residue.m   Tue Sep 18 10:38:20 2007
>> ***************
>> *** 201,207 ****
>>
>>      ## Find the poles.
>>
>> !   p = roots (a);
>>      lp = length (p);
>>
>>      ## Determine if the poles are (effectively) zero.
>> --- 201,207 ----
>>
>>      ## Find the poles.
>>
>> !   p = sortcom(roots (a), "im");
>>      lp = length (p);
>>
>>      ## Determine if the poles are (effectively) zero.
>>
>>
>> A. Scottedward Hodel hodelas@...
>> http://homepage.mac.com/hodelas/tar
>>
>>
>> _______________________________________________
>> Help-octave mailing list
>> Help-octave@...
>> https://www.cae.wisc.edu/mailman/listinfo/help-octave
>>    
>
>
>
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