I think I have found another problem in residue.

[Ben Abbott]

On Dec 9, 2007, at 2:20 PM, Doug Stewart wrote:

> Ben Abbott wrote:
>>
>> On Dec 9, 2007, at 12:23 PM, Doug Stewart wrote:
>>
>>>
>>>
>> Doug, I took your example and modified it slightly. Please see the  
>> attached test script. The script displays [r, p]
>>
>> I've run the script from Octave on Tiger/PPC and Leopard/Intel, as  
>> well as on Matlab 7.3b. In each case I get the same results (except  
>> that matlab appears to refine the roots a bit better).
>>
>> ---------------------------
>> octave:30> test
>> ans =
>>
>>   -1.31921 +  0.00000i   -5.60000 +  0.00000i
>>   -3.79336 +  8.39318i   -2.99998 +  3.00009i
>>   14.55944 + 10.64154i   -3.00008 +  2.99997i
>>   16.35697 - 13.24746i   -2.99994 +  2.99994i
>>   -3.79336 -  8.39318i   -2.99998 -  3.00009i
>>   14.55944 - 10.64154i   -3.00008 -  2.99997i
>>   16.35697 + 13.24746i   -2.99994 -  2.99994i
>>    8.90592 -  0.00000i   -1.00000 +  0.00000i
>> ---------------------------
>>
>> The Matlab result is
>>
>> ---------------------------
>> >> test
>> ans =
>> -1.3195            -5.6000
>> -3.7929 + 8.3933i  -3.0000 + 3.0000i
>> 14.5590 +10.6397i  -3.0000 + 3.0000i
>> 16.3510 -13.2508i  -3.0000 + 3.0000i
>> -3.7929 - 8.3933i  -3.0000 - 3.0000i
>> 14.5590 -10.6397i  -3.0000 - 3.0000i
>> 16.3510 +13.2508i  -3.0000 - 3.0000i
>>  8.9054            -1.0000
>> ---------------------------
>>
>> It appears to me that Octave and Matlab's residue.m script work in  
>> compatible/consistent ways ... hmmm, perhaps I've misinterpreted  
>> your point?
>>
>> I'm on a tight schedule today, so I don't have time for doing a  
>> derivation by hand to verify the results. My presence online will  
>> be spotty for the next few days, but will check back when I can.
>>
>> Ben
>>
> OK!  Then the problem is at my end.
>
> I agree that this is a good answer from residue.
> Doug Stewart

Doug,

I'm curious, what version of Octave are you presently running, and on  
what platform?

Ben