Python Forum
How to use Scipy.special to retrieve complex Poles / Zeros of Bessel Polynominal - Printable Version

+- Python Forum (https://python-forum.io)
+-- Forum: Python Coding (https://python-forum.io/forum-7.html)
+--- Forum: Data Science (https://python-forum.io/forum-44.html)
+--- Thread: How to use Scipy.special to retrieve complex Poles / Zeros of Bessel Polynominal (/thread-23459.html)

How to use Scipy.special to retrieve complex Poles / Zeros of Bessel Polynominal - Detzi - Dec-31-2019

Good Day,
i am trying to calculate the Poles of a Bessel Polynomial as it is used in electronics. [1] after a bit of searching i found the scipy.special module [2] and its dedicated functions to calculate the zero of the bessel function. [3]
Since i need the output to be a complex number in the form of 
Output:
z=a+bj
where "j" is the imaginary number, i thought that 
special.y0_zeros(2,True)
or
special.y1_zeros(2,True)
or
special.y1p_zeros(2,True)
should give me a number close to the ones listed in the Table that can be found under [4] but it doesn't. I tried to get the numbers for a second order Filter here and the output is (reformated):
Output:
special.y0_zeros(2,True)
[-2.40301663+0.53988231j, -5.5198767 +0.54718001j]
[ 0.10074769-0.88196771j, -0.02924642+0.5871695j ]
special.y1_zeros(2,True)
[-0.50274327+0.78624371j, -3.83353519+0.56235654j]
[-0.45952768+1.31710194j,  0.04830191-0.69251288j]
special.y1p_zeros(2,True)
[ 0.57678513+0.90398479j, -1.94047734+0.72118592j]
[-0.76349709+0.58924486j,  0.16206401-0.95202789j]
what i would have expected is:
Output:
-1.1030+-0.6368j
Also the Output for the same with a "1" instead of a "2" isn't just "1" which i also would have expected from the given table.
Now i am no mathematician and i really have no clue about most of the terminology used so i am having a hard time figuring out if scipy can do what i need at all and if yes which function listed under [3] then is the right one to use and most importantly why Huh
Maybe someone here can hook me up, thanks in advance!

RE: How to use Scipy.special to retrieve complex Poles / Zeros of Bessel Polynominal - Gribouillis - Dec-31-2019

I don't know this subject, but wouldn't scipy.signal.bessel be more adapted? It seems to give poles as a member of the structure.

RE: How to use Scipy.special to retrieve complex Poles / Zeros of Bessel Polynominal - Detzi - Dec-31-2019

Wall i wasn't aware of that, i will definitely have a closer look at this, thanks a lot!
But still i really would like to understand the thing as a whole...like doing it from scratch.