[scilab-Users] Cascaded IIR filter design

[Sumit Adhikari]

Hello,
  Following is the way you can get poles and zeros

b = coeff(numer(hz));
a = coeff(denom(hz));

BR,
Sumit

Celso Co wrote:
> You may want to consider some means of manipulating poles and zeros in the
> attached file.  Celso
>
> -----Original Message-----
> From: Adelson Santos de Oliveira [mailto:adelson.oliveira at gmail.com]
> Sent: Saturday, July 25, 2009 10:03 AM
> To: users at lists.scilab.org
> Subject: Re: [scilab-Users] Cascaded IIR filter design
>
>
> Sorry,
> I would like to help but I can make only general comments. I would not
> go into the subject of your work.
> If hz were a Scilab polynomial, getting poles and zeroes would be
> straightforward from numerator and denominator ...
>
> I can only suggest you find a way to decompose hz into scilab objects
> (polys, ....),
>
> Good luck,
>
> Adelson
>
> Markus Svilans escreveu:
>   
>> Hi Adelson,
>>
>> Thanks for your response.
>> I think hz must be a Scilab rational polynomial. Here are its contents:
>>
>> -->hz
>> hz  =
>>
>>                                       2            3
>> 4            5            6  - 0.0513754 + 0.0469923z - 0.0057700z +
>> 2.282D-17z + 0.0057700z - 0.0469923z + 0.0513754z
>> --------------------------------------------------------------------------
>>     
> -------------
>   
>>                                           2            3
>> 4            5   6             0.5046613 - 1.0416559z + 2.4270369z -
>> 2.6222075z + 2.9969513z - 1.6458787z + z
>>
>> From what I have been able to research so far, I am starting to feel
>> that it's not possible to get Scilab to directly return the a,b
>> cascaded IIR coefficients.
>>
>> Perhaps, could you lend your expertise on these related questions:
>> 1. How to get the poles of hz?
>> 2. How to get the zeroes of hz?
>>
>> Knowing the poles and zeroes, I can hope to derive the IIR
>> coefficients by hand.
>>
>> Thanks very much,
>> Markus.
>>
>>
>>
>> Adelson Santos de Oliveira wrote:
>>     
>>> Sorry,
>>>
>>> I did not analyse your program. I supposed that hz is a polinomial
>>> according to SCILAB definition. See the following example and check
>>> if you can adapt it to your needs,
>>>
>>>
>>> Polz=poly([1,2,3],'Z','coefs')       <= this define a polynomial in
>>> variable Z, maybe your hz is not a polynomial for SCILAB
>>>
>>> coefz=coeff(Polz)                        <= this will return the
>>> coefficients 1, 2, and 3
>>>
>>>
>>> Markus Svilans escreveu:
>>>       
>>>> Adelson,
>>>>
>>>> Thanks for your response.
>>>>
>>>> It doesn't seem to work. The error message I get is:
>>>>
>>>> --
>>>> Function not defined for given argument type(s),
>>>>
>>>>  check arguments or define function %r_coeff for overloading.
>>>> --
>>>>
>>>> I'm looking for a way to get the b0, b1, a1, b2, a2, ...
>>>> coefficients required for a cascaded IIR. From what I understand,
>>>> there is an algorithm by which they are computed from the z-domain
>>>> coefficients hz.
>>>>
>>>> Regards,
>>>> Markus.
>>>>
>>>>
>>>> Adelson Santos de Oliveira wrote:
>>>>         
>>>>> Do you mean,
>>>>>
>>>>> coef_hz=coeff(hz) ?
>>>>>
>>>>> coef_hz is a vector with the coefficients of hz.
>>>>>
>>>>> coefhz=coeff
>>>>> Markus Svilans escreveu:
>>>>>           
>>>>>> Hello,
>>>>>>
>>>>>> I would like to use Scilab to design a cascaded IIR filter.
>>>>>>
>>>>>> I'm able to design a filter using iir(), as in the following example
>>>>>> code:
>>>>>>
>>>>>> ystr=[ 'type (lp, hp, bp, sb) ';
>>>>>>    'order (integer)';
>>>>>>    'design (butt, cheb1, cheb2 , ellip)' ;
>>>>>>    'cut-off frequencies (2-vector in [0, 0.5])';
>>>>>>    'error values  0 delta(1),delta(2) 1 '];
>>>>>> w = x_mdialog('Choose filter type and parameters',...
>>>>>>    ystr,['bp';'3';'ellip';'0.15 0.25';'0.08 0.035'])
>>>>>>
>>>>>> if w<>[] then
>>>>>>  hz=iir(evstr(w(2)),w(1),w(3),evstr(w(4)),evstr(w(5)));
>>>>>>  [hzm,fr]=frmag(hz,256);
>>>>>>  xselect();
>>>>>>  plot2d(fr',hzm')
>>>>>>  xtitle('Discrete IIR filter '+'( '+ w(3)+' ) ',' ',' ');
>>>>>>
>>>>>>  hz
>>>>>> end
>>>>>>
>>>>>> My question is, how can I convert the z domain expression in hz to a
>>>>>> set of coefficients suitable for use in a cascaded IIR filter
>>>>>> implementation? Any help would be greatly appreciated.
>>>>>>
>>>>>> Best regards,
>>>>>> Markus.
>>>>>>
>>>>>> (also posted in the comp.soft-sys.math.scilab group)
>>>>>>
>>>>>>
>>>>>>             
>>>>         
>>     


-- 

--------------------------------------------
Sumit Adhikari
System Design Engineer
austriamicrosystems AG
Business Unit : Automotive
Mob : 00-91-9885271710/00-91-9000161710


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