[scilab-Users] z^(-1/2) half cycle delay in discrete time

[Serge Steer]

You can used the following toolbox

http://www.scilab.org/contrib/index_contrib.php?page=displayContribution&fileID=1189
Serge Steer

Le 10/05/2011 18:18, Dean Parsons a écrit :
> *David,*
> **
> *Thanks for your prompt response. Let me ask my question in a 
> different way.*
> **
> *In MATLAB I can add a delay to the input of a continuous time system 
> with the following code sequence:*
> **
> *time_delay = 0.5;*
> *sys_continuous_time = ss(A,B,C,D);*
> *set(sys_continuous_time,'InputDelay',time_delay*[1 1 1]);*
> **
> *In transfer funtion representation my sys_continuous_time = -1 - 1/s 
> - 1/s^2*
> *I believe the third line of code above multiples sys_continuous_time 
> by [exp(-0.5*s)   exp(-0.5*s)   exp(-0.5*s)] which is equivalent to 
> multiplying by [z^(-1/2)   z^(-1/2)   z^(-1/2)]*
> **
> *I know how to write Scilab code for the first 2 lines of code above. 
> My question is: Is there a way in Scilab to do what the 3rd line of 
> code above does?*
> **
> *If I try to create a term like exp(-0.5*s) or z^(-1/2) in Scilab in 
> order to do this multiplication, I get the following error messages:*
> **
> **
> *-->s=poly(0,"s");
>
> -->a = exp(-0.5*s);
>                 !--error 246
> Function not defined for given argument type(s),*
> **
> **
> *  check arguments or define function %p_exp for overloading.
> *
> *-->z = poly(0,"z");
>
> -->a = z^(-1/2);
>              !--error 30
> Invalid exponent.*
> **
> **
> *How can I add a half clock cycle of delay to the input of a 
> continuous time system in Scilab? (I am modeling a sigma delta 
> modulator which uses continuous time integrators as well as a sampling 
> quantizer which has a half clock cycle of delay - all in the same 
> loop. This is why it is necessary to have a mixture of continuous time 
> & discrete time math in the same system.)*
> *
> *
> **
> *Dean Parsons*
> **
> ****
>
>     ----- Original Message -----
>     *From:* David PICARD <mailto:d.picard at opgc.univ-bpclermont.fr>
>     *To:* users at lists.scilab.org <mailto:users at lists.scilab.org>
>     *Sent:* Tuesday, May 10, 2011 2:42 AM
>     *Subject:* Re: [scilab-Users] z^(-1/2) half cycle delay in
>     discrete time
>
>     z^-1 is the  value of the system 1 sampling period in the past.
>     But as sampling is discrete, does it make sense to reference a
>     value that is between 2 samples, but that does not exist in your
>     model, since, by definition, it is not sampled ?
>
>
>     Le 09/05/2011 19:27, Dean Parsons a écrit :
>>     *Hello,*
>>     **
>>     *I want to add a half cycle delay to a discrete time transfer
>>     function by multiplying the transfer function by z^(-0.5). It
>>     seems Scilab doesn't allow non-integer exponents with the
>>     discrete time variable z:*
>>     **
>>     *-->z=poly(0,"z");
>>
>>     -->a = z^(-0.5);
>>                  !--error 30
>>     Invalid exponent.
>>     *
>>     *Is there a work around for this? Is there another way to create
>>     the discrete time delay z^(-1/2)?*
>>     **
>>     *Thank you for your help with this.*
>>     **
>>     *Dean Parsons*
>>     **
>

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.scilab.org/pipermail/users/attachments/20110510/ceb42aa2/attachment.htm>