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Re: 8.0 Control Systems ToDiscreteTimeModel[]

  • To: mathgroup at smc.vnet.net
  • Subject: [mg114590] Re: 8.0 Control Systems ToDiscreteTimeModel[]
  • From: "Nasser M. Abbasi" <nma at 12000.org>
  • Date: Thu, 9 Dec 2010 06:02:10 -0500 (EST)
  • References: <idnqs7$q7d$1@smc.vnet.net>
  • Reply-to: nma at 12000.org

On 12/8/2010 3:40 AM, roby wrote:

>
> ToDiscreteTimeModel[TransferFunctionModel[s, s], Ts, z] // InputForm
>
> With the default Option Method->"BilinearTransform" I would expect
> something like:
>
> TransferFunctionModel[{{{2*(-1 + z)}}, {{Ts*(1 + z)}}}, z,
> SamplingPeriod ->  Ts]
>
>
> but what is returned actualy seems to be some bug/crash:
>
> TransferFunctionModel[{{{2*(-1 + z)}},
> {{Control`ConversionsDump`sdmult$927}}}, z,
>   SamplingPeriod ->  Ts]
>
>
> Any hints, am I missing something ?
>
> Regards Robert
>

H(s) = s is NOT a realizable transfer function.

In H(s) = NUM(s)/DEN(s), the numerator degree in 's' can't be greater than the degree in 's' of the denominator's.  (for a real system).

In your case, it is greater, since NUM(s)=s^1, and DEN(s)=1=s^0

--Nasser



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