On Feb 26, 10:48 pm, "Rajiv Singh" <rajiv_si...@msn.com> wrote:
> When simulating an estimated model in commandline, use the SIM command
> (look up help on idmodel/sim). For simulation with noise you have two
> options: either specify noise inputs as white noise sequence yourself, or
> simply use the string 'noise' as an input argument to the SIM command. When
> using 'noise' argument, a noise sequence will be genrated automatically.
> This is the simplest thing you can do.
>
> In simulink, use an IDMODEL block to present your model (available as part
> of System Identification Toolbox block library). This block's dialog offers
> an option to add noise to simulation. Note that the model must have a
> disturbance (noise) component in order to use this option. If model('noise')
> comes up empty, then noise cannot be added. All IDPOLY and IDSS models would
> have a noise component by default, even if the noise model is trivial (H=1).
> However, IDPROC model would not have a noise component unless you have
> specifically asked for a disturbance model during estimation (see help on
> idproc and idproc/pem for more info)
>
> Rajiv
>
> "AsimV" <asim...@gmail.com> wrote in message
>
> news:b837280c62f34c0db0323bd17a95f684@x38g2000yqj.googlegroups.com...
>
> > On Feb 24, 6:16 pm, AsimV <asim...@gmail.com> wrote:
> >> On Feb 23, 3:47 pm, "Rajiv Singh" <rajiv_si...@msn.com> wrote:
>
> >> > Your model has one "measured" input and one output. However, there is
> >> > also a
> >> > noise input which you could think of an unmeasured input. When you
> >> > perform
> >> > an estimation, you not only estimate a "measured" model G, but also a
> >> > "noise" model H, according to equation:
>
> >> > y = Gu+He
>
> >> > H is the transfer function between the unmeasured (noise) input e and
> >> > the
> >> > output y. H explains the component of the output that could not be
> >> > captured
> >> > by G. H is also called a disturbance model. The inputs are "u"
> >> > (measured)
> >> > and "e" (unmeasured).
>
> >> > When you do TF(arx221), this operation converts the noise input channel
> >> > (e)
> >> > into a regular input. Hence the number of inputs in the resulting model
> >> > becomes 2. If you just need "G", the transfer function between measured
> >> > input and output, you should do:
>
> >> > g2 = tf(arx221('m'))
>
> >> > This operation separates out the measured component (G) and converts
> >> > only
> >> > that component into a TF object.
>
> >> > HTH,
> >> > Rajiv
>
> >> > "AsimV" <asim...@gmail.com> wrote in message
>
> >> >news:dcb69d15194c40d1acb949000bd8f1c8@l16g2000yqo.googlegroups.com...
>
> >> > > Hello to all,
>
> >> > > I'm experimenting with linear parametric identification methods. I
> >> > > have tested this methods when output data contains noise. I simulated
> >> > > noise by random number generator.
> >> > > Can you please explain to me what does it mean when one gets the
> >> > > following result:
> >> > > g2 = tf(arx221)
>
> >> > > Transfer function from input "u1" to output "y1":
> >> > > 0.4777 z + 0.4677
> >> > > 
> >> > > z^2  0.9353 z  0.01695
>
> >> > > Transfer function from input "v@y1" to output "y1":
> >> > > 0.01454 z^2
> >> > > 
> >> > > z^2  0.9353 z  0.01695
>
> >> > > Data object for identification is formed from one input and one
> >> > > output
> >> > > vector. It is SISO system. How to inperpret input "v@y1" to output
> >> > > "y1"? What does it mean?
>
> >> > > Thank you
>
> >> Thank you Rajiv, you're most helpful.
>
> > Rajiv, I also need help abput simulating noise channel.
> > For example, I have created a model with process data, and I have also
> > "v@y1" part (transfer function) in my model.
> > I'd like to simulate and test the model in the Simulink. It's fairly
> > easy to set up transfer functions blocks with inputs and outputs, but
> > how to simulate that noise part, because I don't know anything about
> > nature of the process noise that is present in the data.
> > Should I use random generator for such such purpose?
>
> > Thanks
Thank you I'll try that.
So far, when I export model to workspace, I use simulink and create
transfer functions form "discrete tools". I just retype numerators and
denomimators from workspace. In the tools "Sources" I can find band
limited withe noise block. Is this the same noise that would be added
by IDMODEL block?
Cheers
