Idmodel
Simulate identified linear model in Simulink software
- Library:
System Identification Toolbox / Models
Description
The Idmodel block simulates the output of an identified linear model
using time-domain input data. The model is a state-space (idss
),
linear grey-box (idgrey
), polynomial (idpoly
),
transfer function (idtf
), or process (idproc
)
model that you previously estimated or created. For the simulation of state-space and
linear grey-box models, you can specify the initial state values. For other linear
models, initial conditions are set to zero. You can also add noise to the simulated
output.
Ports
Input
Port_1(In1)
— Simulation input data
scalar | vector
Simulation input data, specified as a scalar for a single-input model. The data must be time-domain data. For multi-input models, specify the input as an Nu-element vector, where Nu is the number of inputs. For example, you can use a Vector Concatenate (Simulink) block to concatenate scalar signals into a vector signal.
Note
Do not use a Bus Creator (Simulink) or Mux (Simulink) block to produce the vector signal.
Data Types: double
Output
Port_1(Out1)
— Simulated output
scalar | vector
Simulated output from linear model, returned as a scalar for a single-output model and an Ny-element vector for a model with Ny outputs.
Data Types: double
Parameters
Identified model
— Linear model to be simulated
idss(-1,1,1,0,'Ts',1)
(default) | idss
object | idgrey
object | idpoly
object | idtf
object | idproc
object
Initial states (state space only: idss,idgrey)
— Initial state values
0
(default) | vector
Initial state values of state-space (idss
) and linear
grey-box (idgrey
) models, specified as an
Nx-element vector, where Nx is the
number of states of the model. To estimate the initial states that provide a
best fit between measured data and the simulated response of the model for
the same input, use the findstates
command.
For example, to compute initial states such that the response of the model
M
matches the simulated output data in the data set
z
, specify X0
, such that:
X0 = findstates(M,z)
For linear models other than idss
or
idgrey
, the block assumes that initial conditions
are zero.
If
you want to reproduce the simulation results that you get in the Model
Output plot window in the System Identification app, or from the compare
command:
If the identified model
m
is not a state-space or grey-box model, convert the model into state-space form (idss
model), and specify the state-space modelmss
in the block.mss = idss(m);
Compute the initial state values that produce the best fit between the model output and the measured output signal using
findstates
. Specify the prediction horizon asInf
, that is, minimize the simulation error.X0 = findstates(mss,z,Inf);
Use the model
mss
and initial statesX0
in the Idmodel block to perform the simulation. Specify the same input signalz
for simulation that you used as validation data in the app orcompare
.
Add noise
— Add noise to simulated output
on
(default) | off
When you select this parameter, the block derives the noise amplitude from
the linear model property model.NoiseVariance
. The
software filters random Gaussian white noise with the noise transfer
function of the model and adds the resulting noise to the simulated model
response. If you want to add the same noise every time you run the
Simulink® model, specify the Noise seed(s)
property.
For continuous-time models, the ideal variance of the noise term is infinite. In reality, you see a band-limited noise that accounts for the time constants of the system. You can interpret the resulting simulated output as filtered using a lowpass filter with a passband that does not distort the dynamics from the input.
Noise seed(s)
— Add same noise to output for multiple simulations
[]
(default) | nonnegative integer | vector
The Noise seed(s) property seeds the random number
generator such that the block adds the same noise to the simulated output
every time you run the Simulink model. For information about using seeds, see rng
.
For multi-output models, you can use independent noise realizations that generate the outputs with additive noise. Enter a vector of Ny nonnegative integer entries, where Ny is the number of output channels.
For random restarts that vary from one simulation to another, specify
Noise seed(s) as []
.
Dependency
To enable this parameter, select Add
noise
.
Model Examples
Extended Capabilities
C/C++ Code Generation
Generate C and C++ code using Simulink® Coder™.
Version History
Introduced in R2008a
See Also
Functions
Blocks
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