System identification tool and Simulink
3 views (last 30 days)
Show older comments
Hi guys,
i have create some estimation models in the SI Tool. They have a fitness of 94%. Also the fitness ot my validation data is not bad. Like 82%. This is the result of a Hammerstein-Wiener-Model.
No i want this result simulate in Simulink. I use the block for Hammerstein-Wiener-Models, the inputs, and a scope for the output.
Why i get a differ of the simulationresult and SI-Tool result??
Has anyone an idea why the result are not same??
Marcus
0 Comments
Accepted Answer
Arkadiy Turevskiy
on 22 Aug 2012
Edited: Arkadiy Turevskiy
on 22 Aug 2012
Most likely this happens due to initial conditions. In the GUI and in the COMPARE function, the fit is computed by estimating the initial conditions (by default) that maximize the fit to the data. In Simulink, you have to enter the appropriate initial conditions yourself based on your knowledge of the state of the system at the start of the simulation. By default, initial conditions are set to zero in the Simulink block.
See the doc for idnlhw, specifically the section "idnlhw States" for information on how to set initial conditions.
HTH.
Arkadiy
0 Comments
More Answers (1)
Markus
on 24 Aug 2012
1 Comment
Rajiv Singh
on 7 Sep 2012
Initial conditions should not be thought of as a property of the model. It is really the effect of the environment on the initial set up of the model. In a real-life application, you should think about what conditions existed before the model simulation started, or what type of assumptions you can make about them. Some common choices are:
- system at rest (zero)
- system at steady state equilibrium (constant I/o values)
- system at some operating point specified in various ways; use isnlhw/findop to transform your specifications to numerical values of states.
If the goal is to pick initial states that maximize the fit to some measured output signal for a given input signal, then FINDSTATES is your friend.
See Also
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!