Nonlinear System Identification | System Identification, Part 3

Learn about nonlinear system identification by walking through one of the many possible model options: A nonlinear ARX model.

Brian Douglas covers the importance of adding an offset term to a linear model, adding nonlinear elements to the regressor vector, and adding a nonlinear combination of regressors.

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[jennariseley]

This is awesome, using intuition from the physical system to improve the model is just amazing

[betting]

he calls himself Brian, we call him GOAT

[michacukrowski]

Damn one of the first NAR videos online. Thanks!

[ft]

System identification is very close to magic.

[khaledsaleh]

Thank you, please provide link to the estimation and validation data used in the video. Please note the 'linearRegressor' is not defined in Matlab R2018b.. please advise.

[hassanalihassan]

great video! and a smooth introduction to NARX models... can you give us some insights about the sufficient richness and persistent excitation of input data to generate a good dataset to train the model?

[gabrielbrunheira]

Great stuff as usual! Regarding knowledge about the system that can be used, I was wondering whether a saturation (non-linear) function of the output could also be used by these methods, to address in a natural way the limits of the tank (full or empty), for example. It seems that the sigmoid function kind of captures this in a more behaved fashion (continuous function) either way.

[oussamasadki]

Thanks for the very planned-out videos you post.
I have a miss understanding of a point you rush through it a bit, stability issues of nonlinear systems when predicting output? Why is that occuring? Apart from the external input sequences the system has never seen before.
Thanks.

[annabaasch]

Hi Brian Douglas, your videos helped me a lot. I'm modeling a very slow first order thermal system, but working close to 1200ºC, passing through the specific temperature of a test piece, which I imagine is a disturbance, at least that's what I've seen in the residual graphics. Any advice to achieve a reliable model in this case? Anyway thank you so much for the videos.

[luiggitello]

I have a question. You sair linear models cant handle the offset. However the start point is the initial conditions, and linear models can be initialized at any x0. How is this distintion made in the software?

[IvayloGan]

Can you give a link to this example to play around with it

[necunoscut]

does anybody else have the following issue: Unrecognized function or variable 'idWaveletNetwork'. ? any ideas what to do about it? i've installed deep learning and system identification toolboxes, but it's not it.

would be great if the next video was about nonlinear system identification for MIMO systems

[Fihaa]

Hello Brian, first let me congratulate you for this amazing video, just one question; i am using matlab 2023 and still linearRegressor output the following error: Error using idRegressorSpec/set.Lags
The value of the "Lags" argument must be a cell array of unique non-negative index vectors, one vector for each variable.

[dominikz]

Does anyone have experience with identifing friction in elektro-mechanical systems? I excited my elektro-mechanical system with PRBS as input (current) and recorded the output (velocity). Now i want to identify a model that captures the nonlinearity of the mechanical friction. Any tips?

[michTech]

cool 😁 i thought arx describes the error model H=1/A (y=B/A u + 1/A e)?

[aminaboulbadaoui]

but why you're not using sys identification that exists on matlab toolbox and then u just choose the transfert function that gives u the best fit ?

[learnenglishwithmovie]

excellent video . I really appreciate it.


THANK

[Qaidi_]

How can we use Bode Plot to identify our Black Box system?