How can I set nonlinear constraints in a nonlinear grey-box model?

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Philipp Smilgies
Philipp Smilgies 2018-1-22
回答： Rajiv Singh 2022-9-23
Hi,
I´m estimating pramaters of a nonlinear state-space model with the System Identification Toolbox and the function nlgreyest.
Is it possible to add nonlinear constraints to the estimation?
For example:
One equation of my state-space model is
dx(1) = K1*x(1) + K2*x(2) + K3*u(1);
And now I want to add a nonlinear constraint like this to the estimation.
0.5 = K1 / (2*sqrt(K2));
Can someone help me solve this problem?
Thanks, Philipp

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回答（1 个）

Rajiv Singh
Rajiv Singh 2022-9-23
Linear or nonlinear constraints are not supported in nlgreyest directly. Depending upon the problem, you can sometimes get away with a re-parameterization, and.or simple min/max bounds. For example in the example you have given, you can eliminate K1 by replacing it with sqrt(K2), and a lower bound K2>0.

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