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Compute operating point for Hammerstein-Wiener model
[X,U] = findop(SYS,'steady',InputLevel,OutputLevel)
[X,U] = findop(SYS,SPEC)
[X,U] = findop(SYS,'snapshot',T,UIN,X0)
[X,U,REPORT] = findop(...)
findop(SYS,...,PVPairs)
[X,U] = findop(SYS,'steady',InputLevel,OutputLevel) computes operating-point state values, X, and input values, U, from steady-state specifications for an idnlhw model. For more information about the states of an idnlhw model, see idnlhw States.
[X,U] = findop(SYS,SPEC) computes the equilibrium operating point using the specifications in the object SPEC. Whereas the previous command only lets you specify the input and output level, SPEC provides additional specification for computing the steady-state operating point.
[X,U] = findop(SYS,'snapshot',T,UIN,X0) computes the operating point at a simulation snapshot of time T using the specified input and initial state values.
[X,U,REPORT] = findop(...) creates a structure, REPORT, containing information about the algorithm for computing an operating point.
findop(SYS,...,PVPairs) specifies property-value pairs for setting algorithm options.
SYS: idnlhw (Hammerstein-Wiener) model.
'steady': Computes operating point using steady-state input and output levels.
'snapshot': Computes operating point at simulating snapshot of model SYS at time T.
InputLevel: Steady-state input level for computing operating point. Use NaN when the value is unknown. Do not enter OutputLevel when InputLevel does not contain any NaN values.
OutputLevel: Steady-state output level for computing the operating point. Use NaN when the value is unknown.
SPEC: Operating point specifications object. Use SPEC = OPERSPEC(SYS) to construct the SPEC object for model SYS. Then, configure SPEC options, such as signal bounds, known values, and initial guesses. See operspec(idnlhw) for more information.
T: Simulation snapshot time at which to compute the operating point.
UIN: Input for simulating the model. UIN is a double matrix or an iddata object. The number of input channels in UIN must match the number of SYS inputs.
X0: Initial states for model simulation.
Default: Zero.
PVPairs: Property-value pairs for customizing the model Algorithm property fields, such as SearchMethod, MaxSize, and Tolerance.
X: Operating point state values.
U: Operating point input value.
REPORT: Structure containing the following fields:
SearchMethod: String indicating the value of the SearchMethod property of MODEL.Algorithm.
WhyStop: String describing why the estimation stopped.
Iterations: Number of estimation iterations.
FinalCost: Final value of the sum of squared errors that the algorithm minimizes.
FirstOrderOptimality: Measure of the gradient of the search direction at the final parameter values when the search algorithm terminates. It is equal to the $$\infty $$-norm of the gradient vector.
SignalLevels: Structure containing fields Input and Output, which are the input and output signal levels of the operating point.
In this example, you compute the operating point of an idnlhw model for a steady-state input level of 1.
Estimate an idnlhw model from sample data iddata2.
load iddata2; M = nlhw(z2,[4 3 2],'wavenet','pwl');
Compute the steady-state operating point for an input level of 1.
x0 = findop(M,'steady',1,NaN)