User`s guide
4 Nonlinear Black-Box Model Identification
• “Computing Operating P oints at a Simulation Snapshot” on page 4-36
Computing Operating Point from Steady-State Specifications
You can compute an operating point from steady-state specifications, as
follows:
• Using values of input and output signals.
If either the steady-state input or output value is unknown, you can specify
it as
NaN to estimate this value. This is especially useful when modeling
MIMO systems, where o nly a subset of the input and output steady-state
values are known.
• Using m ore complex steady-state specifications.
You construct an object to store the specifications for computing the
operating point, including input and output bounds, known values,
and initial guesses. For more information, see
operspec(idnlarx) or
operspec(idnlhw).
For more information, see the
findop(idnlarx) or findop(idnlhw) reference
page.
Computing Operating Points at a Simulation Snapshot
Youcancomputeanoperatingpointataspecific time during the model
simulation (snapshot). You must spec ify the snapshot time and the input
value for which you want to compute the operating point. If you do not know
the equilibrium values o f s ta t es, you can com pute them us ing an input level
that causes the output level to reach a steady-state after a finite time.
If your system is at steady state and you are working with linear or
Hammerstein-Wiener models, you do not need to specify the initial states
becausetheydonotaffectthesteady-statevalues.FornonlinearARXmodels,
there can be multiple steady states and you should generally specify the
initial states because they can affect steady-state values. By de fa u lt, initial
states are set to zero.
However, if your system ha s n ot reached steady state at the snapshot time,
you must specify the initial states. If you do not know the initial states, you
4-36