Initial Conditions

Specify initial conditions for the system under Systems. To see the choices, click the entry under Initial Conditions. You can select one of the following options.

• Estimate — Estimate initial conditions such that the prediction error for observed output is minimized.

• Zero — Zero initial conditions.

• Absorb Delays and Estimate — Similar to Estimate, but this option also absorbs nonzero delays into the model coefficients. The software converts delays into explicit model states, and estimates and returns the initial values of those states.

  Use this option for linear models only.

• Custom — Specify the initial conditions. Use this option when you already know or have an estimate for the initial conditions. Specify a column vector of length equal to the order of the model.

For nonlinear grey-box models, when you select Estimate, the software estimates only those initial states i that are designated as free in the model, as indicated by the property sys.InitialStates(i).Fixed equal to false. To estimate all the states of the model, first specify all the Nx states of the idnlgrey model sys as free.

for i = 1:Nx
sys.InitialStates(i).Fixed = false;
end 

Similarly, to fix all the initial states to values specified in sys.InitialStates, first specify all the states as fixed in the sys.InitialStates property of the nonlinear grey-box model.

When you have completed your selection, regenerate the response plot by clicking Simulate.