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USS System

Import uncertain systems into Simulink


USS System block will be removed in a future release. Use Uncertain State Space block instead.


The USS System block accepts USS and UMAT containing ureal and ultidyn uncertain objects, as well as ureal and ultidyn objects. An instance of the uncertain system is used in the simulation or linearization. Internally, USS models are converted to their state space equivalent for evaluation.


USS system variable

The uncertain object (USS, UMAT, ureal, or ultidyn) is entered in the USS system variable.

Initial states (nominal dynamics)

If the nominal value for the USS system variable has states, then the initial condition for these states is entered in Initial states (nominal dynamics).

Uncertainty value

The values for the uncertain elements are controlled by the Uncertainty value menu. If Nominal is selected, then the nominal value of the uncertain object is used. If you select User defined, then you must enter a MATLAB® structure in the User-defined uncertainty (struct) dialog box. The field names of the structure should correspond to the names of the uncertain atoms within the USS system variable, while the values of the fields are the values used for the uncertain objects (using the command usubs). If some of these values are SS objects, then these states are referred to as uncertainty states.

The order of the uncertainty states is determined by the order of atoms in the Uncertainty property of the USS system variable. The state dimension is determined by the actual data in the User-defined uncertainty structure. Any extra fields in the User-defined uncertainty structure are ignored.

User-defined uncertainty (struc)

If User defined is selected from the Uncertainty value pop-up menu, then the structure data entered in User-defined uncertainty (struct) must contain fields corresponding to every uncertain atom of the USS system variable. Extra fields are ignored. usimsamp generates a random instance of each atom in a Simulink® model. It returns a structure, suitable for entry in User-defined uncertainty (struct).

Initial states (uncertain dynamics)

The initial condition for the uncertainty states is entered in Initial states (uncertain dynamics).

Introduced in R2007a

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