As described in Specify Uncertainty Using Uncertain State Space Blocks, the uncertain
state-space model you specify in the Uncertain State Space block depends on a set of
uncertain variables (
ultidyn objects.) You can simulate the model
using nominal value of these uncertain variables. Additionally, you can sample these
uncertain variables and simulate the model for various values in the uncertainty range
(Monte Carlo simulation.) For more information, see How to Vary Uncertainty Values. You can view and
compare the simulation results for various sample values of uncertainty using the MultiPlot Graph block.
There are two ways to control the uncertainty values using the Uncertainty value (struct or  to use nominal value) field of the Uncertain State Space block parameters dialog box:
For simple models with few uncertain variables or one Uncertain State Space block, type the value in the Uncertain State Space block itself. For more information, see Simulate Uncertain Model at Sampled Parameter Values.
For complex models with large number of uncertain variables or Uncertain State Space blocks, use a single data structure for all uncertain variables referenced by the model. Using this approach, you can collectively control the values of all or a subset of uncertain variables and toggle between nominal and user-defined values from the MATLAB® prompt. For more information, see Vary Uncertain Values Across Multiple Uncertain Blocks.