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## Vary Uncertainty Values Using Individual Uncertain State Space Blocks

This example shows the workflow for varying uncertainty values using individual Uncertain State Space blocks in a Simulink® model. Use this approach for simple models with few uncertain variables or one Uncertain State Space block.

This section uses a simple Simulink model to provide step-by-step instructions for:

• Toggling between nominal, manually defined and randomly-generated uncertainty values associated with the Uncertain State Space block.

• Simulating the model's responses for these uncertainty values.

1. Open the Simulink model `rct_sim_ex1`.
`rct_sim_ex1`

The model contains an Uncertain State Space block called `Uncertain System`, as shown in the following figure. 2. Double-click the `Uncertain System` block to open the Function Block Parameters dialog box. The `Uncertain System` block uses the uncertain system variable `unc_sys`. This variable is defined in the Model workspace as `unc_sys= ss(ureal('a',-1,'Range',[-2 -.5]),1,5,0)*(1+0.1*input_unc)`. The uncertain model depends on a single uncertain variable named `a`. The Uncertainty value field specifies to use nominal value of the uncertain variable `a`.

Click OK to close the dialog box.

3. Click to simulate the model.

The software uses the nominal value of `a` during simulation. After the simulation completes, the MultiPlot Graph shows the following plot. 4. To simulate the model using a manually defined value of `a`:

1. Double-click the Uncertain State Space block, and enter `struct('a',-0.3)` in the Uncertainty value field. 2. Click to simulate the model.

The MultiPlot Graph shows the following responses, corresponding to the nominal and manually-defined values of `a`. 5. Pick a random value of `a` in its uncertainty range. To do so, double-click the Uncertain State Space block, and type `usample(ufind(unc_sys))` in the Uncertainty value field. 6. Analyze the uncertainty effects by simulating the model ten times using the following commands:

```for i=1:10; sim('rct_sim_ex1',10); end```

During simulation, the software samples the uncertain variable `a` in its uncertainty range [-2 -0.5] and shows the simulated response for each sample value. The plots cycle through seven different colors, and the last response appears in red. Tip: You can clear the plots in the MultiPlot Graph block before you run the simulation. 