When you have the Simulink® Control Design™ software, you can compute an uncertain linearization, i.e., an uncertain state-space model (uss) combining the uncertain variables with linearized dynamics. Use the uss model to perform linear analysis and robust control design.
You can compute an uncertain linearization in one of the following ways:
Using the ulinearize command, as described in Obtain Uncertain State-Space Model from Simulink Model.
Using the Simulink Control Design linearize command, as described in Specify Uncertain Linearization for Core or Custom Simulink Blocks.