Specify Design Variables
This topic shows how to specify design variables for optimization.
Before running the optimization, you must specify the model parameters to optimize. These parameters form the design variables set for optimization. By tuning these parameters, Simulink® Design Optimization™ software attempts to make the signals meet the requirements. Simulink Design Optimization software optimizes the response signals of the model by varying the tuned parameters so that the response signals lie within the constraint bound segments or closely match a specified reference signal. The design variables can be scalar, vector, matrix, or an expression that evaluates to one of these values.
You can also use sensitivity analysis for finding the parameters that most influence the optimization problem and use these as design variables. To open the Sensitivity Analyzer, in the Response Optimization tab, click Sensitivity Analysis. In the Sensitivity Analyzer app, you can explore the response optimization design space by altering the design variables, identify the parameters that most influence the optimization problem, and compute initial values.
Add Model Parameters as Variables for Optimization
The software can only optimize variables that are in use by the Simulink model. Create variables for optimization in the MATLAB® or model workspace, and specify your model or block parameters using these variables.
In this figure, the Proportional (P) and Integral (I) gain parameters of a PID Controller block are specified as numerical values.
To optimize the gain parameters, specify them as variables
Create the variables
Kiin one of the following ways:
Specify the gain parameters as the variables
Kiin the PID Controller block dialog box.
You can now select
optimization. See, Specify Design Variables.
Specify Design Variables
To specify the parameters to be tuned using the Response Optimizer:
In the Design Variables Set list, select New.
A window opens where you specify design variables. All parameters in use by the model are displayed in this window.
Select one or more parameter names and click
to add the selected parameters to a design variables set.
You can add the same parameter to multiple design variable sets.
(Optional) Specify design variable settings.
Setting Description Default
The name of the parameter.
Not an editable field
Value of the model parameter. This value is used by the optimization method as the initial value and is modified during optimization.
Current value of the parameter in the model. If you edit this column, click Update model variable values to update the values in the model.
The minimum value or lower bound for the parameter. You can edit this field to provide an alternate minimum value.
The maximum value or upper bound for the parameter. You can edit this field to provide an alternate maximum value.
During optimization, the design variables are scaled, or normalized, by dividing their current value by a scale value. You can edit this field to provide an alternate scaling factor.
Next power of 2 greater than the current value of the parameter
The check-box indicates whether the parameter is selected as a design variable in the set. Select it if you want this parameter to be tuned during the optimization. Deselect if you do not want this parameter to be tuned during the optimization but you would like to keep it on the list of tuned parameters (for a subsequent optimization).
Expand Variable Detail to see the block in the model that contains this parameter.
Click OK to create a design variable set.
If your model contains referenced models, you can
select the referenced variables from the Create Design Variables
Set dialog box. For example, the first variable in the dialog box,
Slew, is listed as
sdoRateLimitedController is the name of the referenced model
with the variable
Slew variable has
the same value for all instances of the
model. In contrast, the variable
Kd can have a different value
for each instance of the referenced model containing it. For example, the second
variable in the dialog box is listed as
sdoMultipleMotors/Control_1:Kd. The upper-level model
sdoMultipleMotors has block
which is a referenced model that has variable
Kd. The value of
this variable can be different than
Kd in block
Control_2, which is the third variable in the dialog box. To
enable instance-specific values,
Kd is specified as a model
argument in the referenced model workspace.