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Variant Control Mode in Variant Parameters

The components of a Simulink® model that contain variants are activated or deactivated based on the variant choice that you select.

Each variant choice in your model is associated with a variant control. Variant controls determine which variant choice is active. By changing the value of a variant control, you can switch the active variant choice. While each variant choice is associated with a variant control, only one variant control can evaluate to true. When a variant control evaluates to true, Simulink activates the variant choice that corresponds to that variant control. For a simple example, see Introduction to Variant Controls.

Switch Between Choices Using Condition Expressions in Variant Parameters

In expression mode, Simulink chooses the active variant based on the evaluation of the variant conditions. When a condition expression evaluates to true, the corresponding variant choice becomes active. When a condition expression evaluates to false, the corresponding variant choice becomes inactive.

Note

You can simulate and generate code from the model containing a variant parameter with Variant control mode set to expression mode. The generated code can contain active and inactive choices that are enclosed in preprocessor conditionals #if and #elif, or regular if conditions.

With expression type of variant control mode:

Use expression Type of Variant Controls in Variant Parameters

To specify the variant condition expressions in variant parameters, use the Simulink.VariantVariable object. Once you successfully create the Simulink.VariantVariable objects, you can modify them by using the methods described in Public Methods or from the VariantVariable dialog box. For more information, see Create a Simple Variant Parameter Model.

K1 = Simulink.VariantVariable('Choices', {'VSS_MODE == 1', 3.5, 'VSS_MODE == 2', 8.5})

Types of Variant Controls in expression Mode

In variant parameters, the expression type of variant controls can be:

Here, A and B are operands called as variant control variables. ==, ~=, and && are operators in the condition expression. The condition expression can contain one or more such variant control variables and operators. For information on supported types and storage location of variant control variables, see Types of Variant Control Variables (Operands) in Variant Parameters and Storage Locations for Variant Control Variables (Operands) in Variant Parameters. For information on operators, see Types of Operators in Variant Parameters.

Types of Variant Control Variables (Operands) in Variant Parameters

In expression mode, you can specify the variant control variables as any of these types, from options to use while prototyping to options required for generating code from your model.

SpecificationPurposeExample
Simulink.VariantControl objectAssociate a variant activation time

V = Simulink.VariantControl(Value=1,ActivationTime="code compile")
See Numeric Variant Control Values for Rapid Prototyping of Variant Parameters.

Simulink.Parameter objectGenerate preprocessor conditionals for code generation

VSS_MODE = Simulink.Parameter(1);
V = Simulink.VariantControl(Value=copy(VSS_MODE),ActivationTime="code compile")
where VSS_MODE is a Simulink.Parameter object. See Simulink.Parameter Type of Variant Control Variables for Code Generation of Variant Parameters.

User-defined data class object

Use custom type that inherits from Simulink.Parameter as value of Simulink.VariantControl

Custom Data Class Objects as Values of Simulink.VariantControl Objects
Simulink EnumerationsImproved code readability because condition values are represented as meaningful names instead of integers

V = Simulink.VariantControl(Value=EngType.Small,ActivationTime="code compile")
where EngType is an integer-based enumeration class and Small is the enumerated value. See Enumerated Types to Improve Code Readability of Variant Control Variables of Variant Parameters.

Simulink.Variant objectReuse variant conditions

V = Simulink.VariantControl(Value=1,ActivationTime="update diagram");
LinearController=Simulink.VariantExpression("V==1");
NonLinearController=Simulink.VariantExpression("V==2");
K1 = Simulink.VariantVariable('Choices',{'LinearController',3.5,'NonLinearController',8.5});
where LinearController and NonLinearController are Simulink.VariantExpression objects used to encapsulate variant conditions. See Simulink.VariantExpression Objects for Variant Condition Reuse of Variant Parameters.

For list of all examples, see Use Variant Control Variables in Variant Parameters.

Storage Locations for Variant Control Variables (Operands) in Variant Parameters

You can define the variant control variables in different storage locations based on your requirement.

Note

All the variant control variables in a variant parameter must originate from the same storage location.

Storage LocationUse for Storage LocationSupported Types of Variant Control Variables (See Types of Variant Control Variables (Operands) in Variant Parameters)For More Information
Base workspaceStore variables while you experiment with temporary models Simulink.VariantExpression, Simulink.Parameter, enumerated type, and Simulink.VariantControlTemporary Data: Base Workspace
Data dictionaryPermanently store global data, share data between models, and track changes made to data.Simulink.VariantExpression, Simulink.Parameter, enumerated type, and Simulink.VariantControlWhat Is a Data Dictionary?

For capabilities and advantages of each storage location, see Determine Where to Store Variables and Objects for Simulink Models.

Types of Operators in Variant Parameters

Variant condition expressions can contain MATLAB® operators, provided the expression evaluates to a boolean value. In variant parameters, the operators that you can use to form a variant condition expression are:

  • Parentheses for grouping

  • Relational Operators and Logical Operators as listed in this table.

    This table lists the supported MATLAB operators and their equivalent in the generated code. In these examples, A and B are expressions that evaluate to an integer.

    Supported MATLAB ExpressionsEquivalent Expression in Generated C Code
    Relational

    A == B

    		A == B

    A ~= B

    		A != B
    Logical
    ~A!A, where A is not an integer
    A && BA && B
    A || BA || B

Evaluate Variant Condition Expressions at Different Variant Activation Times

In expression mode, you can specify if Simulink must evaluate condition expressions during model compile, simulation-loop, code compile, or model start up stage of simulation and code generation workflow using variant activation times. For information on stages of simulation and code generation, and supported variant activation times in expression mode, see Activate Variant During Different Stages of Simulation and Code Generation Workflow.

Variant Activation Times for Different Variant Control Modes in Variant Parameters

This table explains the variant activation time supported for different variant control modes in variant parameters. For information on variant activation times, see Activate Variant During Different Stages of Simulation and Code Generation Workflow.

Variant control modeVariant activation time
 update diagramupdate diagram analyze all choicescode compilestartupruntime(Variant Subsystem block only)
expression✓✓✓✓✓
labelnot supportednot supported
sim codegen switchingnot supportednot supported

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