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. See Switch Between Choices Using Condition Expressions in Variant Parameters.

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 code compile activation time to generate a code that contains active and inactive choices of the model in C preprocessor conditionals #if and #elif. The preprocessor conditionals are conditionally compiled for the active choice that you provide as an input to the compiler. For more information, see Compile Code Conditionally for all Values of Variant Parameters with Same and Different Dimensions.
Use startup activation time to:
- Improve the speed of iterative simulations and Simulink Test™ workflows using fast restart. For more information, see Run Iterative Simulations Without Recompiling Model for Variant Systems Using Fast Restart.
- Generate a code that contains active and inactive choices of the model in regular if conditions. The if condition is evaluated and conditionally executed for the active choice that you provide as an input to the executable. For more information, see Run Executable for Different Variant Parameter Values Without Recompiling Code.

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:

Boolean condition expression for rapid prototyping. For example, A == 1, A ~= B, A && B == 1, and so on.
A Simulink.Variant object that contains a condition expression for condition reuse. See Simulink.Variant Objects for Variant Condition Reuse of Variant Parameters.

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.

Specification	Purpose	Example
`Simulink.VariantControl`	Associate a variant activation time	`A == 1`, where `A` is a `Simulink.VariantControl` object. See Numeric Variant Control Values for Rapid Prototyping of Variant Parameters.
`Simulink.Parameter` object	Generate preprocessor conditionals for code generation	`Vssmode == 1`, where `Vssmode` is a `Simulink.Parameter` object. See Simulink.Parameter Type of Variant Control Variables for Code Generation of Variant Parameters.
Simulink Enumerations	Improved code readability because condition values are represented as meaningful names instead of integers	`LEVEL == Level.Advanced`, where `Level` is an integer-based enumeration class and `Advanced` is the enumerated value. See Enumerated Types to Improve Code Readability of Variant Control Variables of Variant Parameters.
`Simulink.Variant` object	Reuse variant conditions	`LinearController == 1`, where `LinearController` is a `Simulink.Variant` object that encapsulates the condition expression `FUEL==2 && EMIS==1`. See Simulink.Variant 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 Location	Use for Storage Location	Supported Types of Variant Control Variables (See Types of Variant Control Variables (Operands) in Variant Parameters)	For More Information
Base workspace	Store variables while you experiment with temporary models	`Simulink.Variant`, `Simulink.Parameter`, enumerated type, and `Simulink.VariantControl`	Temporary Data: Base Workspace
Data dictionary	Permanently store global data, share data between models, and track changes made to data.	`Simulink.Variant`, `Simulink.Parameter`, enumerated type, and `Simulink.VariantControl`	What 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 Expressions Equivalent Expression in Generated C Code
Relational
A == B
A == B
A ~= B
A != B
Logical
~A !A, where A is not an integer
A && B A && B
A || B A || B

Supported MATLAB Expressions	Equivalent Expression in Generated C Code
Relational
`A == B`	`A == B`
`A ~= B`	`A != B`
Logical
`~A`	`!A`, where `A` is not an integer
`A && B`	`A && B`
`A \|\| B`	`A \|\| 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 mode	Variant activation time
	`update diagram`	`update diagram analyze all choices`	`code compile`	`startup`
`expression`	✓	✓	✓	✓
`label`	not supported
`sim codegen switching`	not supported