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What Are Variants and When to Use Them

What Are Variants?

In Model-Based Design workflows, creating multiple design variations for system components is essential to meet different sets of requirements. These requirements can cater to diverse market needs, customer preferences, or geographical features. Throughout the development lifecycle, from requirements to deployment, you may need to switch between these design choices.

Simulink^® variant capabilities allow you to represent all design alternatives of a system in a single model. Each design choice is incorporated into the model as a variant choice. Such models have a fixed common structure and a finite set of variable components that are activated depending on the variant choice. This model shows how Variant Source blocks help you implement variant choices for the input signals to a system. The inactive choice appears faded.

For an example, see Use Variants to Create One Model for Many Systems.

Variable and fixed components in a model

Advantages of Using Variants

Using variants in Model-Based Design provides several advantages:

Variants allow you to design one model for many systems.
You can rapidly prototype design possibilities as variants without having to comment out sections of your model.
Variants help you develop modular design platforms for reuse and customization. This approach improves workflow speed by reducing complexity.
If a model component has several alternative configurations, you can explore the alternatives without altering the fixed components.
You can use different variant configurations for simulation or code generation from the same model.
You can simulate every design possibility for a given test suite.
If you are working with large-scale designs, you can distribute the process of testing these designs on a cluster of multicore computers. Alternatively, you can map different test suites to design alternatives for efficient management of design-specific tests.
You can generate a reduced model for a subset of variant configurations from a model with many variants.

When to Use Variants

Here are three scenarios where you can use variants.

Models that represent multiple simulation, code generation, or testing workflows.
Models that contain multiple design choices at the component level.
Models that are mostly similar but have slight variations, such as in cases where you want to separate a test model from a debugging model. The test model on the left has a fixed design. On the right, the same test model includes a variant that is introduced for debugging purposes.

Types of Variants in Simulink

Variant blocks help you represent multiple structural or algorithmic implementations of a system component in a single model and allow you to switch between them as per requirements. For an overview of the types of variant blocks in Simulink, see Variant Blocks in Simulink.

Variant parameters help you implement design variations that require varying values for block parameters. For more information, see Use Variant Parameters to Reuse Block Parameters with Different Values.

Variant transitions allow you to transition to multiple design configurations within the same Stateflow^® chart. For more information, see Control Indicator Lamp Dimmer Using Variant Conditions (Stateflow).

Dimension variants allow you to specify symbolic dimensions that vary based on variant conditions. See Implement Symbolic Dimensions for Array Sizes in Generated Code (Embedded Coder).

AUTOSAR variants enable you to use variant blocks to implement AUTOSAR software components with variation points. See Model AUTOSAR Variants (AUTOSAR Blockset).

Tip

For a list of examples that show variant capabilities in Simulink, see V-Model for System Development with Simulink Variants.

To see definitions for key terms and parameters used with variants, see Variant Terminology.

For examples that show variant code generation capabilities, see Variant Systems (Embedded Coder).

Variant Blocks in Simulink

Use these variant blocks depending on the model design:

Hierarchical variant blocks to create multiple implementations of a component in a separate hierarchy in the model.
Inline variant blocks to represent all variant implementations at the same level in the model.
Event-based variants to use variants to model context-dependent system behaviors.

Type of Variant	Variant Block	Use
Hierarchical variant blocks	Variant Subsystem	The Variant Subsystem block is a template preconfigured with Subsystem blocks to represent the variant choices. The Variant Subsystem block allows a combination of Subsystem blocks, Model blocks, or Subsystem Reference blocks as variant choices.
	Variant Model	The Variant Model block is a template preconfigured with two Model blocks to represent the variant choices. The Variant Model block allows a combination of Subsystem blocks, Model blocks, or Subsystem Reference blocks as variant choices.
	Variant Assembly Subsystem	The Variant Assembly Subsystem block enables you to add or remove its variant choices from external files. The Variant Assembly Subsystem allows a combination of Model blocks, or Subsystem Reference blocks as variant choices.
Inline variant blocks	Variant Source	The Variant Source block allows you to define variant choices as block regions connected to each of its inports. The block provides variation on the source of a signal.
	Variant Sink	The Variant Sink block allows you to define variant choices as block regions connected to each of its outports. The block provides variation on the destination of a signal.
	Manual Variant Source	The Manual Variant Source block is a toggle switch that allows you to define multiple variant choices at its inports.
	Manual Variant Sink	The Manual Variant Sink block is a toggle switch that allows you to define multiple variant choices at its outports.
	Variant Connector (Simscape)	The Variant Connector block lets you define variant choices in a physical network. You can switch between components in the network during simulation without having to physically remove the components or exclude them from simulation.
Event-based variants	Simulink Function	The variant functionality in the Simulink Function block allows the block to be conditionally available. You can specify variant conditions on the function call port block or the block can inherit the condition from its function caller blocks.
Event-based variants	Initialize Function, Reset Function, and Terminate Function blocks	The variant functionality in Initialize, Reset, and Terminate blocks allow the blocks to be conditionally available. You can specify variant conditions on the event listener block.

Compare Variant Blocks

This table presents a comparison between hierarchical and inline variant blocks.

Feature	Variant Source and Variant Sink blocks	Variant Subsystem and Variant Model blocks
Variant choice representation	Number of ports	Subsystem, Model, or Subsystem Reference blocks
Allows to implement variant choices in a separate hierarchy	No	Yes
Supports flexible number of inputs and outputs among variant choices (the choices do not have similar interface)	No	Yes, if the Propagate conditions outside of variant subsystem parameter is set to `on`.
Option to specify default variant	Yes	Yes
Supports control ports	No	Yes
Can be saved as standalone file	No	No
Supports Connection Port used for modeling physical connection lines	No	Only when the Variant activation time parameter is set to `update diagram`.
Comment a variant choice (by adding the `%` symbol before the variant control in the Block Parameters dialog box)	No	Yes

Use Variants to Create One Model for Many Systems

This example shows variant design in a Simulink model. Consider the requirement to model a system that represents an automobile with several configurations. These configurations, although similar in several aspects, can differ in properties such as fuel consumption, motor type, or emission standard.

Automobile configurations with different properties

Instead of designing separate models for each configuration, you can represent the configurations as variant choices in a single model. You can choose to activate any one of the variant choices based on your requirements. This approach keeps the common components fixed.

This model contains a Variant Subsystem block, Motor Variant Subsystem, that represents the motor of the vehicle. The motor has two possible configurations, Gas and Electric, that are represented as variant choices within the Variant Subsystem block. A Variant Subsystem block adapts its interface according to the state of the underlying blocks. Here, the Electric motor does not have an exhaust temperature input. When you activate the Electric variant, Simulink automatically disables the corresponding port on the Motor Variant Subsystem and any other model components associated with that input.

For the exhaust temperature sensor for this model, consider the need to switch between five different sensors provided by two vendors. You can use Variant Source blocks to represent all the choices in the same model and activate only one choice at a time.

Variant Source blocks used to select a sensor

Working with Variants

Visual Elements in Variant Models

Visual Element	Use
Variant Condition Legend	The Variant Condition Legend dialog box helps you visualize the variant conditions applied on the model. Simulink annotates model components that have variant conditions, and the Variant Condition Legend displays the conditions for each annotation. See Visualize Propagated Variant Conditions in Variant Conditions Legend.
Variant Badges	Each variant block displays a badge that changes with different parameter values set on the block. See Variant Badges.
Variant Fading and Signal Highlighting	The color of inactive variant choices fades by default. You can choose to disable the fading effect by using the Variant Fading option in the Information Overlays menu on the Debug tab of the Simulink Editor. Highlighting a signal that passes through variant blocks highlights the path of the active variant choice. See Signal Highlighting in Variant Systems.

Visual Element

Use

Variant Condition Legend

The Variant Condition Legend dialog box helps you visualize the variant conditions applied on the model. Simulink annotates model components that have variant conditions, and the Variant Condition Legend displays the conditions for each annotation. See Visualize Propagated Variant Conditions in Variant Conditions Legend.

variant condition legend

Variant Badges

Each variant block displays a badge that changes with different parameter values set on the block. See Variant Badges.

Variant Fading and Signal Highlighting

The color of inactive variant choices fades by default. You can choose to disable the fading effect by using the Variant Fading option in the Information Overlays menu on the Debug tab of the Simulink Editor.

Highlighting a signal that passes through variant blocks highlights the path of the active variant choice. See Signal Highlighting in Variant Systems.

Signal highlighting in variant model

Variant Badges

Each variant block displays a badge. The color and icon of the variant badge changes according to values of these parameters set on the block:

Variant activation time
Variant control mode
Allow zero active variant controls (for Variant Source and Variant Sink blocks)
Propagate conditions outside of variant subsystem (for Variant Subsystem block)

Variant Badges also provide quick access to some variant commands. Right-click the variant badge to access these commands.

Note

The Refresh Blocks (Ctrl+K) option on the variant badge does not re-evaluate the variables that are defined in the mask workspace of the variant blocks. For example, consider a masked Variant Subsystem block with the variant control variable defined in the mask workspace of the block. To change the active choice of the block, you change the value of the variant control variable. When you then click the Refresh Blocks (Ctrl+K) option, the variant control variable is not re-evaluated and so the active choice of the block is not updated. You must click Apply on the mask dialog or update the diagram for the latest active choice to reflect.

Variant Badge Icons for Different Settings on Variant Blocks

Variant Badge

Variant Source

Variant Sink

Variant Subsystem

Default Variant badge when no option is selected.

Variant block with Label selected as Variant control mode and an active variant choice is selected from Label mode active choice option.

Variant block with Allow zero active variant controls option selected.

Variant block with expression selected as Variant control mode and update diagram selected as Variant activation time.

Variant block with expression selected as Variant control mode and update diagram analyze all choices selected as Variant activation time.

Variant block with expression selected as Variant control mode and code compile selected as Variant activation time.

Variant block with expression selected as Variant control mode and startup selected as Variant activation time.

Variant block with sim codegen switching selected as Variant control mode and update diagram selected as Variant activation time.

Variant block with sim codegen switching selected as Variant control mode and update diagram analyze all choices selected as Variant activation time.

Variant block with Propagate conditions outside of variant subsystem option selected.

Not applicable

Variant block with

update
                                            diagram

selected as Variant activation time and Allow zero active variant controls option selected.

Variant block with

update diagram analyze
                                            all choices

selected as Variant activation time and Allow zero active variant controls option selected.

Variant block with

code
                                            compile

selected as Variant activation time and Allow zero active variant controls option selected.

Variant block with startup selected as Variant activation time and Allow zero active variant controls option selected.

Variant block with

inherit from
                                            Simulink.VariantControl

selected as Variant activation time before model compile.

Variant block with

update
                                            diagram

selected as Variant activation time and Propagate conditions outside of variant subsystem option selected.

Not applicable

Variant block with

update diagram analyze
                                            all choices

selected as Variant activation time and Propagate conditions outside of variant subsystem option selected.

Not applicable

Variant block with

code
                                            compile

selected as Variant activation time and Propagate conditions outside of variant subsystem option selected.

Not applicable

Variant block with startup selected as Variant activation time and Propagate conditions outside of variant subsystem option selected.

Not applicable

Variant block with Allow zero active variant controls and Propagate conditions outside of variant subsystem option selected.

Not applicable

Variant block with sim codegen switching selected as Variant control mode and Propagate conditions outside of variant subsystem option selected.

Not applicable

Define and Control Variant Choices

You must associate each variant choice in a model with a variant control that is used to determine if the choice is active or inactive. For variant blocks, you can choose the mode in which you want to specify the variant controls using the Variant control mode parameter. For more information, see Introduction to Variant Controls.

Variant control mode and variant activation time in the block parameters dialog box

Automatically Identify Variant Regions Using Variant Condition Propagation

Simulink determines the model components that are active during simulation by the process of variant condition propagation. This process evaluates the variant controls specified on the variant blocks and automatically propagates the variant conditions to the connecting blocks. Variant conditions can propagate through signal lines, buses, and function calls. The process deactivates the model components associated with the inactive choices and they are not included in simulation. You can stop condition propagation to define variant regions in the model. See Propagate Variant Conditions to Define Variant Regions with Variant Blocks.

Variant condition propagation

Choose a Variant Activation Time

You can also choose when the active variant choice is determined using the Variant activation time parameter. This parameter also determines how the active and inactive choices participate in the simulation and code generation workflows. See Activate Variant During Different Stages of Simulation and Code Generation Workflow.

Note

You can choose the variant activation time for a variant block only when Variant control mode is set to expression.

Manual Variant Source and Manual Variant Sink blocks do not support variant controls and variant activation time. They determine the active variant choice based on the active inports and outports, respectively.

Variant Connector blocks do not support variant activation time.

Manage All Variants Using Variant Manager

Variant Manager is a tool that allows you to visualize the model hierarchy and centrally manage the usage of variant elements across the hierarchy.

The tool is available as a support package named Variant Manager for Simulink with these main capabilities:

Variant Manager — Visualize the model hierarchy, manage the usage of variant elements across the hierarchy, create and manage variant configurations.
Variant Reducer — Generate a reduced model that contains only selected variant configurations.
Variant Analyzer — Compare and contrast variant configurations to identify errors or inconsistencies.

Create and Activate Variant Configurations:

A model hierarchy may contain several variant blocks, each with many variant choices. Combinations of these variant choices correspond to specific configurations of the system. Switching between these configurations and validating them manually can be complicated and can introduce errors. You can use the Variant Manager to create and save variant configurations for a model and run the model under any of the configurations. You can also validate the configurations against a set of constraints.

Analyze and Reduce Variant Configurations:

You can use the Variant Analyzer tool in the Variant Manager to compare variant configurations for a model and to determine which blocks are used in each configuration. The tool helps in model verification and validation workflows because it can identify unused regions in the model.

You can use the Variant Reducer tool in the Variant Manager to automatically generate a reduced model for a subset of variant configurations and analyze the reduced model in a detailed report. The reduction process removes inactive components for the specified variant configurations. Variant Reducer reduces associated model references, subsystem references, and libraries in the model. The tool also reduces any dependent artifacts, such as MAT or .sldd files, and packages all the reduced artifacts in a specified output folder.

Variant Manager