Variant Start

Define start of bounded region

Since R2024a

• 

Libraries:
Simulink / Signal Routing

Description

The Variant Start block defines the start of the bounded region that allows you to limit variant condition propagation without introducing a level of hierarchy. Define the end of the bounded region by using Variant End. For every Variant Start block, there is a single corresponding Variant End block. When you specify the variant conditions on the Variant Start block, the corresponding Variant End block inherits the conditions and other parameters based on the unique Variant Start End Tag on compile.

In a given hierarchy, a region between the outport of a Variant Start block and the corresponding inport of the Variant End block is defined as a bounded region if the following conditions are met:

• You can create a subsystem that wraps all the blocks within the choice without intersecting with the other choice. Thus, there is a clear demarcation of choices.

• You can create a subsystem with only one inport(connected to the outport of the Variant Start block), and only one outport (connected to the outport of the destination). Choices do not branch out of the region.

Limitations

The Variant Start block works with time-based, and action signals. You cannot use SimEvents^®, Simscape™ Multibody™, or other non-time-based signals with these blocks.

Ports

Input

Port_1 — Input signal

scalar | vector | matrix

Input signal to be connected to the active output port.

Data Types: single | double | half | int8 | int16 | int32 | int64 | uint8 | uint16 | uint32 | uint64 | Boolean | fixed point | enumerated | bus | struct

Output

Port_1 — Output branch

scalar | vector | matrix

Output branch that forms the start of the bounded region with corresponding inport of the Variant End block.

Data Types: single | double | half | int8 | int16 | int32 | int64 | uint8 | uint16 | uint32 | uint64 | Boolean | fixed point | enumerated | bus

Port_N — Output from Nth branch

scalar | vector | matrix

Output signal from the Nth branch.

Data Types: single | double | half | int8 | int16 | int32 | int64 | uint8 | uint16 | uint32 | uint64 | Boolean | fixed point | enumerated | bus

Parameters

Variant Start End Tag — Unique identifier of bounded region

A (default) | valid MATLAB^® identifier

Unique identifier to identify the correct Variant Start and Variant End pair that form the bounded region, specified as a valid MATLAB identifier. A valid MATLAB identifier is a character vector of alphanumerics (A–Z, a–z, 0–9) and underscores, such that the first character is a letter and the length of the character vector is less than or equal to namelengthmax.

Programmatic Use

Block Parameter: VariantStartEndTag

Type: character vector

Values: 'A' | valid MATLAB identifier

Default: 'A'

Variant control mode — Variant control mode

expression (default) | label | sim codegen switching

The variant control that determines the active variant choice can be any of these types.

• expression — 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 Blocks.

• label — In label mode, Simulink chooses the active variant based on the name of the variant. The variant control is a string and does not require you to create any variable in any workspaces. See Switch Between Choices Using Labels in Variant Blocks.

• sim codegen switching — To automatically switch between the variants for simulation and code generation workflows without creating any workspace variable, use sim codegen switching mode. When you simulate a model, Simulink automatically chooses the sim branch as the active choice. Similarly, when you do a software-in-the-loop (SIL) or processor-In-Loop (PIL) simulation, generate code, or use external mode, Simulink automatically chooses the codegen branch. See Switch Between Choices for Simulation and Code Generation Workflows Without Using Control Variables in Variant Blocks.

For more information on variant control modes, see Introduction to Variant Controls. For a comparison between different types of variant control modes, see Compare Different Types of Variant Control Modes in Variant Blocks.

Dependencies

The availability of different variant activation times depends on the type of the Variant control mode that you specify. The Variant activation time parameter determines the time when Simulink sets the active choice. The parameter also determines which variability to include in the generated code. This table explains the variant activation time supported by each variant control mode.

Variant activation time
Variant control mode	update diagram	update diagram analyze all choices	code compile	startup
expression	✓	✓	✓	✓
label	✓	x	x	x
sim codegen switching	✓	✓	x	x

Programmatic Use

Block Parameter: VariantControlMode

Type: character vector

Values: expression | label | sim codegen switching |

Default: expression

Variant activation time — Time when Simulink chooses active variant choice

update diagram (default) | update diagram analyze all choices | code compile | startup | inherit from Simulink.VariantControl

This parameter determines which variability to include in the simulation and code generation workflows. For more information, see Activate Variant During Different Stages of Simulation and Code Generation Workflow.

You can set the Variant activation time parameter as:

• update diagram — When you execute the model, only the active choice is included in the simulation and the code generation workflow. Generated code contains only the active choice.

• update diagram analyze all choices — When you execute the model, both active and inactive choices are analyzed for consistency across the model. However, only the active choice is included in the simulation and the code generation workflow. Generated code contains only the active choice.

• code compile — When you execute the model, both active and inactive choices are analyzed for consistency across the model, and all choices are included in the simulation and the code generation workflow. Generated code contains both the active and inactive choices enclosed in the preprocessor conditionals #if and #elif. However, the executable built from the generated code contains only active choice.

• startup — When you execute the model, both active and inactive choices are analyzed for consistency across the model, and all choices are included in the simulation and the code generation workflow. With this option, you can improve the speed of iterative simulations using fast restart. For more information, see Run Iterative Simulations Without Recompiling Model for Variant Systems Using Fast Restart. Code generated from the model contains both the active and inactive choices that are enclosed in regular if conditions. The executable built from the generated code also contains both active and inactive choices.

• inherit from Simulink.VariantControl — When you execute the model, the block inherits the activation time from its variant control variables of type Simulink.VariantControl. If a variant block has multiple variant control variables of type Simulink.VariantControl, then all those variables must have the same activation time.

Dependencies

The availability of different variant activation times depends on the type of the variant control mode that you specify. The Variant activation time parameter determines when Simulink sets the active choice. The parameter also determines which variability to include in the generated code. This table explains the variant activation time supported by each variant control mode.

Variant activation time
Variant control mode	update diagram	update diagram analyze all choices	code compile	startup
expression	✓	✓	✓	✓
label	✓	x	x	x
sim codegen switching	✓	✓	x	x

Programmatic Use

Block Parameter: VariantActivationTime

Type: character vector

Values: update diagram | update diagram analyze all choices | code compile | startup

Default: update diagram

Port and associated conditions — Table of variant choices, variant controls, and conditions

empty table (default)

The table has a row for each variant choice connected to the output port of the Variant Start block. If there are no variant choices, the table is empty.

You can use buttons to the left of the Port and associated conditions table to modify the elements in the table.

To...	Click...
Add a new output port: Create a new output port as a variant choice and add an entry for the new choice in the table.
Delete selected port: Delete the selected variant choice from the block and its entry from the table.
Create/Edit selected variant object: Create or edit a Simulink.VariantExpression object for the selected variant choice in the global workspace and specify the variant condition using the Simulink.VariantExpression object parameter dialog box. Note For a model that uses the base workspace, this operation creates the Simulink.VariantExpression object in the base workspace, and the object is available only for the current MATLAB session. To permanently store the data, save the object in a MAT file or MATLAB script.

Port — Number of connected output port

no default

Number of the output port that is connected to one variant choice upstream of the Variant Start block. This value is read-only.

Click to add a port or to delete an existing one.

Variant control label — Name of choice in label mode

true or false (default) | string

A name for a choice, specified as a string.

Dependencies

To enable this parameter, set Variant control mode to label.

Variant control expression — Condition expression that determines the active choice

true or false (default) | boolean condition expression | a Simulink.VariantExpression object representing a boolean condition expression | (default)

Specify the condition expression to determine the active choice. When a condition expression evaluates to true, Simulink activates the corresponding variant choice. When a condition expression evaluates to false, Simulink deactivates the corresponding variant choice.

The variant controls can be:

• Boolean condition expression for rapid prototyping. For example, A == 1, A ~= B, A && B == 1, and so on.

• A Simulink.VariantExpression object that contains a condition expression for condition reuse. See Simulink.VariantExpression Objects for Variant Condition Reuse of Variant Blocks.

• Default Variant Choice if none of the choices evaluates to true.

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 Blocks and Storage Locations for Variant Control Variables (Operands) in Variant Blocks. For information on operators, see Types of Operators in Variant Blocks for Different Activation Times.

For more information, see Switch Between Choices Using Condition Expressions in Variant Blocks.

Note

In Variant Assembly Subsystem block, this parameter is a list of auto-generated boolean expressions with Variant control variable on the left-hand side and the members of the Variant enumeration choice are on the right-hand side of the expressions. Both the sides of the expressions are connected with ==. This parameter is read-only.

Programmatic Use

Structure field: Represented by the read-only variant.Name field in the Variant parameter structure

Type: character vector

Value: variant control that is associated with the variant choice

Default: 'variant'

Condition (read-only) — Condition expression in Simulink.VariantExpression object

N/A (default)

This parameter is read-only.

This parameter displays the condition expression specified as Simulink.VariantExpression object. To change or edit the condition expression, use the Simulink.VariantExpression parameter dialog box that appears when you double-click the object in the workspace.

Note

The operands that you specify in a condition expression of type Simulink.VariantExpression must be defined in the base workspace or a data dictionary. Specifying operands that are defined in the mask or model workspace is not supported.

Label mode active choice — Name of active choice in label mode

true(Subsystem) (default) | false(Subsystem1)

This list contains the labels of all the variant choices. To set an active choice, select a label from the list. The corresponding choice becomes active. Alternatively, you can follow the approaches described in Set Active Choices Using Variant Control Labels to change the active choice in label mode.

Dependencies

To enable this parameter, set the Variant control mode parameter to label.

Programmatic Use

Parameter: LabelModeActivechoice

Type: character vector

Value: if no label mode active choice is specified, the value is empty. If label mode active choice is specified, the value is the name of the label mode active choice.

Default: ''

Show variant condition on block — Annotate block ports

off (default) | on

When you select this option, Simulink annotates the variant condition expression on each port of the Variant Start block.

Programmatic Use

Block Parameter: ShowConditionOnBlock

Type: character vector

Values: 'off' | 'on'

Default: 'off'

Block Characteristics

Data Types	Boolean | bus | double | enumerated | fixed point | half | integer | single | string
Direct Feedthrough	no
Multidimensional Signals	no
Variable-Size Signals	no
Zero-Crossing Detection	no

Extended Capabilities

C/C++ Code Generation
Generate C and C++ code using Simulink® Coder™.

Fixed-Point Conversion
Design and simulate fixed-point systems using Fixed-Point Designer™.

Version History

Introduced in R2024a