If

Select subsystem execution using logic similar to if-else statement

expand all in page
  • Library:

  • Simulink / Ports & Subsystems

  • If block

Description

The If block, along with If Action Subsystem blocks containing an Action Port block, implements if-else logic to control subsystem execution. For an example using the If block, see If Action Subsystems.

Limitations

The If block has the following limitations:

  • It does not support tunable parameters. Values for an if or elseif expression cannot be tuned during a simulation in normal or accelerator mode, or when running generated code.

    To implement tunable if-else expressions, tune the expression outside the If block. For example, use the Relational Operator block to evaluate the expression outside of the If block or add the tunable parameter as an input to the If block.

  • It does not support custom storage classes. See Organize Parameter Data into a Structure by Using Struct Storage Class (Embedded Coder).

  • The If expression and Elseif expressions cannot accept certain operators, such as +, -, *, and /.

Ports

Input

expand all

Inputs u1,u2,...,un must have the same data type. The inputs cannot be of any user-defined type, such as an enumerated type.

The If block does not directly support fixed-point data types. However, you can use the Compare To Constant block to work around this limitation. See Support for Fixed-Point Data Type in If Action Subsystems.

The If block does not support a boolean data type. If you want to input a boolean signal to an If block, convert the signal to an integer type using the Data Type Conversion block.

Data Types: single | double | int8 | int16 | int32 | uint8 | uint16 | uint32

Output

expand all

Outputs from the if, else, and elseif ports are action signals to If Action Subsystem blocks.

Support for Fixed-Point Data Type

Parameters

expand all

1

Specify one input port.

integer

Specify the number of input ports. Block ports are labeled with a 'u' character followed by a number, 1,2,...,n, where n equals the number of inputs that you specify.

Programmatic Use

Block Parameter: NumInputs
Type: character vector
Values: '1' | '<integer>'
Default: '1'

The If Action Subsystem attached to the if port executes when its associated expression evaluates to true.

u1 > 0

Specify sending an action signal on the output port when the input u1 is greater than 0.

logical expression

Specify logical expression. This expression appears on the If block adjacent to the if output port.

The expression can include only the operators <, <=, ==, ~=, >, >=, &, |, ~, (), unary-minus. Operators such as +, -, *, /, and ^ are not allowed. The expression must not contain data type expressions, for example, int8(6), and must not reference workspace variables whose data type is other than double or single.

Programmatic Use

Block Parameter: IfExpression
Type: character vector
Values: 'u1 > 0' | '<logical expression>'
Default: 'u1 > 0'

The If Action Subsystem attached to an elseif port executes when its expression evaluates to true and all if and elseif expressions are false.

empty

Logical expressions not specified.

list of logical expressions

Specify a list of logical expressions delimited by commas. The expressions appear on the If block below the if port and above the else port when you select the Show else condition check box.

Expressions can include only the operators <, <=, ==, ~=, >, >=, &, |, ~, (), unary-minus. Operators such as +, -, *, /, and ^ are not allowed. The expressions must not contain data type expressions, for example, int8(6), and must not reference workspace variables whose data type is other than double or single.

Programmatic Use

Block Parameter: ElseIfExpressions
Type: character vector
Values: '' | '<list of logical expressions>'
Default: ''

When the if port and all elseif port expressions are false, the else port sends an action signal to execute the attached If Action Subsystem block.

on

Display else port.

off

Hide else port.

Programmatic Use

Block Parameter: ShowElse
Type: character vector
Values: 'on' | 'off'
Default: 'on'

Control zero-crossing detection.

on

Detect zero crossings.

off

Do not detect zero crossings.

Programmatic Use

Block Parameter: ZeroCross
Type: character vector
Values: 'on' | 'off'
Default: 'on'

Model Examples

Simulink Subsystem Semantics

Simulink Subsystem Semantics

This set of examples shows different types of Simulink® Subsystems and what semantics are used when simulating these Subsystems. Each example provides a description of the model and the subtleties governing how it will be executed.

Open Model
If-Then-Else Blocks

If-Then-Else Blocks

What happens when a sine wave is fed into an If block. After running the simulation, the scope shows three plots. This example is designed to compare the If block with enabled subsystems.

Open Model
Modeling Clutch Lock-Up Using If Blocks

Modeling Clutch Lock-Up Using If Blocks

Use If/Else subsystems to build a clutch model. An 'If' subsystem models the clutch dynamics in the locked position while an 'Else' subsystem models the unlocked position. One or the other is enabled using the 'If' block. The dot-dashed lines from the 'If' block denote control signals, which are used to enable If/Else (or other conditional) subsystems. Checking any of the boxes on the GUI produces a plot of any of the selected variables (versus time).

Open Model

Block Characteristics

Data Types

Boolean | double | integer | single

Direct Feedthrough

yes

Multidimensional Signals

no

Variable-Size Signals

no

Zero-Crossing Detection

yes

Extended Capabilities

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

See Also

Blocks

Topics

Introduced before R2006a

Simulink Documentation

Support