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While Iterator

Control block for while-iterator subsystem

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  • While Iterator block

Description

The While Iterator block, when placed in a Subsystem block, repeatedly executes the contents of the subsystem during the current time step while the value of the input condition is true or 1. Use this block to implement the block diagram equivalent of a while loop in a programming language.

The While Iterator Subsystem block is preconfigured with a While Iterator block. Placing a While Iterator block in a Subsystem block makes it an atomic subsystem.

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 the model is executed.

Parallel Channel Power Allocation

Parallel Channel Power Allocation

A potential use of the Find Nonzero Elements block. This block outputs a variable-size signal containing the indices of the nonzero values of the input.

Ports

Input

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Signal with the result from evaluating a logical condition. Because the subsystem is not externally triggered during a time step, evaluating a condition as true (1) or false (0) must reside within the subsystem.

The data type and values of the signal can be:

  • Logical (Boolean) — true (1) or false (0).

  • Numerical — true (any positive or negative number) or false (0).

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

Signal with the initial logical condition. At the beginning of each time step:

  • If IC is false (0), the subsystem does not execute during the time step.

  • If IC is true (value not equal to 0), the subsystem starts executing and continues to repeat execution as long as the cond signal is true.

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

Output Arguments

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Signal with the number of While Iterator Subsystem block executions during each time step.

Data Types: double | int8 | int16 | int32

Parameters

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Specify maximum number of iterations allowed during a time step.

-1

Any number of iterations as long as the cond signal is true (value not equal to 0). If you specify -1 and the cond signal never becomes false (0), the simulation runs in an infinite loop. In this case, the only way to stop the simulation is to terminate MATLAB®.

integer

Maximum number of iterations during a time step.

Programmatic Use

Block Parameter: MaxIters
Type: character vector
Values: '5' | '-1' | integer in quotes
Default: '5'

Select type of block.

while

The While Iterator block has two inputs, a cond (logical condition) input and an IC (initial logical condition) input. The source of the IC signal must be external to the While Iterator Subsystem block.

At the beginning of each time step:

  • If the IC input is true (value not equal to 0), the blocks in the subsystem repeat execution while the cond input is true. This process continues during a time step as long as the cond input is true and the number of iterations is less than or equal to the Maximum number of iterations.

  • If the IC input is false, the While Iterator block does not execute the contents of the subsystem.

do-while

The While Iterator block has one input, the cond (while condition) input.

At each time step, the blocks in the subsystem repeat execution while the cond input is true (value not equal to 0). This process continues as long as the cond input is true and the number of iterations is less than or equal to the Maximum number of iterations.

Programmatic Use

Block Parameter: WhileBlockType
Type: character vector
Values: 'while' | 'do-while'
Default: 'while'

Select how to handle block states between time steps.

held

Hold block states between time steps. Block state values persist across time steps.

reset

Reset block states to their initial values at the beginning of each time step and before the first iteration loop.

Programmatic Use

Block Parameter: ResetStates
Type: character vector
Values: 'held' | 'reset'
Default: 'held'

Control display of output port for signal with number of block executions. The value of the signal from this port starts at 1and is incremented by 1 for each succeeding iteration.

off

Remove output port.

on

Display output port for signal with iteration number.

Dependencies

Selecting this parameter enables the Output data type parameter.

Programmatic Use

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

Select output data type for iteration number signal. The value of this signal is the number of iterations during a time step and the total number of iterations at the end of a time step. The maximum allowable value for the signal is determined by the Output data type parameter. For example, if you set Output data type as int8, the maximum allowable value for the signal is 27-1. However, if you set Output data type as uint32 or double, the maximum allowable value for the signal is restricted to the maximum positive value for signed 32-bit integer (int32). For more information about range of values for different integer classes, see Integers.

int32

Signed 32-bit integer.

uint32

Unsigned 32-bit integer.

int16

Signed 16-bit integer.

uint16

unsigned 16-bit integer.

int8

Signed 8-bit integer.

uint8

Unsigned 8-bit integer.

double

Double-precision floating point.

Dependencies

Select the Show iteration number port check box to enable this parameter.

Programmatic Use

Block Parameter: OutputDataType
Type: character vector
Value: 'int32' | 'unt32' | 'int16' | 'uint16'|'int8' | 'uint8' | 'double'
Default: 'int32'

Version History

Introduced before R2006a

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See Also

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