Iterator Subsystems

Configure subsystems for repeated execution

An iterator subsystem runs one or more times at the current time step when enabled by a control block. A control block implements control logic similar to that expressed by programming language loop constructs such as while or for.

These iterator subsystems apply to general use cases:

While Iterator Subsystem block — Repeat execution of an algorithm as long as a logical condition is true.
For Iterator Subsystem block — Repeat execution of an algorithm until an iteration variable exceeds a specified iteration limit.
For Each Subsystem block — Apply an algorithm to individual elements or subarrays of input signals or mask parameters.

These iterator subsystems implement the neighborhood pattern and are optimized for large input data such as images and video:

Neighborhood Processing Subsystem block — Apply an algorithm that follows the neighborhood pattern.
Pixel Processing Subsystem block — Apply an algorithm to multichannel data such as pixels in image data.
Array Processing Subsystem block — Apply an algorithm to each element of a large array.

Each block inside a For Each subsystem that has states maintains a separate set of states for each element or subarray processed by the subsystem. By contrast, blocks inside While Iterator and For Iterator subsystems use the same states throughout successive iterations of the subsystem. The neighborhood processing iterator subsystems do not have states.

Blocks

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General Control Flow Iterator Subsystems

While Iterator Subsystem	Repeat subsystem execution during simulation time step while logical expression is true
For Iterator Subsystem	Repeat subsystem execution during simulation time step for specified number of iterations
For Each Subsystem	Apply algorithm to individual elements or subarrays of input signals or mask parameters

Neighborhood Processing Subsystems

Neighborhood Processing Subsystem	Create algorithm that follows the neighborhood pattern (Since R2022b)
Pixel Processing Subsystem	Create algorithm that converts multichannel image data to single-channel (Since R2024a)
Array Processing Subsystem	Apply algorithm to each element of a matrix (Since R2024a)

Topics

Use Control Flow Logic
How to use control flow blocks to model control logic.
Iterate Subsystem Execution with While Iterator and For Iterator Subsystems
Execute subsystem multiple times during time step in response to control block.
Repeat an Algorithm Using a For-Each Subsystem
Iterate algorithm over groups of signals, subsystems, and parameters.
Log Signals in For-Each Subsystems
Use signal logging in For Each subsystems.
Create Model That Performs Neighborhood Processing
Blur an image by using Neighborhood Processing Subsystem blocks.
Specify Region of Interest for Neighborhood Processing
Configure a Neighborhood Processing Subsystem block to iterate over a subsection of an input matrix.
Use Neighborhood Processing Subsystem Block Padding Options with Region of Interest
Configure the Neighborhood Processing Subsystem block to pad values outside the input matrix.

Featured Examples

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.

Open Live Script

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.