For Each

Control block for for-each subsystem

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Description

The For Each block serves as a control block for the For Each Subsystem block. Specifically, the For Each block enables the blocks inside the for-each subsystem to process the elements of either input signals or mask parameters independently. Each block inside this subsystem that has states maintains a separate set of states for each element or subarray that it processes. As the set of blocks in the subsystem processes the elements or subarrays, the subsystem concatenates the results to form output signals.

Use a for-each subsystem to iteratively compute outputs after changing inputs or mask parameters. To do so, configure the partitioning of input signals or mask parameters in the For Each block dialog box.

Partition Input Signals to the Subsystem

To specify which input signals to partition for each iteration in a for-each subsystem, use the Input Partition tab in the dialog box of the For Each block. When specifying a signal to be partitioned, specify the Partition Dimension, Partition Width, and Partition Offset parameters.

Partition Mask Parameters of the Subsystem

You can partition the mask parameters of a For Each Subsystem block. Partitioning is useful for systems that have identical structures in each iteration but different parameter values. In this case, changing the model to partition extra input signals for each parameter is cumbersome. Instead, add a mask parameter to a for-each subsystem. For more information, see Create a Simple Mask. To select the mask parameter for partitioning, use the Parameter Partition tab of the For Each block dialog box. For more information, see Select Partition Parameters, below.

Concatenate Output

Define the dimension along which to concatenate the results by specifying the Concatenation Dimension in the Output Concatenation tab.

The results generated by the block for each subarray are stacked along the concatenation dimension. By default, dimension 1 (y-axis) is used, meaning that the results are stacked vertically. However, if you specify a concatenation dimension of 2, the results concatenate along the horizontal direction (x-axis). Thus, if the process generates row vectors, then the concatenated result is a matrix in the first case and a row vector in the second case.

Select Partition Parameters

When selecting an input signal or subsystem mask parameter for partitioning, you need to specify how to decompose it into elements or subarrays for each iteration. Do this by setting integer values for the Partition Dimension, Partition Width, and Partition Offset parameters.

As an illustration, consider an input signal matrix A of the form:

The labels d₁ and d₂, respectively, define dimensions 1 and 2. If you retain the default setting of 1 for both the partition dimension and the partition width, and 0 for the partition offset, then Simulink^® slices perpendicular to partition dimension 1 at a width equal to the partition width, that is one element:

Matrix A decomposes into these three row vectors:

If instead you specify 2 as the partition dimension, Simulink slices perpendicular to dimension 2 to form three column vectors:

In addition to setting the Partition Dimension to 2, if you set the Partition Width to 2 and the Partition Offset to -1, Simulink uses two overlapping 3-by-2 partitions for processing.

By default, all partitions of the input signal or mask parameter are processed. To process a subset of the partitions, enter the number of partitions to process as the Number of iterations. In the matrix examples above, if Partition Offset is set to 0 (the default) and Number of iterations is set to 2, only the first 2 rows or columns of the input matrix A are processed.

Note

Only signals are considered one-dimensional in Simulink. Mask parameters are row or column vectors, according to their orientation. To partition a row vector, specify the partition dimension as 2 (along the columns). To partition a column vector, specify the partition dimension as 1 (along the rows).

Examples

Partitioning an Input Signal with the For Each Block

The following model demonstrates the partitioning of an input signal by a For Each block.

• Open Script

Specifying the Concatenation Dimension in the For Each Block

Specify a concatenation dimension in the For Each block.

• Open Script

Tiled Processing of 2-D Signals with For-Each Subsystem

Use a for-each subsystem. In this example, the operations are performed on matrices.

• Open Model

Vectorizing a Scalar Algorithm with a For-Each Subsystem

Use the for-each subsystem. In this example, the operations are performed on a vector for simplicity.

• Open Model

Modeling Objects with Identical Dynamics Using For Each Subsystem

Model multiple objects with identical dynamics using the For Each subsystem. The number of objects is parameterized by the length of the input signal.

• Open Model

Ports

Output

Partition index — Index of current partition

scalar

Index of current partition (starting at zero), returned as a scalar.

Dependencies

To enable this port, select Show partition index output port.

Data Types: int32 | double

Parameters

Input Partition Tab

Select each input signal you want to partition and specify the corresponding Partition Dimension, Partition Width, and Partition offset parameters. For more information, see Inport.

Port — List of input ports

input port name

This parameter is read-only.

List of input ports connected to the For Each Subsystem block.

Partition — Select input port signals to partition

off (default) | on

Select input port signals connected to the For Each Subsystem block to partition into subarrays or elements. For each port listed in the Port column, select the corresponding check box to partition that signal.

Programmatic Use

Block Parameter: InputPartition

Type: character vector

Values: 'off' | 'on'

Default: 'off'

Partition Dimension — Specify dimension

1 (default) | 2 | positive integer

Specify the dimension through which to slice the selected input signal array. The resulting slices are perpendicular to the dimension that you specify. The slices partition the array into subarrays or elements, as appropriate.

1

Slice input array along the columns.

2

Slice input array along the rows.

n

Slice input array along dimension n.

Dependencies

To enable this parameter, select Partition for the relevant input port.

Programmatic Use

Block Parameter: InputPartitionDimension

Type: cell array of character vectors

Values: {'1'} | {'2'} | positive integer

Default: {'1'}

Partition Width — Specify width

1 (default) | positive integer

Specify the width of each partition slice of the selected input signal.

Dependencies

To enable this parameter, select Partition for the relevant input port.

Programmatic Use

Block Parameter: InputPartitionWidth

Type: cell array of character vectors

Values: {'1'} | integer

Default: {'1'}

Partition Offset — Specify partition offset

0 (default) | integer

Specify the offset for each partition slice of the selected input signal.

0

No offset between partition slices, that is, partition slices have no gaps between them and do not overlap.

integer

Specify partition offset, using a positive integer to specify a gap between slices or a negative integer to indicate an overlap. The sum of the Partition Width and the Partition Offset must be a positive integer.

For example, a Partition Width of 3 and a Partition Offset of -2 indicates that each 3-element slice overlaps its neighboring slices by 2 elements; whereas a Partition Width of 2 and a Partition Offset of 1 indicates that there is a 1-element-wide gap between each pair of neighboring 2-element-wide slices.

Dependencies

To enable this parameter, select Partition for the relevant input port.

Programmatic Use

Block Parameter: InputPartitionOffset

Type: cell array of character vectors

Values: {'0'} | integer

Default: {'0'}

Parameter Partition Tab

Select each mask parameter you want to partition and specify the corresponding Partition Dimension and Partition Width parameters.

Parameter — List of mask parameters

parameter name

This parameter is read-only.

List of mask parameters for the For Each Subsystem block.

Dependencies

Mask parameters appear in the list only if you have added an editable parameter to the mask of the For Each Subsystem block. See Author Block Masks.

Partition — Select mask parameters to partition

off (default) | on

Select mask parameters for the For Each Subsystem block to partition into subarrays or elements. For each port listed in the Parameter column, select the corresponding check box to partition that mask parameter.

Programmatic Use

Block Parameter: SubsysMaskParameterPartition

Type: character vector

Values: 'off' | 'on'

Default: 'off'

Partition Dimension — Specify dimension

1 (default) | 2 | positive integer

Specify the dimension through which to slice the selected mask parameter array. The resulting slices are perpendicular to the dimension that you specify. The slices partition the array into subarrays or elements, as appropriate.

1

Slice mask parameter array along the columns.

2

Slice mask parameter array along the rows.

n

Slice mask parameter array along dimension n.

Dependencies

To enable this parameter, select Partition for the relevant mask parameter.

Programmatic Use

Block Parameter: SubsysMaskParameterPartitionDimension

Type: cell array of character vectors

Values: {'1'} | integer

Default: {'1'}

Partition Width — Specify partition width

1 (default) | positive integer

Specify the width of each partition slice of the selected mask parameter array.

Dependencies

To enable this parameter, select Partition for the relevant mask parameter.

Programmatic Use

Block Parameter: SubsysMaskParameterPartitionWidth

Type: cell array of character vectors

Values: {'1'} | positive integer

Default: {'1'}

Output Concatenation Tab

For each output port, specify the dimension along which to stack (concatenate) the For Each Subsystem block results. For more information, see Outport.

Port — List of output ports

output port name

This parameter is read-only.

List of output ports connected to the For Each Subsystem block.

Concatenation Dimension — Specify dimension

1 (default) | 2 | positive integer

For each output port, specify the dimension along which to stack the results of the For Each Subsystem block.

1

Stack the results in the d₁ direction, that is, vertically. If the block generates column vectors, the concatenation process results in a single column vector. If the block generates row vectors, the concatenation process results in a matrix.

2

Stack the results in the d₂ direction, that is, horizontally. If the block generates row vectors, the concatenation process results in a single row vector. If the block generates row vectors, the concatenation process results in a matrix.

n

Stack the results in the d_n direction.

Programmatic Use

Block Parameter: OutputConcatenationDimension

Type: cell array of character vectors

Values: {'1'} | integer

Default: {'1'}

Other Parameters

Show partition index output port (zero-based indexing) — Control display of output port

off (default) | on

Control display of output port for partition index.

off

Hide output port.

on

Display output port on block.

Programmatic Use

Block Parameter: ShowIterationIndex

Type: character vector

Values: 'off' | 'on'

Default: 'off'

Partition index output data type — Specify partition index data type

'int32' (default) | 'double'

Specify partition index data type for output port.

int32

Select signed 32-bit integer.

double

Select double real.

Dependencies

To enable this parameter, select Show partition index output port.

Programmatic Use

Block Parameter: IterationIndexDataType

Type: character vector

Values: 'int32' | 'double'

Default: 'int32'

Number of iterations — Specify number of partitions to process

-1 (default) | integer

To process a subset of data, specify the number of partition slices of the input signal or mask parameter array to process, else specify -1 to process all slices. The number must not be greater than the total number of slices available.

-1

Process all slices

integer

Number of slices to process

For example, a Number of iterations of 3 indicates that only the first 3 slices are to be processed.

Programmatic Use

Block Parameter: SpecifiedNumIters

Type: character vector

Values: '-1' | integer in quotes

Default: '-1'

Extended Capabilities

HDL Code Generation

Generate VHDL, Verilog and SystemVerilog code for FPGA and ASIC designs using HDL Coder™.

HDL Coder™ provides additional configuration options that affect HDL implementation and synthesized logic.

HDL Architecture

This block has one default HDL architecture.

Version History

Introduced in R2010a

R2024b: Add signal breakpoints and port value labels to iteration number outputs in iterator subsystems

You can now pause a simulation on a particular iteration of an iterator subsystem by adding signal breakpoints to signals produced by:

• Iteration number output ports of While Iterator blocks inside While Iterator Subsystem blocks

• Iterator value output ports of For Iterator blocks inside For Iterator Subsystem blocks

• Partition index output ports of For Each blocks inside For Each Subsystem blocks

In previous releases, you could add a breakpoint in these locations, but the breakpoints did not pause the simulation and appeared as invalid in the block diagram.

Port value labels at the same locations now display the iteration number. In previous releases, port value labels at these locations showed inaccessible.

For an example, see Debug Simulation of Iterator Subsystem.