Selector

R2026b

Select input elements from vector, matrix, or multidimensional signal

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Selector block

To add a block to a model, double-click the canvas and start typing the block name. Then, select the block from the list.

Libraries:
Simulink / Signal Routing
HDL Coder / Signal Routing

Description

The Selector block extracts selected elements of an input vector, matrix, or multidimensional signal based on specified indices. The extracted signals can be grouped differently than the input signals.

Based on the value you enter for the Number of input dimensions parameter, a table of indexing settings is displayed. Each row of the table corresponds to one of the input dimensions in Number of input dimensions. For each dimension, you define the elements of the signal to work with. Specify a vector signal as a 1-D signal and a matrix signal as a 2-D signal. When you configure the Selector block for multidimensional signal operations, the block icon changes.

For example, assume a 6-D signal with a one-based index mode. The table of the Selector block dialog box changes to include one row for each dimension. If you define dimensions as shown in the next table, the output is Y = U(1:end,2:6,[1 3 5],Idx4:Idx4+7,Idx5,Idx6(1):Idx6(2)), where Idx4, Idx5, and Idx6 are the index ports for dimensions 4, 5, and 6. For more information, see Select Elements from Multidimensional Array Using Selector Block.

Row	Index Option	Index	Output Size
1	Select all
2	Starting index (dialog)	2	5
3	Index vector (dialog)	[1 3 5]
4	Starting index (port)		8
5	Index vector (port)
6	Starting and ending indices (port)

You can use an array of buses as an input signal to a Selector block. For details about defining and using an array of buses, see Group Nonvirtual Buses in Arrays of Buses.

Note

Selector block does not change the dimensionality (number of dimensions) of the input signals. If you need to change the dimensionality of the signal to the dimensions you specify, use Reshape block.

Examples

Index Options with the Selector Block

This example shows two Selector blocks with the same kind of input signals, but two different Index Option settings.

Both Selector blocks select 7 values from the input signal that feeds the input port. The Selector1 block outputs a fixed-size signal, whereas the Selector2 block outputs a variable-size signal whose compiled signal dimension is 10 instead of 7.

The Selector1 block sets Index Option to Index vector (port), which uses the input signal from Constant1 as the index vector. The dimension of the input signal is 7, so the Display block shows the 7 values of the Constant1 block. The Selector2 block sets the Input port size parameter to 10, which is the size of the largest input signal to the Selector2 block.

The Selector2 block also sets the Index Option to Starting and ending indices (port). The output is then set to the size of Input port size parameter (10), even though the size of the input signal is 7.

Select Elements from Multidimensional Array Using Selector Block

This example shows how to select elements from a multidimensional array using a Selector block. In this example, you use different indexing options of the block to select and extract the elements of a 6-D array.

Open the model.

mdl = "extractmultidimarray.slx";
open_system(mdl)

Configure the Block

The input array U is a 6-D array with dimensions 6-by-6-by-6-by-9-by-7-by-5 with a one-based index mode. The model loads the input array from the inputSignal file by using model PreLoadFcn callback. You can select elements from each dimension of the array using the following selection semantics and different index options. In this example, one-based index mode is used for the input array. Consequently, the row numbers (first column of the table) directly indicate the dimensions of the input array. For example, row 1 indicates dimension 1 of the input array, and so on.

• To extract all of the elements of dimension 1, use Select All.

• To extract the third and fourth elements of dimension 2, use Starting Index (dialog). Set Index column to 3 and Output Size column to 2.

• To extract the first, third, and fifth element of dimension 3, use Index vector (dialog). Set Index column to [1 3 5].

• To extract the first eight elements of dimension 4, use Starting Index (port). The Constant block Const1 connected to port $${\text{Idx4}}_1$$ provides the starting index value 1. Set the Output Size column to 8.

• To extract the second, third, and fourth elements of dimension 5, use Index vector (port). The Constant block Const2 connected to port $${\text{Idx5}}_1$$ provides the index value [2:4].

• To extract a range of elements from dimension 6, use Starting and ending indices (port). The selection ranges from the third to the fifth element. The Constant block Const3 connected to port $${\text{Idx6}}_1$$ provides the range [3 5].

Log signal

Run the simulation and use the To Workspace block to log the signal to the variable Y.

Y = sim(mdl);

Extended Examples

Bounded Variable-Size Signal Basic Operations

Generate bounded variable-size signals and illustrates some of the operations using those signals. In this example, you generate variable-size signals using the Selector block and the Switch block. The signals are used in math operations, bus creation, bus selection, matrix concatenation and to implement a discrete filter equation.

• Open Model

Multimode Variable-Size Signal

Use different operation modes to correspond to different signal sizes.

• Open Model

Model Arrays of Buses

Use arrays of buses to represent structured data compactly.

• Open Live Script

Limitations

• The Index parameter is not tunable during simulation. If the Index Option for a dimension is set to Index vector (dialog) or Starting index (dialog) and you specify a symbolic value, including a Simulink.Parameter object, for the corresponding Index in the block dialog box, then the instantaneous value at the start of simulation will be used throughout the simulation, and the parameter will appear as an inlined value in the generated code. See Tune and Experiment with Block Parameter Values. You can adjust the selection index dynamically by using index ports.

Ports

Input

Port_1 — Input signal

scalar | vector | matrix | multidimensional

Input signal and source of elements to output signal.

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

IndxN — Nth index signal

scalar | vector | matrix

External port specifying an index for the selection of the corresponding output element.

You can specify integer of custom width (for example, a 15-bit integer or 23-bit integer) as an index signal value. When you configure the width of the integer, you must specify the Mode as Fixed point, with Word length less than or equal to 65,535, Slope equal to 1, and Bias equal to 0. For more information on specifying a fixed-point data type, see Specify Data Types Using Data Type Assistant.

Dependencies

To enable an external index port, in the corresponding row of the Index Option table, set Index Option to Index vector (port), Starting index (port), or Starting and ending indices (port).

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

Output

Port_1 — Output signal

scalar | vector | matrix | multidimensional

Output signal generated from selected or reordered elements of input signal.

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

Parameters

Number of input dimensions — Number of dimensions of input signal

1 (default) | integer

Specifies the number of dimensions of the input signal.

Programmatic Use

Block Parameter: NumberOfDimensions

Type: character vector

Values: integer

Default: '1'

Index mode — Index mode

One-based (default) | Zero-based

Specifies the indexing mode. If One-based is selected, an index of 1 specifies the first element of the input vector. If Zero-based is selected, an index of 0 specifies the first element of the input vector.

Programmatic Use

Block Parameter: IndexMode

Type: character vector

Values: 'One-based' | 'Zero-based'

Default: 'One-based'

Index Option — Index method for elements

Index vector (dialog) (default) | Select all | Index vector (port) | Starting index (dialog) | Starting index (port) | Starting and ending indices (port)

Defines, by dimension, how the elements of the signal are to be indexed. From the list, select:

• Select all

  No further configuration is required. All elements are selected.

• Index vector (dialog)

  Enables the Index column. Enter the vector of indices of the elements.

• Index vector (port)

  No further configuration is required.

• Starting index (dialog)

  Enables the Index and Output Size columns. Enter the starting index of the range of elements to select in the Index column and the number of elements to select in the Output Size column.

• Starting index (port)

  Enables the Output Size column. Enter the number of elements to be selected in the Output Size column.

• Starting and ending indices (port)

  No further configuration is required.

  Using this option results in a variable-size output signal. When you update, the output dimension is set to be the same as the input signal dimension. During execution, the output dimension is updated based on the signal feeding the index.

  When logging output signal data, signals not selected are padded with NaN values.

The Index and Output Size columns appear as needed.

Programmatic Use

Block Parameter: IndexOptionArray

Type: cell array of character vectors

Values: {'Select all'} | {'Index vector (dialog)'} | {'Index vector (port)'} | {'Starting index (dialog)'} | {'Starting index (port)'} | {'Starting and ending indices (port)'}

Default: {'Index vector (dialog)'}

For a character vector instead of a cell array of character vectors, use IndexOptions.

Index — Index of elements

[1 3] (default) | integer

When the Index Option is Index vector (dialog), enter the index of each element you are interested in.

When the Index Option is Starting index (dialog), enter the starting index of the range of elements to be selected.

Programmatic Use

Block Parameter: IndexParamArray

Type: cell array of character vectors

Values: integers

Default: {'[1 3]'}

For a character vector instead of a cell array of character vectors, use Indices.

Output Size — Width of block output signal

1 (default) | integer

Specifies the width of the block output signal.

Programmatic Use

Block Parameter: OutputSizeArray

Type: cell array of character vectors

Values: integers

Default: {'1'}

For a character vector instead of a cell array of character vectors, use OutputSizes.

Input port size — Width of input signal

3 (default) | integer

Specify the width of the block input signal for 1-D signals. Enter -1 to inherit from the driving block.

Programmatic Use

Block Parameter: InputPortWidth

Type: character vector

Values: integer

Default: '3'

Sample time (-1 for inherited) — Interval between samples

-1 (default) | scalar | vector

Specify the time interval between samples. To inherit the sample time, set this parameter to -1. For more information, see Specify Sample Time.

Dependencies

This parameter is visible only if you set it to a value other than -1. To learn more, see Blocks for Which Sample Time Is Not Recommended.

Programmatic Use

To set the block parameter value programmatically, use the set_param function.

Parameter:	SampleTime
Values:	"-1" (default) | scalar or vector in quotes

Check for out-of-range index in accelerated simulation — Option to check for out-of-range index values in accelerator and rapid accelerator simulation modes

off (default) | on

Select this check box to have Simulink^® check during simulation in accelerator or rapid accelerator mode whether any index values are outside the range of valid indices for the relevant dimension of the input signal. If an index is out of range, Simulink stops the simulation and displays an error message.

Note

If you do not select this check box, out-of-range index values could lead to undefined behavior during accelerator or rapid accelerator mode simulation.

Simulink performs this check during normal mode simulation regardless of whether you select this check box.

Dependencies

This parameter is hidden by default. The Selector block checks for out-of-range index values in accelerator and rapid accelerator simulation modes by default. This parameter is only enabled and visible when you programmatically set the RuntimeRangeChecks property to 'off'.

Programmatic Use

Parameter: RuntimeRangeChecks

Type: character vector

Values: 'Off' | 'On'

Default: 'Off'

Block Characteristics

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

Extended Capabilities

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

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.

HDL Block Properties

General
ConstrainedOutputPipeline	Number of registers to place at the outputs by moving existing delays in the design. Distributed pipelining does not redistribute these registers. The default value is 0. For more details, see ConstrainedOutputPipeline (HDL Coder).
InputPipeline	Number of input pipeline stages to insert in the generated code. Distributed pipelining and constrained output pipelining can move these registers. The default value is 0. For more details, see InputPipeline (HDL Coder).
OutputPipeline	Number of output pipeline stages to insert in the generated code. Distributed pipelining and constrained output pipelining can move these registers. The default value is 0. For more details, see OutputPipeline (HDL Coder).
SynthesisAttributes	Specifies the synthesis attributes for the blocks and block output signals in the model. The generated HDL code contains these attributes. For more information, see SynthesisAttributes (HDL Coder).

Native Floating Point
LatencyStrategy	Specify whether to map the blocks in your design to inherit, Max, Min, or Zero for the floating-point operator. The default is inherit. See also LatencyStrategy (HDL Coder).

Data Type Support

The block supports these data types for HDL code generation:

Input Port	Dimension	Fixed-Point	Floating-Point	Built-in Integers	Bus	Boolean	Enumerated	Complex Signal
Port1	Scalar Vector Matrix (up to 2-D)	Yes	Half Single Double	No	Yes	Yes	Yes	Yes

Optimizations

The block participates in these HDL optimizations to optimize the speed, and area.

Area Optimization

Optimization	Description
Resource Sharing (HDL Coder)	Resource sharing is an area optimization in which HDL Coder identifies multiple functionally equivalent resources and replaces them with a single resource.
Streaming (HDL Coder)	Streaming is an area optimization in which HDL Coder transforms a vector data path to a scalar data path (or to several smaller-sized vector data paths).

Speed Optimization

Optimization	Description
Specify Distributed Pipelining Settings (HDL Coder)	Distributed pipelining, or register retiming, is a speed optimization that moves existing delays in a design to reduce the critical path while preserving functional behavior.
Clock-Rate Pipelining (HDL Coder)	Clock-rate pipelining is an optimization framework in HDL Coder that allows other speed and area optimizations to introduce latency at the clock rate.
Specify Adaptive Pipelining Settings (HDL Coder)	Adaptive pipelining optimization creates patterns or combination of blocks with registers that can improve the achievable clock frequency and reduce the area usage on the FPGA boards by inserting pipeline registers to the blocks in your design.

PLC Code Generation
Generate Structured Text code using Simulink® PLC Coder™.

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

Version History

Introduced before R2006a

R2026b: Selector and Assignment blocks out-of-range check behavior change

Starting in R2026b, the Selector and Assignment blocks check for out-of-range index values in accelerator and rapid accelerator simulation modes by default. The dialog box Check for out-of-range index in accelerated simulation parameter for the Selector and Assignment blocks is now hidden and can only be programmatically enabled by using the RuntimeRangeChecks property.

If you load an existing model with these checks turned off, a warning appears stating that the .setting is not recommended. The model continues to run.

R2023a: Index signal supports integer of custom width

Starting in R2023a, you can customize the width of the integer that you use to specify the index signal value for the Selector block.

R2023a: Variable size signal support for Index vector (dialog) and Starting index (dialog) as Index Option

Starting in R2023a, a Selector block that is configured to accept a 1-D variable-size input signal, supports Index vector (dialog) and Starting index (dialog) as the Index Option.

This enhancement allows you to choose from all the available Index Option settings when you configure the Selector block to accept a1-D variable-size input signal.