Direct Lookup Table (n-D)

Index into n-dimensional table to retrieve element, vector, or 2-D matrix

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Library:
Simulink / Lookup Tables
HDL Coder / Lookup Tables

Description

The Direct Lookup Table (n-D) block indexes into an n-dimensional table to retrieve an element, vector, or 2-D matrix. The first selection index corresponds to the top (or left) input port. You can choose to provide the table data as an input to the block, or define the table data on the block dialog box. The number of input ports and the size of the output depend on the number of table dimensions and the output slice you select.

If you select a vector from a 2-D table, the output vector can be a column or a row, depending on the model configuration parameter settingMath and Data Types>Use algorithms optimized for row-major array layout．The block inputs are zero-based indices (for more information, see theInputs select this object from tableparameter.

TheDirect Lookup Tableblock supports symbolic dimensions.

Block Inputs and Outputs

The Direct Lookup Table (n-D) block uses inputs as zero-based indices into ann-dimensional table. The number of inputs varies with the shape of the output: an element, vector, or 2-D matrix.

You define a set of output values as theTable dataparameter. For the default column-major algorithm behavior, the first input specifies the zero-based index to the table dimension that is one higher than the output dimensionality. The next input specifies the zero-based index to the next table dimension, and so on.

Output Shape	Output Dimensionality	Table Dimension that Maps to the First Input
Element	0	1
Vector	1	2
Matrix	2	3

Suppose that you want to select a vector of values from a 4-D table.

The following mapping of block input port to table dimension applies.

This input port...	Is the index for this table dimension...
1	2
2	3
3	4

Changes in Block Icon Appearance

Depending on parameters you set, the block icon changes appearance. For table dimensions higher than 4, the icon matches the 4-D version but shows the exact number of dimensions at the top.

When you use theTable dataparameter, you see these icons for the default column-major behavior. Some icons are different when you select the configuration parameterMath and Data Types>Use algorithms optimized for row-major array layout．

Object that Inputs Select from the Table

Number of Table Dimensions

Element

Vector

2-D Matrix

Not applicable

When you use the table input port, you see these icons.

Object that Inputs Select from the Table

Number of Table Dimensions

Element

Vector

2-D Matrix

Not applicable

Ports

Input

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`Port_1`— Index`i1`input values
scalar | vector

For the default column-major algorithm, the first input port, specifying the zero-based index to the table dimension that is one higher than the output dimensionality (0, 1, or 2). The next input specifies the zero-based index to the next table dimension, and so on. All index inputs must be real-valued.

`Port_N`— Index`N`input values
scalar | vector

For the default column-major algorithm, the N-th input port, specifying the zero-based index to the table dimension that is N higher than the output dimensionality (0, 1, or 2). The number of inputs varies with the shape of the output. All index inputs must be real-valued.

`T`— Table data
vector | matrix | N-D array

Table data, specified as a vector, matrix, or N-D array. The table size must match the dimensions of theNumber of dimensionsparameter. The block's output data type is the same as the table data type.

Dependencies

To enable this port, select theMake table an inputcheck box.

Output

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`Port_1`— Output element, vector, or 2-D matrix
scalar | vector | 2-D matrix

Output slice, provided as a scalar, vector, or 2-D matrix. The size of the block output is determined by the setting of theInputs select this object from tableparameter. The output data type is the same as the table data type.

Parameters

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Main

Table

`Number of table dimensions`— Number of dimensions of table data
`2`(default) |`1`|`3`|`4`

Number of dimensions that theTable dataparameter must have. This value determines the number of independent variables for the table and the number of inputs to the block.

To specify...	Do this...
1, 2, 3, or 4	Select the value from the drop-down list.
一个更高的number of table dimensions	Enter a positive integer directly in the field. The maximum number of table dimensions that this block supports is 30.

To specify...

Do this...

1, 2, 3, or 4

Select the value from the drop-down list.

一个更高的number of table dimensions

Enter a positive integer directly in the field.

The maximum number of table dimensions that this block supports is 30.

Programmatic Use

Block Parameter:NumberOfTableDimensions

Type:character vector

Values:'1' | '2' | '3' | '4' | ... |'30'|

Default:'2'

`Make table an input`— Provide table data as a block input
`off`(default) |`on`

Select this check box to provide table data to the Direct Lookup Table (n-D) block as a block input. When you select this check box, a new input port,T, appears. Use this port to input the table data.

Programmatic Use

Block Parameter:TableIsInput

Type:character vector

Values:'off' | 'on'

Default:'off'

`Table data`— Table of output values
`[4 5 6; 16 19 20; 10 18 23]`(default) |`scalar, vector, matrix, or N-D array`

Specify the table of output values. The table size must match the dimensions of theNumber of table dimensionsparameter.

Tip

During block diagram editing, you can leave theTable datafield empty. But for simulation, you must match the number of dimensions inTable datato theNumber of table dimensions．For details on how to construct multidimensional MATLAB^®arrays, seeMultidimensional Arrays．

ClickEditto open the Lookup Table Editor. For more information, seeEdit Lookup Tables．

Dependencies

To enable theTable datafield, clear theMake table an inputcheck box.

Programmatic Use

Block Parameter:Table

Type:character vector

Values:scalar, vector, matrix, or N-D array

Default:'[4 5 6;16 19 20;10 18 23]'

Algorithm

`Inputs select this object from table`— Specify whether output is an element, vector, or 2-D matrix
`Element`(default) |`Vector`|`2-D Matrix`

Specify whether the output data is a single element, a vector, or a 2-D matrix. The number of input ports for indexing depends on your selection.

Selection	Number of Input Ports for Indexing
`Element`	Number of table dimensions
`Vector`	Number of table dimensions -1
`2-D Matrix`	Number of table dimensions -2

This numbering matches MATLAB indexing. For example, if you have a 4-D table of data, follow these guidelines.

To access...	Specify...	As in...
An element	Four indices	`array(1,2,3,4)`
A vector	Three indices	`array(:,2,3,4)`(default column-major algorithm)
A 2-D matrix	Two indices	`array(:,:,3,4)`(default column-major algorithm)

Tips

当Math and Data Types>Use algorithms optimized for row-major array layoutconfiguration parameter is set, the Direct Lookup Table block behavior changes from column-major to row-major. For this block, the column-major and row-major algorithms may differ semantically in output calculations, resulting in different numerical values. For example, assume thatInputs select this object from tableparameter is set toVector．The elements of the selected vector are contiguous in the table storage memory. This table shows the column-major and row-major algorithm depending on the table dimension:

Table Dimension	Column-Major Algorithm	Row-Major Algorithm
2-D table	Column vector is selected	Row vector is selected
3-D and higher table	Output vector is selected from the first dimension of the table	Output vector is selected from the last dimension of the table

Consider the row-major and column-major direct lookup algorithms with vector output from a 3-D table. The last dimension is the third dimension of a 3-D table. Due to semantic changes, column-major and row-major direct lookup may output different vector size and numerical values.

This figure shows aDirect Lookup Table (n-D)block configured with a 3-D table and a vector output. By default, the block icon shows the column-major algorithm.

To have the same block use the row-major algorithm, change theMath and Data Types>Use algorithm optimized for row-major layoutconfiguration parameter of the model and recompile. The block icon changes to reflect the change to the algorithm optimized for row-major behavior.

For more information on row-major support, seeRow-Major Array Layout: Simplify integration with external C/C++ code for Lookup Table and other blocks(Simulink Coder)．

Programmatic Use

Block Parameter:InputsSelectThisObjectFromTable

Type:character vector

Values:'Element' | 'Vector' | '2-D Matrix'

Default:'Element'

`Diagnostic for out-of-range input`— Block action when input is out of range
`Warning`(default) |`None`|`Error`

Specify whether to show a warning or error when an index is out of range with respect to the table dimension. Options include:

None— Produce no response.
Warning— Display a warning and continue the simulation.
Error— Terminate the simulation and display an error.

When you selectNoneorWarning, the block clamps out-of-range indices to fit table dimensions. For example, if the specified index is 5.3 and the maximum index for that table dimension is 4, the block clamps the index to 4.

Programmatic Use

Block Parameter:DiagnosticForOutOfRangeInput

Type:character vector

Values:'None' | 'Warning' | 'Error'

Default:'Warning'

`Sample time`— Specify sample time as a value other than`-1`
`-1`(default) | scalar | vector

Specify the sample time as a value other than -1. For more information, seeSpecify Sample Time．

Dependencies

This parameter is not visible unless it is explicitly set to a value other than-1．To learn more, seeBlocks for Which Sample Time Is Not Recommended．

Programmatic Use

Block Parameter:SampleTime

Type:character vector

Values:标量或矢量

Default:'-1'

Code generation

`移除保护啊ut-of-range input in generated code`— Remove code that checks for out-of-range input values
`off`(default) |`on`

Specify whether or not to include code that checks for out-of-range input values.

Check Box Result When to Use

Check Box	Result	When to Use
`on`	Generated code does not include conditional statements to check for out-of-range breakpoint inputs. 当input is out-of-range, it may cause undefined behavior for generated code.	For code efficiency
`off`	Generated code includes conditional statements to check for out-of-range inputs.	For safety-critical applications

on

Generated code does not include conditional statements to check for out-of-range breakpoint inputs.

当input is out-of-range, it may cause undefined behavior for generated code.

For code efficiency

off

Generated code includes conditional statements to check for out-of-range inputs.

For safety-critical applications

If your input is not out of range, you can select the移除保护啊ut-of-range index in generated codecheck box for code efficiency. By default, this check box is cleared. For safety-critical applications, do not select this check box. If you want to select the移除保护啊ut-of-range index in generated codecheck box, first check that your model inputs are in range. For example:

Clear the移除保护啊ut-of-range index in generated codecheck box.
Set theDiagnostic for out-of-range inputparameter toError．
Simulate the model in normal mode.
If there are out-of-range errors, fix them to be in range and run the simulation again.
当simulation no longer generates out-of-range input errors, select the移除保护啊ut-of-range index in generated codecheck box.

Note

When you select the移除保护啊ut-of-range index in generated codecheck box and the input is out of range, the behavior is undefined for generated code.

Depending on your application, you can run the following Model Advisor checks to verify the usage of this check box:

By Product>Embedded Coder>Identify lookup table blocks that generate expensive out-of-range checking code
By Product>Simulink Check>Modeling Standards>DO-178C/DO-331 Checks>Check usage of lookup table blocks

For more information about the Model Advisor, seeRun Model Advisor Checks．

Additionally, to determine if it is safe to select this check box, if you have a金宝app^®Design Verifier™license, consider using theDetect Block Input Range Violations(Simulink Design Verifier)check.

Programmatic Use

Block Parameter:RemoveProtectionInput

Type:character vector

Values:'off' | 'on'

Default:'off'

Table Attributes

Note

The parameters in theTable Attributespane are not available if you selectMake table an input．In this case, the block inherits all table attributes from the input port with the labelT．

`Table minimum`— Minimum value table data can have
`[]`(default) |`finite, real, double, scalar`

Specify the minimum value for table data. The default value is[](unspecified).

Programmatic Use

Block Parameter:TableMin

Type:character vector

Values:scalar

Default:'[]'

`Table maximum`— Maximum value table data can have
`[]`(default) |`finite, real, double, scalar`

Specify the maximum value for table data. The default value is[](unspecified).

Programmatic Use

Block Parameter:TableMax

Type:character vector

Values:scalar

Default:'[]'

`Table data type`— Data type of table data
`Inherit: Inherit from 'Table data'`(default) |`double`|`single`|`一半`|`int8`|`uint8`|`int16`|`uint16`|`int32`|`uint32`|`int64`|`uint64`|`boolean`|`fixdt(1,16)`|`fixdt(1,16,0)`|`fixdt(1,16,2^0,0)`|`Enum:` |

Specify the table data type. You can set it to:

A rule that inherits a data type, for example,Inherit: Inherit from 'Table data'
The name of a built-in data type, for example,single
The name of a data type class, for example, an enumerated data type class
An expression that evaluates to a data type, for example,fixdt(1,16,0)

Click theShow data type assistantbuttonto display theData Type Assistant, which helps you set the data type attributes. For more information, seeSpecify Data Types Using Data Type Assistant．

Programmatic Use

Block Parameter:TableDataTypeStr

Type:character vector

Values:

'Inherit: Inherit from 'Table data'' | 'double' | 'single' | 'half' | 'int8' | 'uint8' | 'int16' | 'uint16' | 'int32' | 'uint32' | 'int64' | 'uint64' | 'boolean' | 'fixdt(1,16)' | 'fixdt(1,16,0)' | 'fixdt(1,16,2^0,0)'|'Enum: '|''

Default:'Inherit: Inherit from 'Table data''

`Lock data type settings against changes by the fixed-point tools`— Prevent fixed-point tools from overriding data types
`off`(default) |`on`

Select this parameter to prevent the fixed-point tools from overriding the data types you specify on this block. For more information, seeLock the Output Data Type Setting(Fixed-Point Designer)．

Programmatic Use

Block Parameter:LockScale

Type:character vector

Values:'off' | 'on'

Default:'off'

Model Examples

Providing Table Data as an Input to the Direct Lookup Table Block

Provide table data as an input to the Direct Lookup Table block.

Open Model

Specifying Table Data in the Direct Lookup Table Block Dialog Box

Specify table data on the dialog box of the Direct Lookup Table (n-D) block.

Open Model

Block Characteristics

Data Types	`Boolean`\|`double`\|`enumerated`\|`fixed point^[a]`\|`一半`\|`integer`\|`single`
Direct Feedthrough	`yes`
Multidimensional Signals	`yes`
Variable-Size Signals	`no`
Zero-Crossing Detection	`no`
^[a]This block supports fixed-point data types for 'Table' data only.

Extended Capabilities

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

HDL Code Generation
Generate Verilog and VHDL 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 a single, default HDL architecture.

HDL Block Properties

ConstrainedOutputPipeline	Number of registers to place at the outputs by moving existing delays within your design. Distributed pipelining does not redistribute these registers. The default is`0`．更多细节,请参阅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 is`0`．更多细节,请参阅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 is`0`．更多细节,请参阅OutputPipeline(HDL Coder)．

Restrictions

MAX 10 Device Settings

If you use Intel^®MAX 10 device, to map the lookup table to RAM, add this Tcl command when creating the project in the Quartus tool:

set_global_assignment -name INTERNAL_FLASH_UPDATE_MODE "SINGLE IMAGE WITH ERAM"

Required Block Settings

Number of table dimensions: HDL Coder supports a maximum dimension of 5.
Inputs select this object from table: SelectElement．
Make table an input: Clear this check box.
Diagnostic for out-of-range input: SelectNone,Warning(default), orError(recommended). SelectErrorfor efficient HDL code generation. If you selectNoneorWarning, HDL Coder generates additional logic to handle out-of-range inputs.

Table Data Typing and Sizing

It is good practice to size each dimension in the table to be a power of two. If the length of a dimension (except最里面的维度)不是一个两个的力量,高清L Coder issues a warning. By following this practice, you can avoid multiplications during table indexing operations and realize a more efficient table in hardware.
All ports on the block require scalar values.

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

This block supports fixed-point data types forTable dataonly. In addition to built-in data types, the index input also supports fixed-point data type with bias equal to 0, slope equal to 1.0, fractional length equal to 0, and word length less than or equal to 128.

Direct Lookup Table (n-D)

Description

Block Inputs and Outputs

Changes in Block Icon Appearance

Ports

Input

Port_1— Indexi1input valuesscalar | vector

Port_N— IndexNinput valuesscalar | vector

T— Table datavector | matrix | N-D array

Dependencies

Output

Port_1— Output element, vector, or 2-D matrixscalar | vector | 2-D matrix

Parameters

Main

Number of table dimensions— Number of dimensions of table data2(default) |1|3|4

Programmatic Use

Make table an input— Provide table data as a block inputoff(default) |on

Programmatic Use

Table data— Table of output values[4 5 6; 16 19 20; 10 18 23](default) |scalar, vector, matrix, or N-D array

Dependencies

Programmatic Use

Inputs select this object from table— Specify whether output is an element, vector, or 2-D matrixElement(default) |Vector|2-D Matrix

Tips

Programmatic Use

Diagnostic for out-of-range input— Block action when input is out of rangeWarning(default) |None|Error

Programmatic Use

Sample time— Specify sample time as a value other than-1-1(default) | scalar | vector

Dependencies

Programmatic Use

Code generation

移除保护啊ut-of-range input in generated code— Remove code that checks for out-of-range input valuesoff(default) |on

Programmatic Use

Table Attributes

Table minimum— Minimum value table data can have[](default) |finite, real, double, scalar

Programmatic Use

Table maximum— Maximum value table data can have[](default) |finite, real, double, scalar

Programmatic Use

Table data type— Data type of table dataInherit: Inherit from 'Table data'(default) |double|single|一半|int8|uint8|int16|uint16|int32|uint32|int64|uint64|boolean|fixdt(1,16)|fixdt(1,16,0)|fixdt(1,16,2^0,0)|Enum: |

Programmatic Use

Lock data type settings against changes by the fixed-point tools— Prevent fixed-point tools from overriding data typesoff(default) |on

Programmatic Use

Model Examples

Providing Table Data as an Input to the Direct Lookup Table Block

Specifying Table Data in the Direct Lookup Table Block Dialog Box

Block Characteristics

Extended Capabilities

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

HDL Code GenerationGenerate Verilog and VHDL code for FPGA and ASIC designs using HDL Coder™.

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

See Also

Topics

Simulink Documentation

金宝app

Model-Based Design for Embedded Control Systems

`Port_1`— Index`i1`input values
scalar | vector

`Port_N`— Index`N`input values
scalar | vector

`T`— Table data
vector | matrix | N-D array

`Port_1`— Output element, vector, or 2-D matrix
scalar | vector | 2-D matrix

`Number of table dimensions`— Number of dimensions of table data
`2`(default) |`1`|`3`|`4`

`Make table an input`— Provide table data as a block input
`off`(default) |`on`

`Table data`— Table of output values
`[4 5 6; 16 19 20; 10 18 23]`(default) |`scalar, vector, matrix, or N-D array`

`Inputs select this object from table`— Specify whether output is an element, vector, or 2-D matrix
`Element`(default) |`Vector`|`2-D Matrix`

`Diagnostic for out-of-range input`— Block action when input is out of range
`Warning`(default) |`None`|`Error`

`Sample time`— Specify sample time as a value other than`-1`
`-1`(default) | scalar | vector

`移除保护啊ut-of-range input in generated code`— Remove code that checks for out-of-range input values
`off`(default) |`on`

`Table minimum`— Minimum value table data can have
`[]`(default) |`finite, real, double, scalar`

`Table maximum`— Maximum value table data can have
`[]`(default) |`finite, real, double, scalar`

`Table data type`— Data type of table data
`Inherit: Inherit from 'Table data'`(default) |`double`|`single`|`一半`|`int8`|`uint8`|`int16`|`uint16`|`int32`|`uint32`|`int64`|`uint64`|`boolean`|`fixdt(1,16)`|`fixdt(1,16,0)`|`fixdt(1,16,2^0,0)`|`Enum:` |

`Lock data type settings against changes by the fixed-point tools`— Prevent fixed-point tools from overriding data types
`off`(default) |`on`

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

HDL Code Generation
Generate Verilog and VHDL code for FPGA and ASIC designs using HDL Coder™.

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