Prelookup
Compute index and fraction for Interpolation Using Prelookup block
Libraries:
Simulink /
Lookup Tables
HDL Coder /
Lookup Tables
Description
The Prelookup block calculates the index and interval fraction that specify how its
input value u
relates to the breakpoint data set. The Prelookup block
works best with the Interpolation Using Prelookup block. Feed
the resulting index and fraction values into an Interpolation Using Prelookup block to
interpolate an n-dimensional table. These two blocks have
distributed algorithms. When combined together, they perform the same operation as the
integrated algorithm in the n-D Lookup Table block. However, the
Prelookup and Interpolation Using Prelookup blocks offer
greater flexibility and more efficient simulation and code generation than the
n-D Lookup Table block. For more information, see Efficiency of Performance.
Supported Block Operations
To use the Prelookup block, you must specify a set of breakpoint values. You
choose whether to specify the breakpoint values directly on the dialog box or by
feeding the values to a bp
input port by setting the
Source parameter to Dialog
or
Input port
. Typically, this breakpoint data set
corresponds to one dimension of the table data in an Interpolation Using Prelookup
block. The Prelookup block generates a pair of outputs for each input value
u
by calculating:
The index of the breakpoint set element that is less than or equal to
u
and forms an interval containingu
The interval fraction in the range 0 ≤ f < 1, representing the normalized position of
u
on the breakpoint interval between the index and the next index value for in-range input
For example, if the breakpoint data set is [0 5 10 20 50 100]
and the input value u
is 55, the index is 4 and the fractional
value is 0.1. Labels for the index and interval fraction appear as
k and f on the Prelookup block icon.
The index value is zero based.
The interval fraction can be negative or greater than 1
for
out-of-range input. See the Extrapolation method block
parameter for more information.
Examples
Prelookup with External Breakpoint Specification
This example shows how to feed a breakpoint data set from a Constant block into the bp
input port of the Prelookup block.
The Prelookup block inherits these breakpoint attributes from the bp
input port:
Minimum:
Inf
Maximum:
Inf
Data type:
single
Similarly, a Constant block feeds the table data values to the T
input port of the Interpolation Using Prelookup block, which inherits these attributes:
Minimum:
Inf
Maximum:
Inf
Data type:
single
Simulink® uses double-precision, floating-point data to perform the computations in this model. However, the model stores the breakpoint and table data as single-precision, floating-point data. Using a lower-precision data type to store breakpoint and table data reduces the memory requirement.
Prelookup with Evenly Spaced Breakpoints
This example shows how to specify evenly spaced breakpoint data in the Prelookup block.
In the Breakpoints data section, the Specification parameter is set to Even spacing
. The parameters First point, Spacing, and Number of points are set to 25
, 12
, and 4
respectively. Specifying these parameters creates four evenly spaced breakpoints: [25, 37, 49, 61]
.
An alternative way to specify evenly spaced breakpoints is to set Specification to Explicit values
and set Value to [25:12:61]
.
Simulink® uses double-precision, floating-point data to perform the computations in this model. However, the model stores the breakpoints and table data as double.
Configure the Prelookup Block to Output Index and Fraction as a Bus
This example shows how to output a bus containing the index (k
) and fraction (f
) from the Prelookup block. The bus object can then be used as an input to the Interpolation Using Prelookup block. The example also shows how to get the same results without using a bus object.
Open and simulate the model.
At the top of the model, open the dialog box for the Prelookup block. In the Main tab, note that Output selection is set to Index and fraction as bus
. In the Data Types tab, note that Output is set to Bus: myBus
. In the Simulink® Editor, select Modeling>Model Settings>Model Properties and open the Callbacks tab. In the model's PreLoadFcn
, the code defines the bus object myBus
, which specifies the index as the first bus element and the fraction as the second element.
Open the dialog box for the Interpolation Using Prelookup block. In the Main tab, note that Require index and fraction as bus check box is selected. That option configures the block to use the bus output from the Prelookup block.
Extended Examples
Using the Prelookup and Interpolation Blocks
Use the Prelookup and Interpolation Using Prelookup blocks.
Saving Memory in Prelookup and Interpolation Blocks by Using Smaller Data
Save memory in Prelookup and Interpolation blocks. The Prelookup and Interpolation Using Prelookup blocks allow you to explicitly set data type storing breakpoints and table data. Note that the Prelookup block allows the breakpoint data to differ from the input data type, and the Interpolation Using Prelookup block allows the table data to differ from the output data type.
Ports
Input
Port_1 — Input signal, u
scalar | vector | matrix
The Prelookup block accepts real-valued signals of any numeric data type that Simulink® supports, except Boolean. The Prelookup block supports fixed-point data types for signals and breakpoint data.
Data Types: half
| single
| double
| int8
| int16
| int32
| int64
| uint8
| uint16
| uint32
| uint64
| fixed point
| enumerated
| bus
bp — Breakpoint data
1-D vector of real-valued signals
The Prelookup block accepts real-valued signals as breakpoint data of any numeric data type that Simulink supports, except Boolean.
Data Types: half
| single
| double
| int8
| int16
| int32
| int64
| uint8
| uint16
| uint32
| uint64
| fixed point
| enumerated
Output
k — Index of the interval containing the input,
u
scalar | vector | matrix
The zero-based index, k, is a real-valued integer
that specifies the interval containing the input,
u
.
Dependencies
To enable this port, set the Output selection
to Index and fraction
or
Index only
.
Data Types: int8
| int16
| int32
| int64
| uint8
| uint16
| uint32
| uint64
| fixed point
f — Fraction representing the normalized position of the input, u
, within the interval,
k
scalar | vector | matrix
Fraction, f, represents the normalized position of
the input, u
, within the interval
k.
Dependencies
To enable this port, set the Output selection
to Index and fraction
.
Data Types: single
| double
| fixed point
Port_2 — Bus containing index, k, and fraction, f
bus
Outputting the index, k, and fraction f, as a bus object can help simplify the model.
Dependencies
To enable this port, set the Output selection
to Index and fraction as bus
.
Data Types: bus
Parameters
Main
Breakpoints dataSpecification — Choose how to enter breakpoint data
Explicit values
(default) | Even spacing
| Breakpoint object
If you set this parameter to:
Explicit values
, the Source and Value parameters are visible on the dialog box.Even spacing
, the First point, Spacing, and Number of points parameters are visible on the dialog box.Breakpoint object
, the Name parameter is visible on the dialog box.
Programmatic Use
Block Parameter:
BreakpointsSpecification |
Type: character vector |
Values:
'Explicit values' | 'Even spacing' | 'Breakpoint
object' |
Default:
'Explicit values' |
To set this parameter from 'Explicit values'
or
'Even spacing'
to 'Breakpoint
object'
, use the same set_param
call to set the BreakpointObject
parameter. For
example:
set_param('myModel/myPrelookupBlock',... 'BreakpointsSpecification','Breakpoint object',... 'BreakpointObject','myBPObject')
Source — Specify source of breakpoint data
Dialog
(default) | Input port
If you set Source to:
Dialog
, specify breakpoint data under Value.Input port
, verify that an upstream signal supplies breakpoint data to thebp
input port. Each breakpoint data set must be a strictly monotonically increasing vector that contains two or more elements. For this option, your block inherits breakpoint attributes from thebp
input port.
Dependencies
To enable this parameter, set Specification
to Explicit values
.
Programmatic Use
Block Parameter:
BreakpointsDataSource |
Type: character vector |
Values:
'Dialog' | 'Input port' |
Default:
'Dialog' |
Value — Breakpoint data values
[10:10:110]
(default) | vector of strictly monotonically increasing values containing two or
more elements
Explicitly specify the breakpoint data. Each breakpoint data set must be a strictly monotonically increasing vector that contains two or more elements. For this option, you specify additional breakpoint attributes on the Data Types pane.
To open the Lookup Table Editor, click Edit (see Edit Lookup Tables).
Note
When you set Specification to
Explicit values
and
Source to Input
port
, verify that an upstream signal supplies
breakpoint data to the bp
input port. Each
breakpoint data set must be a strictly monotonically increasing
vector that contains two or more elements. For this option, your
block inherits breakpoint attributes (including data type) from the
bp
input port.
Dependencies
To enable this parameter, set Specification
to Explicit values
and
Source to
Dialog
.
Programmatic Use
Block Parameter:
BreakpointsData |
Type: character vector |
Values: vector of strictly monotonically increasing values containing two or more elements |
Default:
'[10:10:110]' |
First point — First point in evenly spaced breakpoint data
10
(default) | real-valued scalar
Dependencies
To enable this parameter, set Specification
to Even spacing
.
Programmatic Use
Block Parameter:
BreakpointsFirstPoint |
Type: character vector |
Values: real-valued scalar |
Default:
'10' |
Spacing — Spacing between evenly spaced breakpoints
10
(default) | real-valued, positive scalar
Dependencies
To enable this parameter, set Specification
to Even spacing
.
Programmatic Use
Block Parameter:
BreakpointsSpacing |
Type: character vector |
Values: real-valued, positive scalar |
Default:
'10' |
Number of points — Number of evenly spaced points
11
(default) | real-valued, positive scalar
Dependencies
To enable this parameter, set Specification
to Even spacing
.
Programmatic Use
Block Parameter:
BreakpointsNumPoints |
Type: character vector |
Values: real-valued, positive scalar |
Default:
'11' |
Name — Name of a Simulink.Breakpoint
object
no default | Simulink.Breakpoint
object
Specify the name of a Simulink.Breakpoint
object. A
breakpoint object references Simulink breakpoint objects. If a Simulink.Breakpoint
object does not exist, click the
action button and select
Create. The corresponding parameters of the
new breakpoint object are automatically populated with the block
information.
Dependencies
To enable this parameter, set Specification
to Breakpoint object
.
Programmatic Use
Block Parameter:
BreakpointObject |
Type: character vector |
Values:
Simulink.Breakpoint object |
Default:
'' |
Output selection — Specify the signals the block outputs
Index and fraction
(default) | Index and fraction as bus
| Index only
If you want the block to output the index and interval fraction, you can specify whether the block outputs individual signals or a bus signal that includes both the index and fraction signals.
Index only
outputs just the index, without the fraction. Typical applications for this option include:Feeding a Direct Lookup Table (n-D) block, with no interpolation on the interval
Feeding selection ports of a subtable selection for an Interpolation Using Prelookup block
Performing nonlinear quantizations
Index and fraction
outputs the index and fraction as individual signals.Index and fraction as bus
outputs a bus signal that includes the index and fraction signals. Using a bus for these signals:Simplifies the model by tying these two related signals together
Creates a test point
DpResult
structure for the AUTOSAR 4.0 libraryFor the AUTOSAR 4.0 library, avoids the creation of extra copies during code generation when the Prelookup and Interpolation Using Prelookup blocks are in separate models
Note
Selecting
Index and fraction as bus
displays the Output parameter in the Data Types pane and sets the Output parameter toInherit: auto
. Change this default value to specify a user-defined bus object. For details about defining the bus object, see the Output parameter description.
Programmatic Use
Block Parameter:
OutputSelection |
Type: character vector |
Values:
'Index and fraction' | 'Index and fraction as bus' |
'Index only' |
Default:
'Index and fraction' |
Index search method — Method for searching breakpoint data
Binary search
(default) | Linear search
| Evenly spaced points
Each search method has speed advantages in different situations:
For evenly spaced breakpoint sets (for example, 10, 20, 30, and so on), you achieve optimal speed by selecting
Evenly spaced points
to calculate table indices. This algorithm uses only the first two breakpoints of a set to determine the offset and spacing of the remaining points.For unevenly spaced breakpoint sets, follow these guidelines:
If input values for
u
do not vary significantly between time steps, selectingLinear search
with Begin index search using previous index result produces the best performance.If input values for
u
jump more than one or two table intervals per time step, selectingBinary search
produces the best performance.
A suboptimal choice of index search method can lead to slow performance of models that rely heavily on lookup tables.
Note
The generated code stores only the first breakpoint, the spacing, and the number of breakpoints when:
The breakpoint data is not tunable.
The index search method is
Evenly spaced points
.
Programmatic Use
Block Parameter:
IndexSearchMethod |
Type: character vector |
Values:
'Evenly spaced points' | 'Linear
search' | 'Binary
search' |
Default:
'Binary search' |
Begin index search using previous index result — Start search using the index found at the previous time step
off
(default) | on
For input values of u
that change slowly with
respect to the interval size, enabling this option can improve
performance. Otherwise, the linear search and binary search methods can
take longer, especially for large breakpoint sets.
Programmatic Use
Block Parameter:
BeginIndexSearchUsingPreviousIndexResult |
Type: character vector |
Values:
'off' | 'on' |
Default:
'off' |
Extrapolation method — Method for handling out-of-range input values
Clip
(default) | Linear
Options include:
Clip
Block Input Block Outputs Less than the first breakpoint
Index of the first breakpoint (for example,
0
)Interval fraction of
0
Greater than the last breakpoint
Index of the next-to-last breakpoint
Interval fraction of
1
Suppose the range is
[1 2 3]
and you select this option. Ifu
is0.5
, the index is0
and the interval fraction is0
. Ifu
is3.5
, the index is1
and the interval fraction is1
.Linear
Block Input Block Outputs Less than the first breakpoint
Index of the first breakpoint (for example,
0
)Interval fraction that represents the linear distance from
u
to the first breakpoint
Greater than the last breakpoint
Index of the next-to-last breakpoint
Interval fraction that represents the linear distance from the next-to-last breakpoint to
u
Suppose the range is
[1 2 3]
and you select this option. Ifu
is0.5
, the index is0
and the interval fraction is-0.5
. Ifu
is3.5
, the index is1
and the interval fraction is1.5
.
Note
The Prelookup block supports linear extrapolation only when all of the following conditions are true:
The input
u
, breakpoint data, and fraction output use floating-point data types.The index uses a built-in integer data type.
To use Prelookup and Interpolation Using Prelookup blocks to replicate n-D Lookup Table block behavior, the Extrapolation method for both Prelookup and Interpolation Using Prelookup blocks must be the same as if you use only the n-D Lookup Table block. For example, to get the same behavior as the n-D Lookup Table block with Extrapolation method set to Linear
, set Extrapolation method to Linear
for both Prelookup and Interpolation Using Prelookup blocks.
Programmatic Use
Block Parameter:
ExtrapMethod |
Type: character vector |
Values:
'Clip' | 'Linear' |
Default:
'Clip' |
Use last breakpoint for input at or above upper limit — Method of handling inputs at or above upper limit
off
(default) | on
Specify how to index input values of u
that are
greater than or equal to the last breakpoint. The index value is zero
based. When input equals the last breakpoint, block outputs differ as
follows.
Check Box | Block Outputs |
---|---|
Selected ( |
|
Cleared ( |
|
Tip
When you select Use last breakpoint for input at or above upper limit for a Prelookup block, you must also select Valid index input may reach last index for the Interpolation Using Prelookup block to which it connects. This action allows the blocks to use the same indexing convention when accessing the last elements of their breakpoint and table data sets.
Dependencies
This parameter is visible only when Extrapolation
method is Clip
.
Programmatic Use
Block Parameter:
UseLastBreakpoint |
Type: character vector |
Values:
'off' | 'on' |
Default:
'off' |
Diagnostic for out-of-range input — Block action when input is out of range
None
(default) | Warning
| Error
Options include:
None
— Produce no response.Warning
— Display a warning and continue the simulation.Error
— Terminate the simulation and display an error.
Programmatic Use
Block Parameter:
DiagnosticForOutOfRangeInput |
Type: character vector |
Values:
'None' | 'Warning' | 'Error' |
Default:
'None' |
Remove protection against out-of-range input in generated code — Remove code that checks for out-of-range breakpoint inputs
off
(default) | on
Check Box | Result | When to Use |
---|---|---|
| Generated code does not include conditional statements to check for out-of-range breakpoint inputs. When the input is out-of-range, it may cause undefined behavior for generated code. | For code efficiency |
| Generated code includes conditional statements to check for out-of-range breakpoint inputs. | For safety-critical applications |
If your input is not out-of-range, you can select Remove protection against out-of-range index in generated code for code efficiency. By default, this parameter is cleared. For safety-critical applications, do not select this parameter. If you want to select Remove protection against out-of-range index in generated code, first check that your model inputs are in range. For example:
Clear Remove protection against out-of-range index in generated code.
Set Diagnostic for out-of-range input to
Error
.Simulate the model in normal mode.
If there are out-of-range errors, fix them to be in range and run the simulation again.
When the simulation no longer generates out-of-range input errors, select Remove protection against out-of-range index in generated code.
Note
When you select Remove protection against out-of-range index in generated code 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 parameter:
Additionally, to determine if it is safe to select this parameter, if you have a Simulink Design Verifier™ license, consider using the Detect Block Input Range Violations (Simulink Design Verifier) check.
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, see Run Model Advisor Checks.
Programmatic Use
Block Parameter:
RemoveProtectionInput |
Type: character vector |
Values:
'off' | 'on' |
Default:
'off' |
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 |
Data Types
Breakpoint — Breakpoint data type
Inherit: Same as input
(default) | Inherit: Inherit from 'Breakpoint data'
| double
| single
| int8
| uint8
| int16
| uint16
| int32
| uint32
| int64
| uint64
| fixdt(1,16)
| fixdt(1,16,0)
| fixdt(1,16,2^0,0)
| Enum: <class name>
| <data type expression>
Specify the breakpoint data type. You can set it to:
A rule that inherits a data type, for example,
Inherit: Same as input
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)
The Data Type Assistant helps you set data attributes. To use the Data Type Assistant, click . For more information, see Specify Data Types Using Data Type Assistant.
Tip
Specify a breakpoint data type different from the data type of input
u
for these cases:Lower memory requirement for storing breakpoint data that uses a smaller type than the input signal
u
Sharing of prescaled breakpoint data between two Prelookup blocks with different data types for input
u
Sharing of custom storage breakpoint data in the generated code for blocks with different data types for input
u
Specify the same slope and bias for a breakpoint data type and its corresponding input data type if either of them has a fixed-point data type.
Enumerated data:
Breakpoints support unordered enumerated data. As a result, linear searches are also unordered, which offers flexibility but can impact performance. The search begins from the first element in the breakpoint.
If the Begin index search using previous index result parameter is selected, you must use ordered monotonically increasing data. This ordering improves performance.
For enumerated data, Extrapolation method must be
Clip
.Because the fraction is
1
or0
, select Output selection > Index only.If you are using the index only output selection setting with the Interpolation Using Prelookup block, consider using the Number of sub-table selection dimensions parameter.
These are limitations for using enumerated data with this block:
The block does not support out-of-range input for enumerated data. When specifying enumerated data, include the entire enumeration set in the breakpoint data set. For example, use the
enumeration
function.When breakpoints data source is set to
Inport port
, the enumeration data type must have0
as the default value. For example, for this enumeration class, the default value ofGEAR1
must be0
.classdef(Enumeration) Gears < Simulink.IntEnumType enumeration GEAR1(1), GEAR2(2), GEAR3(4), GEAR4(8), SPORTS(16), REVERSE(32), NEUTRAL(0) end end
Dependencies
To enable this parameter, set the breakpoints data
Source to
Dialog
.
Note
When you set Source to Input
port
, the block inherits all breakpoint
attributes (data type, minimum, and maximum) from the
bp
input port.
Programmatic Use
Block Parameter:
BreakpointDataTypeStr |
Type: character vector |
Values:
'Inherit: Same as input' | 'Inherit: Inherit from
'Breakpoint data'' | 'double' | 'single' | 'int8' | 'uint8'
| 'int16' | 'uint16' | 'int32' | 'uint32' | 'int64' |
'uint64'| 'fixdt(1,16)' | 'fixdt(1,16,0)' |
'fixdt(1,16,2^0,0)'|'<data type
expression>' |
Default:
'Inherit: Same as input' |
Index — Index data type
uint32
(default) | int8
| uint8
| int16
| uint16
| int32
| uint32
| int64
| uint64
| fixdt(1,16)
| <data type expression>
Specify a data type that can index all elements in the breakpoint data set. You can:
Select a built-in integer data type from the list.
Specify an integer data type using a fixed-point representation.
The Data Type Assistant helps you set data attributes. To use the Data Type Assistant, click . For more information, see Specify Data Types Using Data Type Assistant.
Programmatic Use
Block Parameter:
IndexDataTypeStr |
Type: character vector |
Values:
'int8' | 'uint8' | 'int16' | 'uint16' | 'int32' |
'uint32' | 'int64' | 'uint64' | 'fixdt(1,16)' | '<data
type expression>' |
Default:
'uint32' |
Fraction — Fraction data type
Inherit: Inherit via internal
rule
(default) | double
| single
| fixdt(1,16,0)
| <data type expression>
Specify the data type of the interval fraction. You can:
Select a built-in data type from the list.
Specify data type inheritance through an internal rule.
Specify a fixed-point data type using the [Slope Bias] or binary-point-only scaling representation.
If you use the [Slope Bias] representation, the scaling must be trivial — that is, the slope is
1
and the bias is0
.If you use the binary-point-only representation, the fixed power-of-two exponent must be less than or equal to zero.
The Data Type Assistant helps you set data attributes. To use the Data Type Assistant, click . For more information, see Specify Data Types Using Data Type Assistant.
Dependencies
This parameter displays only when you set Output
selection on the Main
tab to Index and fraction
.
Programmatic Use
Block Parameter:
FractionDataTypeStr |
Type: character vector |
Values:
'Inherit: Inherit via internal rule' | 'double' |
'single' | 'fixdt(1,16,0)' | '<data type
expression>' |
Default:
'Inherit: Inherit via internal rule' |
Output — Output data type
Inherit: auto
(default) | bus: <object name>
To output a virtual bus, use the Inherit: auto
setting. The resulting virtual bus contains two elements, the index and
the fraction signals.
To output and specify a nonvirtual bus, use the Bus:
<object name>
template. Replace
<object name>
with the name of a
bus object that contains the index and fraction signals.
The bus object must contain two elements. The first element corresponds to the index signal and the second to the fraction signal.
The index and fraction bus element signals cannot be bus signals.
The data type and the complexity of the bus elements must meet the same constraints that apply to the index and fraction signals if you set Output selection to
Index and fraction
.
To create the bus object with the index and fraction bus elements, use MATLAB® code similar to this, customizing the bus object name and the names and data types of the bus elements.
% Bus object: kfBus elems(1) = Simulink.BusElement; elems(1).Name = 'Index'; elems(1).DataType = 'int8'; elems(2) = Simulink.BusElement; elems(2).Name = 'Fraction'; elems(2).DataType = 'double'; kfBus = Simulink.Bus; kfBus.Elements = elems; clear elems;
Alternatively, you can use the Type Editor to create or modify the bus object to use with the Prelookup block.
If you feed the bus output signal from this block to an Interpolation Using Prelookup block, select Require index and fraction as bus in that block.
Note
Use the Fixed-Point Tool data type override option to override bus objects with new bus objects that replace fixed-point data types with floating-point data types.
Overridden bus objects used with the Prelookup block can cause an error because the block does not accept floating-point data types for the first element in the bus.
If you encounter this issue, use the Fix
button to redefine the original bus object and protect it from being
overridden. For example, suppose you define the first element of the
bus object to be an int32
.
myBus.Elements(1).DataType
int32
Clicking the Fix button redefines the first bus element:
myBus.Elements(1).DataType = 'fixdt(''int32'',''DataTypeOverride'',''Off'')'
The Data Type Assistant helps you set data attributes. To use the Data Type Assistant, click . For more information, see Specify Data Types Using Data Type Assistant.
Dependencies
This parameter displays only when you set Output
selection on the Main
tab to Index and fraction as bus
.
Programmatic Use
Block Parameter:
OutputBusDataTypeStr |
Type: character vector |
Values:
'Inherit: auto' | 'Bus: <object name>' | '<data
type expression>' |
Default:
'Inherit: auto' |
Breakpoint Minimum — Minimum value breakpoint data can have
[]
(default) | scalar
Specify the minimum value that the breakpoint data can have. The
default value is []
(unspecified).
Dependencies
To enable this parameter, set the breakpoints data
Source to Dialog
on the Main tab.
Programmatic Use
Block Parameter:
BreakpointMin |
Type: character vector |
Value: scalar |
Default:
'[]' |
Breakpoint Maximum — Maximum value breakpoint data can have
[]
(default) | scalar
Specify the maximum value that the breakpoint data can have. The
default value is []
(unspecified).
Dependencies
To enable this parameter, set the breakpoints data
Source to Dialog
on the Main tab.
Programmatic Use
Block Parameter:
BreakpointMax |
Type: character vector |
Value: scalar |
Default:
'[]' |
Lock output data type setting against changes by the fixed-point tools — Option to prevent fixed-point tools from overriding Output data type
off
(default) | on
Select this parameter to prevent the fixed-point tools from overriding the Output data type you specify on the block. For more information, see Use Lock Output Data Type Setting (Fixed-Point Designer).
Programmatic Use
To set the block parameter value programmatically, use
the set_param
function.
Parameter: | LockScale |
Values: | 'off' (default) | 'on' |
Integer rounding mode — Rounding mode for fixed-point operations
Floor
(default) | Ceiling
| Convergent
| Nearest
| Round
| Simplest
| Zero
Specify the rounding mode for fixed-point operations. For more information, see Rounding Modes (Fixed-Point Designer).
Block parameters always round to the nearest representable value. To control the rounding of a block parameter, enter an expression using a MATLAB rounding function into the mask field.
Programmatic Use
To set the block parameter value programmatically, use
the set_param
function.
Parameter: | RndMeth |
Values: | 'Floor' (default) | 'Ceiling' | 'Convergent' | 'Nearest' | 'Round' | 'Simplest' | 'Zero' |
Block Characteristics
Data Types |
|
Direct Feedthrough |
|
Multidimensional Signals |
|
Variable-Size Signals |
|
Zero-Crossing Detection |
|
More About
Enumerated Values in Prelookup
Simulate a Prelookup block with enumerated values.
Suppose that you have a Prelookup block with an enumerated class like this defined:
classdef(Enumeration) Gears < Simulink.IntEnumType enumeration GEAR1(1), GEAR2(2), GEAR3(4), GEAR4(8), SPORTS(16), REVERSE(-1), NEUTRAL(0) end end
Prelookup block has these settings:
Breakpoints data value is
enumeration('Gears')
.Output selection is
Index only
.For an unordered search, set Index search method to
Linear search
and clear Begin index search using previous index result.Extrapolation method is
Clip
.
Interpolation using Prelookup block has these settings:
Number of dimensions to
1
.Table data value is
[5 10 20 40 80 -5 0]
.Interpolation method is
Flat
.Number of sub-table selection dimensions is
1
.
Simulation produces a vector [10 -5 80]
, which correspond to
GEAR2
, REVERSE
, and
SPORTS
.
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.
This block has one default HDL architecture.
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
|
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
|
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
|
Required Block Settings
Breakpoint data: For Source, select
Dialog
.Specification: You can select either
Explicit values
orEven spacing
.Index search method: Select
Evenly spaced points
.Extrapolation method: Select
Clip
.Diagnostic for out-of-range input: Select
Error
.Use last breakpoint for input at or above upper limit: Select this parameter.
Breakpoint: For Data Type, select
Inherit: Same as input
.Integer rounding mode: Select
Zero
,Floor
, orSimplest
.
Table Data Typing and Sizing
It is good practice to structure your table such that the spacing between breakpoints is a power of two. If the breakpoint spacing does not meet this condition, HDL Coder issues a warning. When the breakpoint spacing is a power of two, you can replace division operations in the prelookup step with right-shift operations.
All ports on the block require scalar values.
The coder permits floating-point data for breakpoints.
PLC Code Generation
Generate Structured Text code using Simulink® PLC Coder™.
Simulink PLC Coder has limited support for lookup table blocks. The coder does not support:
Number of dimensions greater than 2
Cubic spline interpolation method
Begin index search using a previous index mode
Cubic spline extrapolation method
Fixed-Point Conversion
Design and simulate fixed-point systems using Fixed-Point Designer™.
Version History
Introduced in R2006b
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