Prelookup
Calculates the number and fraction of the interval for interpolation.
blockType: PreLookup
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Path in the library: |
Description
Block Prelookup calculates the number and fraction for the interval, which determine how its input value is correlates with a set of reference points.
Block Prelookup works best with a block Interpolation Using Prelookup. Submit the received number and fraction values to the block Interpolation Using Prelookup for interpolation - dimensional table. These two blocks have distributed algorithms. When combined together, they perform the same operation as the integrated algorithm in the block n-D Lookup Table. However, the blocks Prelookup and Interpolation Using Prelookup provide more flexibility and more efficient modeling and code generation than a block n-D Lookup Table.
Supported operations with blocks
To use the block Prelookup, a set of anchor point values must be specified. In this case, you can choose whether to specify the values of the reference points directly in the dialog box or transfer them via the bp input port by setting the parameter Source value Dialog or Input port.
Typically, a data set of reference points corresponds to one dimension of tabular data in a block Interpolation Using Prelookup.
Block Prelookup generates a pair of outputs for each input value by calculating:
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reference point numbers whose value is less than or equal to and forms an interval containing .
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fractions of an interval (fraction) in the range representing the normalized position on the interval between the reference point with the found number and the next reference point.
The number is counted from zero or from one, depending on the value of the parameter Indexing Mode:
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Zero-based indexing— indexing of reference points starts with0'. Example: if the set of reference points is `[0 5 10 20 50 100]and the input value If the interval is equal to55, then the number is equal to4, and the interval fraction is `0.1'. -
One-based indexing— indexing of reference points starts with1'. Example: if the set of reference points is `[0 5 10 20 50 100]and the input value If the interval is equal to55, then the number is equal to5, and the fraction of the interval is `0.1'.
The interval fraction may be negative or greater than 1 if the input signal is out of range.
Ports
Input
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u
—
input signal u
vector
Details
Block Prelookup accepts signals with real values of any numeric data type supported by Engee except Bool.
| Data types |
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| Complex numbers support |
No |
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u
—
input signal u
scalar | vector | matrix
Details
Block Prelookup accepts signals with real values of any numeric data type supported by Engee except Bool.
| Data types |
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| Complex numbers support |
No |
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bp
—
reference points
vector
Details
Block Prelookup accepts as reference points signals with real values of any numeric data type supported by Engee except Bool.
Dependencies
To use this port, set parameter Source value Input port.
| Data types |
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| Complex numbers support |
No |
Output
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k
—
number of the interval containing the input signal u
scalar | vector | matrix
Details
The number is a real integer defining the interval containing the input signal .
The number counts from zero or from one depending on the value of the parameters Indexing Mode.
| Data types |
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| Complex numbers support |
No |
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f
—
fraction representing the normalised position of the input in the interval
scalar | vector | matrix
Details
The fraction represents the normalised position of the input in the interval .
| Data types |
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| Complex numbers support |
No |
Parameters
Breakpoints data
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Source —
source of values for the reference points
Dialog | Input port
Details
Source of values for the datums:
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Dialog- The reference point values are specified in the Value parameters. -
Input port- The reference point values will be obtained via the corresponding input point.
| Values |
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| Default value |
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| Program usage name |
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| Tunable |
No |
| Evaluatable |
No |
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Value —
datums
Array of real numbers
Details
Reference points. The set of anchor points must be a strictly monotonically increasing vector containing two or more elements.
Dependencies
To use this parameter, set the parameters to Source value Dialog.
| Default value |
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| Program usage name |
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| Tunable |
Yes |
| Evaluatable |
Yes |
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Indexing Mode —
number value reference method
Zero-based indexing | One-based indexing
Details
The number value is counted from zero if the value is set to Zero-based indexing, or from one if the value is set One-based indexing.
| Values |
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| Default value |
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| Program usage name |
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| Tunable |
No |
| Evaluatable |
No |
Algorithm
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Output selection —
output signals
Index and fraction | Index only
Details
Options for selection:
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Index only- outputs only the number, no share. -
Index and fraction- Outputs the number and fraction as separate signals.
| Values |
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| Default value |
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| Program usage name |
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| Tunable |
No |
| Evaluatable |
No |
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Index search method —
interval number search method
Evenly spaced points | Linear search | Binary search
Details
Each search method has speed advantages in different situations:
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For evenly spaced anchor points (e.g., 10, 20, 30, and so on), optimal speed is achieved by choosing
Evenly spaced pointstable numbers for the calculation. This algorithm uses only the first two anchor points of the set to determine the offset and distance between the remaining points. -
For non-uniformly distributed landmark points, it is recommended:
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Linear search- if the input values for do not change much between counting steps. -
Binary search- if the input values for change by more than one or two table intervals per count step.
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A suboptimal choice of number lookup method can lead to poor performance of models that rely heavily on lookup tables.
| Values |
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| Default value |
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| Program usage name |
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| Tunable |
No |
| Evaluatable |
No |
#
Extrapolation method —
method of processing input values that are out of range
Clip | Linear
Details
The method used by the block to extrapolate values for all inputs outside the range of the dataset of reference points.
Read more about extrapolation methods here: Methods for approximating function values
| Values |
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| Default value |
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| Program usage name |
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| Tunable |
No |
| Evaluatable |
No |