KNN Search
Libraries:
Statistics and Machine Learning Toolbox /
Neighborhood Searcher
Description
The KNN Search block finds the nearest neighbors in the data to a query
point using a nearest neighbor searcher object (ExhaustiveSearcher
or KDTreeSearcher
).
Import a trained searcher object containing observation data into the block by specifying the name of a workspace variable that contains the object. The input port x receives a query point, and the output port Idx returns the indices of the knearest neighbor points in the data. The optional output port D returns the distances between the query point and the nearest neighbor points.
Examples
Find Nearest Neighbors Using KNN Search Block
Train a nearest neighbor searcher model, and then use the KNN Search block for label prediction.
 Since R2023b
 Open Live Script
Ports
Input
x — Query point
row vector
Query point, specified as a row vector. x must have the same
number of columns as the number of predictor variables in the
searcher
object specified by Select nearest
neighbor searcher. The columns of x must be in
the same order as those in the searcher
object.
Data Types: single
 double
 half
 int8
 int16
 int32
 int64
 uint8
 uint16
 uint32
 uint64
 Boolean
 fixed point
Output
Idx — Indices of nearest neighbors
numeric row vector  1by1 cell array
Indices of the nearest neighbors in the data, returned as a numeric row vector or 1by1 cell array.
If you do not select Include ties on the Main tab of the Block Parameters dialog box, then the block returns a 1byk numeric row vector, where k is the number of nearest neighbors searched. Each column of the row vector contains the index of a nearest neighbor point in the data, ordered by increasing distance to the query point x.
If you select Include ties on the Main tab of the Block Parameters dialog box, then the block returns a 1by1 cell array as a variablesize signal containing a numeric row vector of at least k indices of the closest observations in the data to the query point x. The columns of the vector are ordered by increasing distance to the query point.
Data Types: single
 double
 half
 int8
 int16
 int32
 int64
 uint8
 uint16
 uint32
 uint64
 fixed point
D — Distances of nearest neighbors
numeric row vector  1by1 cell array
Distances of the nearest neighbors to the query points, returned as a numeric row vector or 1by1 cell array.
If you do not select Include ties on the Main tab of the Block Parameters dialog box, then the block returns a 1byk numeric row vector, where k is the number of nearest neighbors searched. Each column of the row vector contains the distance of a nearest neighbor point in the data to the query point x, according to the distance metric. The columns of the row vector are ordered by increasing distance to the query point.
If you select Include ties on the Main tab of the Block Parameters dialog box, then the block returns a 1by1 cell array as a variablesize signal containing a numeric row vector of at least k distances of the closest observations in the data to the query point x. The columns of the vector are ordered by increasing distance to the query point.
Dependencies
To enable this port, select Add output port for nearest neighbor distances in the KNN Search block.
Data Types: single
 double
 half
 int8
 int16
 int32
 int64
 uint8
 uint16
 uint32
 uint64
 fixed point
Parameters
Main
Select nearest neighbor searcher — Nearest neighbor search method
searcher
(default)  ExhaustiveSearcher
object  KDTreeSearcher
object
Specify the name of a workspace variable that contains an ExhaustiveSearcher
or KDTreeSearcher
object.
Note
The software uses the default settings for all parameters that you can specify in the Block Parameters dialog box. The parameters in the dialog box override those of the searcher object.
Programmatic Use
Block Parameter:
NeighborhoodSearcher 
Type: workspace variable 
Values:
ExhaustiveSearcher object  KDTreeSearcher
object 
Default:
"searcher" 
Add output port for nearest neighbor distances — Add second output port for nearest neighbor distances
off
(default)  on
Select the check box to include the second outport port D in the KNN Search block.
Programmatic Use
Block Parameter:
ShowOutputDistances 
Type: character vector 
Values:
"off"  "on" 
Default:
"off" 
Number of nearest neighbors — Number of nearest neighbors
1
(default)  positive integer
Specify the number of nearest neighbors to find in the data for the query point.
Programmatic Use
Block Parameter:
NumNeighbors 
Type: positive integer 
Values:
single  double 
Default:
1 
Include ties — Flag to include all nearest neighbors
off
(default)  on
If you do not select Include ties on the Main tab of the Block Parameters dialog box, then the block selects the observation with the smallest index among the observations that have the same distance from the query point.
If you select Include ties:
The block output includes all nearest neighbors whose distances are equal to the kth smallest distance in the output arguments. If more than five nearest neighbors have equal distance to the kth smallest distance, the block output includes only the first five nearest neighbors with the smallest index values.
The Idx and D block outputs are 1by1 cell arrays where each cell contains a vector of at least k indices and distances, respectively. The columns in the vectors are ordered by increasing distance to the query point.
Programmatic Use
Block Parameter:
IncludeTies 
Type: character vector 
Values:
"off"  "on" 
Default:
"off" 
Distance metric — Distance metric
euclidean
(default)  chebychev
 cityblock
 minkowski
 correlation
 cosine
 hamming
 jaccard
 mahalanobis
 seuclidean
 spearman
Specify the distance metric used to find nearest neighbors in the data to the query point.
For both ExhaustiveSearcher
and KDTreeSearcher
objects, the block supports these distance metrics.
Value  Description 

"chebychev"  Chebychev distance (maximum coordinate difference) 
"cityblock"  City block distance 
"euclidean"  Euclidean distance 
"minkowski"  Minkowski distance. The default exponent is 2. You can specify a different exponent in the Block Parameters dialog box. 
For an ExhaustiveSearcher
object, the block also supports these
distance metrics.
Value  Description 

"correlation"  One minus the sample linear correlation between observations (treated as sequences of values) 
"cosine"  One minus the cosine of the included angle between observations (treated as row vectors) 
"hamming"  Hamming distance, which is the percentage of coordinates that differ 
"jaccard"  One minus the Jaccard coefficient, which is the percentage of nonzero coordinates that differ 
"mahalanobis"  Mahalanobis distance, computed using a positive definite covariance
matrix. The block computes the covariance matrix from the data in the
searcher object, by default. You can specify a customized
covariance matrix in the Block Parameters dialog box. 
"seuclidean"  Standardized Euclidean distance. Each coordinate difference between the query point x and the data is scaled by dividing by the corresponding element of the standard deviation computed from the data. You can specify a different scaling method in the Block Parameters dialog box. 
"spearman"  One minus the sample Spearman's rank correlation between observations (treated as sequences of values) 
Note
The distance metric setting overrides the
Distance
property of the specifiedsearcher
object.The KNN Search block does not support the
"fasteuclidean"
or"fastseuclidean"
distance metric (see Distance Metrics).
Programmatic Use
Block Parameter:
DistanceMetric 
Type: character vector 
Values:
"euclidean"  "chebychev"  "cityblock"  "minkowski"  "correlation" 
"cosine"  "hamming"  "jaccard"  "mahalanobis"  "seuclidean" 
"spearman" 
Default:
"euclidean" 
Covariance matrix — Covariance matrix for Mahalanobis distance metric
Computed using data in searcher
(default)  Customized
The block computes the covariance matrix from the data in the
searcher
object, by default. You can specify a customized
covariance matrix by selecting Customized
and entering a positive
definite matrix in the Customized matrix
box.
Note
This setting overrides the DistParameter
property of the
specified searcher
object.
Programmatic Use
Block Parameter:
CovarianceMatrix 
Type: positive definite matrix 
Values:
"Computed using data in searcher" 
"Customized" 
Default:
"Computed using data in searcher" 
Dependencies
To enable this parameter, set Distance Metric to
"mahalanobis"
.
Scale — Scale parameter value for standardized Euclidean distance metric
Standard deviation of data in
searcher
(default)  Customized
The block computes the scale parameter value from the data in the
searcher
object, by default. You can specify a customized scale
parameter value by selecting Customized
and entering a nonnegative
numeric row vector in the Customized scale
text box. The row vector
must have the same number of columns as the number of predictor variables in the
searcher
object. When the block computes the standardized
Euclidean distance, each coordinate of the data is scaled by the corresponding element
of Scale
, as is the query point.
Note
This setting overrides the DistParameter
property of the
specified searcher
object.
Programmatic Use
Block Parameter:
Scale 
Type: nonnegative numeric row vector 
Values:
"Standard deviation of data in searcher" 
"Customized" 
Default:
"Standard deviation of data in searcher" 
Dependencies
To enable this parameter, set Distance Metric to
"seuclidean"
.
P — Exponent for Minkowski distance metric
2
(default)  positive integer
Specify the exponent for the Minkowski distance metric. For the default case of P = 2, the Minkowski distance gives the Euclidean distance. For the special case of P = 1, the Minkowski distance gives the city block distance. For the special case of P = ∞, the Minkowski distance gives the Chebychev distance.
Note
This setting overrides the DistParameter
property of the
specified searcher
object.
Programmatic Use
Block Parameter:
MinkExp 
Type: positive integer 
Values:
positive integer 
Default:
2 
Dependencies
To enable this parameter, set Distance Metric to
"minkowski"
.
Data Types
FixedPoint Operational ParametersInteger rounding mode — Rounding mode for fixedpoint operations
Floor
(default)  Ceiling
 Convergent
 Nearest
 Round
 Simplest
 Zero
Specify the rounding mode for fixedpoint operations. For more information, see Rounding Modes (FixedPoint Designer).
Block parameters always round to the nearest representable value. To control the rounding of a block parameter, enter an expression into the mask field using a MATLAB^{®} rounding function.
Programmatic Use
Block Parameter:
RndMeth 
Type: character vector 
Values:
"Ceiling"  "Convergent"  "Floor"  "Nearest"  "Round"  "Simplest" 
"Zero" 
Default:
"Floor" 
Saturate on integer overflow — Method of overflow action
off
(default)  on
Specify whether overflows saturate or wrap.
Action  Rationale  Impact on Overflows  Example 

Select this check box
(  Your model has possible overflow, and you want explicit saturation protection in the generated code.  Overflows saturate to either the minimum or maximum value that the data type can represent.  The maximum value that the 
Clear this check box
(  You want to optimize the efficiency of your generated code. You want to avoid overspecifying how a block handles outofrange signals. For more information, see Troubleshoot Signal Range Errors (Simulink).  Overflows wrap to the appropriate value that the data type can represent.  The maximum value that the 
Programmatic Use
Block Parameter:
SaturateOnIntegerOverflow 
Type: character vector 
Values:
"off"  "on" 
Default:
"off" 
Lock output data type setting against changes by the fixedpoint tools — Prevention of fixedpoint tools from overriding data type
off
(default)  on
Select this parameter to prevent the fixedpoint tools from overriding the data type you specify for the block. For more information, see Use Lock Output Data Type Setting (FixedPoint Designer).
Programmatic Use
Block Parameter:
LockScale 
Type: character vector 
Values:
"off"  "on" 
Default:
"off" 
Index data type — Data type of index output
Inherit: auto
(default)  double
 single
 half
 int8
 uint8
 int16
 uint16
 int32
 uint32
 int64
 uint64
 fixdt(1,16,0)
 fixdt(1,16,2^0,0)
 <data type expression>
Specify the data type for the Idx output. The type can be
inherited, specified directly, or expressed as a data type object such as
Simulink.NumericType
.
Click the Show data type assistant button to display the Data Type Assistant, which helps you set the data type attributes. For more information, see Specify Data Types Using Data Type Assistant (Simulink).
Programmatic Use
Block Parameter:
IndicesDataTypeStr 
Type: character vector 
Values: "Inherit: auto"
 "double"  "single" 
"half"  "int8" 
"uint8"  "int16" 
"uint16"  "int32" 
"uint32"  "int64" 
"uint64"  "fixdt(1,16,0)" 
"fixdt(1,16,2^0,0)"  "<data type
expression>" 
Default: "Inherit:
auto" 
Index data type Minimum — Minimum of index output
[]
(default)  scalar
Specify the minimum value of the Idx output range that Simulink^{®} checks.
Simulink uses the minimum value to perform:
Parameter range checking for some blocks (see Specify Minimum and Maximum Values for Block Parameters (Simulink)).
Simulation range checking (see Specify Signal Ranges (Simulink) and Enable Simulation Range Checking (Simulink)).
Optimization of the code that you generate from the model. This optimization can remove algorithmic code and affect the results of some simulation modes, such as softwareintheloop (SIL) mode or external mode. For more information, see Optimize using the specified minimum and maximum values (Embedded Coder).
Note
The Index data type Minimum parameter does not saturate or clip the actual Idx output signal. To do so, use the Saturation (Simulink) block instead.
Programmatic Use
Block Parameter:
IndicesOutMin 
Type: scalar 
Values: "[]"  scalar 
Default: "[]" 
Index data type Maximum — Maximum of index output
[]
(default)  scalar
Specify the maximum value of the Idx output range that Simulink checks.
Simulink uses the maximum value to perform:
Parameter range checking for some blocks (see Specify Minimum and Maximum Values for Block Parameters (Simulink)).
Simulation range checking (see Specify Signal Ranges (Simulink) and Enable Simulation Range Checking (Simulink)).
Optimization of the code that you generate from the model. This optimization can remove algorithmic code and affect the results of some simulation modes, such as softwareintheloop (SIL) mode or external mode. For more information, see Optimize using the specified minimum and maximum values (Embedded Coder).
Note
The Index data type Maximum parameter does not saturate or clip the actual Idx output signal. To do so, use the Saturation (Simulink) block instead.
Programmatic Use
Block Parameter:
IndicesOutMax 
Type: scalar 
Values: "[]"  scalar 
Default: "[]" 
Distance data type — Data type of distance output
Inherit: auto
(default)  double
 single
 half
 int8
 uint8
 int16
 uint16
 int32
 uint32
 int64
 uint64
 fixdt(1,16,0)
 fixdt(1,16,2^0,0)
 <data type expression>
Specify the data type for the distance (D) output. The type
can be inherited, specified directly, or expressed as a data type object such as
Simulink.NumericType
.
Click the Show data type assistant button to display the Data Type Assistant, which helps you set the data type attributes. For more information, see Specify Data Types Using Data Type Assistant (Simulink).
Programmatic Use
Block Parameter:
DistanceDataTypeStr 
Type: character vector 
Values: "Inherit: auto"
 "double"  "single" 
"half"  "int8" 
"uint8"  "int16" 
"uint16"  "int32" 
"uint32"  "int64" 
"uint64"  "fixdt(1,16,0)" 
"fixdt(1,16,2^0,0)"  "<data type
expression>" 
Default: "Inherit:
auto" 
Note
Fixedpoint data types are not supported for the Spearman distance metric.
Dependencies
To enable this parameter, select Add output port for nearest neighbor distances on the Main tab of the Block Parameters dialog box.
Distance data type Minimum — Minimum of distance output
[]
(default)  scalar
Specify the minimum value of the distance (D) output range that Simulink checks.
Simulink uses the minimum value to perform:
Parameter range checking for some blocks (see Specify Minimum and Maximum Values for Block Parameters (Simulink)).
Simulation range checking (see Specify Signal Ranges (Simulink) and Enable Simulation Range Checking (Simulink)).
Optimization of the code that you generate from the model. This optimization can remove algorithmic code and affect the results of some simulation modes, such as softwareintheloop (SIL) mode or external mode. For more information, see Optimize using the specified minimum and maximum values (Embedded Coder).
Note
The Distance data type Maximum parameter does not saturate or clip the actual D output signal. To do so, use the Saturation (Simulink) block instead.
Programmatic Use
Block Parameter:
DistanceOutMin 
Type: scalar 
Values: "[]"  scalar 
Default: "[]" 
Dependencies
To enable this parameter, select Add output port for nearest neighbor distances on the Main tab of the Block Parameters dialog box.
Distance data type Maximum — Maximum of distance output
[]
(default)  scalar
Specify the maximum value of the distance (D) output range that Simulink checks.
Simulink uses the maximum value to perform:
Parameter range checking for some blocks (see Specify Minimum and Maximum Values for Block Parameters (Simulink)).
Simulation range checking (see Specify Signal Ranges (Simulink) and Enable Simulation Range Checking (Simulink)).
Optimization of the code that you generate from the model. This optimization can remove algorithmic code and affect the results of some simulation modes, such as softwareintheloop (SIL) mode or external mode. For more information, see Optimize using the specified minimum and maximum values (Embedded Coder).
Note
The Distance data type Maximum parameter does not saturate or clip the actual D output signal. To do so, use the Saturation (Simulink) block instead.
Programmatic Use
Block Parameter:
DistanceOutMax 
Type: scalar 
Values: "[]"  scalar 
Default: "[]" 
Dependencies
To enable this parameter, select Add output port for nearest neighbor distances on the Main tab of the Block Parameters dialog box.
Block Characteristics
Data Types 

Direct Feedthrough 

Multidimensional Signals 

VariableSize Signals 

ZeroCrossing Detection 

Alternative Functionality
You can use a MATLAB Function block with the knnsearch
object function of a nearest neighbor searcher object (ExhaustiveSearcher
or KDTreeSearcher
). For an example, see Predict Class Labels Using MATLAB Function Block.
When deciding whether to use the KNN Search block in the Statistics and Machine Learning Toolbox™ library or a MATLAB Function block with the knnsearch
function, consider the following:
If you use the Statistics and Machine Learning Toolbox library block, you can use the FixedPoint Tool (FixedPoint Designer) to convert a floatingpoint model to fixed point.
Support for variablesize arrays must be enabled for a MATLAB Function block with the
knnsearch
function.
Extended Capabilities
C/C++ Code Generation
Generate C and C++ code using Simulink® Coder™.
FixedPoint Conversion
Design and simulate fixedpoint systems using FixedPoint Designer™.
Version History
Introduced in R2023b
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