what is the 'NSMethod','exhaustive' k-nearest neighbor classifier

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I am using the k-nearest neighbor classifier as the below code.
Could you explain what 'NSMethod','exhaustive' are?
Is it related to distance metric learning? (It learns a metric that pulls the neighbor candidates near, while pushes near data from different classes out of the target neighbors margin.) I got a high accuracy than I expected.
clear all
close all
for i = 2:30:750
X = csvread('kth_optical_only.csv');
Y = csvread('kth_optical_only_class1.csv');
X = X(:,1:i);
Mdl = fitcknn(X,Y,'NumNeighbors',3,...
rng(1); % For reproducibility
CVKNNMdl = crossval(Mdl, 'KFold', 5);
classAccuracy(i) = 100 - kfoldLoss(CVKNNMdl, 'LossFun', 'ClassifError')*100;

Accepted Answer

Divya Gaddipati
Divya Gaddipati on 13 Apr 2020
NSMethod is the Nearest neighbor search method, specified as either 'kdtree' or 'exhaustive'.
  • 'kdtree' — Creates and uses a Kd-tree to find nearest neighbors.
  • 'exhaustive' — Uses the exhaustive search algorithm. When predicting the class of a new point xnew, the algorithm computes the distance values from all points in X to xnew to find nearest neighbors.
For information on exhaustive and kdtree based searching, you can refer to the following links:
Hope this helps!

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