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I am having a problem in Matlab. I would like to use kmeans clustering and then get the value and index of the centroid. For example, if there is an $5*5$ array, we do kmeans clustering where k=2 and we get 2 centroids. How can I get these values for these centroids? I am currently working depth in matlab and would like to implement a research paper for this.

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  • $\begingroup$ i already used ke k-means fuction , build-in in maltab, doesnt give me those indexes $\endgroup$ – arslan ahmed Jan 31 '20 at 18:50
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    $\begingroup$ Try and gather a better understanding of the algorithm. It is quite an easy to understand procedure. en.wikipedia.org/wiki/K-means_clustering Also, please check your punctuation, it is hard to understand your question. $\endgroup$ – VincFort Jan 31 '20 at 19:17
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From the document: https://www.mathworks.com/help/stats/kmeans.html

idx = kmeans(X,k)
idx = kmeans(X,k,Name,Value)
[idx,C] = kmeans(___)
[idx,C,sumd] = kmeans(___)
[idx,C,sumd,D] = kmeans(___)

idx = kmeans(X,k) performs k-means clustering to partition the observations of the n-by-p data matrix X into k clusters, and returns an n-by-1 vector (idx) containing cluster indices of each observation. Rows of X correspond to points and columns correspond to variables.

By default, kmeans uses the squared Euclidean distance metric and the k-means++ algorithm for cluster center initialization.

[idx,C] = kmeans(___) returns the k cluster centroid locations in the k-by-p matrix C.

The code is:

[idx,C] = kmeans(X,3);
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  • $\begingroup$ i used this matlab fuction , in this function 2 things are returned , idx and C , idx tell us about which value belong to which clusterr i.e 1st one to 1st cluster etc and C is k-by-p matrix having centroid , where k is the number of cluster u want and p is ? sorry i am new to this , what i am trying to do is to give him a big array like 1024*768 and the call this kmeans function , but when the result come it will give 2*768 array of C centorid, as mention kmeans(X,k) performs k-means clustering to partition the observations of the n-by-p data matrix X into k clusters, i only want 2 values $\endgroup$ – arslan ahmed Feb 1 '20 at 15:04
  • $\begingroup$ p is the feature dimension, the column number, so it is 768 in your case. n is observation number, the row number. So you have n=1024 and p=768. You didn't get two values, you get two vectors (don't mistake this), and each has 768 dimensions. The centroid is not value it is the "coordinate". $\endgroup$ – Bill Chen Feb 1 '20 at 19:17

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