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How to get cluster more than 2 if i have :

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Steven Pranata
Steven Pranata 2019 年 12 月 7 日
Commented: Image Analyst 2019 年 12 月 15 日
Y1 = mvnpdf(X,mu1,sigma1);
Y2 = mvnpdf(X,mu2,sigma2);
Y3 = mvnpdf(X,mu3,sigma3);
Cluster1 = Y1 > Y2;
Cluster2 = ~Cluster1;
Cluster3 = ??????

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Image Analyst
Image Analyst 2019 年 12 月 15 日
Original question
How to get cluster more than 2 if i have :
Y1 = mvnpdf(X,mu1,sigma1);
Y2 = mvnpdf(X,mu2,sigma2);
Y3 = mvnpdf(X,mu3,sigma3);
Cluster1 = Y1 > Y2;
Cluster2 = ~Cluster1;
Cluster3 = ??????

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件の回答 (2)

Walter Roberson
Walter Roberson 2019 年 12 月 7 日
Cluster1 = Y1 > Y2 & Y1 > Y3 & Y2 > Y3
Cluster2 = Y1 > Y2 & Y1 > Y3 & Y2 <= Y3
Cluster3 = Y1 > Y2 & Y1 <= Y3 %Y2 < Y3 by transitive
Cluster4 = Y1 <= Y2 & Y1 > Y3 %Y2 > Y3 by transitive
Cluster5 = Y1 <= Y2 & Y1 <= Y3 & Y2 > Y3
Cluster6 = Y1 <= Y2 & Y1 <= Y3 & Y2 <= Y3
Or use kmeans() with the number of clusters that you want.
Caution: kmeans will always return the number of clusters you ask for, even if it does not make sense for the data.

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Steven Pranata
Steven Pranata 2019 年 12 月 7 日
If i just want 3 clusters? Its same?
Walter Roberson
Walter Roberson 2019 年 12 月 7 日
Pick any three of those.
Note that there is a difference between finding three clusters, versus finding three meaningfull clusters.
If your mu* values are well separated, you could probably use the mu* values as the locations around which clusters would be expected to form. If you were to sort the mu values, ms1, ms2, ms3, then you could form clusters "value <= (ms1+ms2)/2, (ms1+ms2)/2 <= value < (ms2+ms3)/2, value >= (ms2+ms3)/2 . These would, however, not necessarily represent equal areas.
Walter Roberson
Walter Roberson 2019 年 12 月 7 日
I doubt that you want to be comparing Y1 to Y2 or Y3. I think you want to be throwing all of the values into one basket, [Y1, Y2, Y3] and then trying to form clusters that can distinguish which of the three sources the values came from.

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Image Analyst
Image Analyst 2019 年 12 月 7 日
Just define Cluster3 to be something. What would you want it to be? It could be virtually anything you direct it to be.

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