[ROOT] Incorrect mean and sigma calculation in TPrincipal?
From: Suyong Choi (suyong@fnal.gov)
Date: Sat Oct 13 2001 - 23:58:25 MEST
Hi,
It seems like the first data input is discarded and the sigma
isn't right either. I'm using v3.01 on IRIX 6.5
root [0] TPrincipal pca1(2,"");
root [1] Double_t *data=new Double_t[2];
root [2] data[0]=10.0;data[1]=10.0;
root [3] pca1.AddRow(data);
root [4] pca1.Print();
Variable # | Mean Value | Sigma | Eigenvalue
-------------+------------+------------+------------
1 | 10 | 0 | 0
2 | 10 | 0 | 0
root [5] data[0]=5.0;data[1]=5.0;
root [6] pca1.AddRow(data);
root [7] pca1.Print();
Variable # | Mean Value | Sigma | Eigenvalue
-------------+------------+------------+------------
1 | 5 | 0 | 0
2 | 5 | 0 | 0
root [8] data[0]=0.0;data[1]=0.0;
root [9] pca1.AddRow(data);
root [10] pca1.Print();
Variable # | Mean Value | Sigma | Eigenvalue
-------------+------------+------------+------------
1 | 2.5 | 0 | 0
2 | 2.5 | 0 | 0
root [11] pca1.MakePrincipals()
root [12] pca1.Print();
Variable # | Mean Value | Sigma | Eigenvalue
-------------+------------+------------+------------
1 | 2.5 | 1.768 | 1
2 | 2.5 | 1.768 | 1.11e-16
Regards,
Suyong
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: Tue Jan 01 2002 - 17:51:02 MET