Dear all,

I performed PCA in a set of 11 XANES spectra and I was trying to use some of the functions and tests developed by Malinowski to extract the number of primary components.

I found differences between eigenvalues calculated whit a matrix calculator and those calculated by ATHENA, but they are equivalent in some way since they explain the same amount of variance and when I calculate the IND function or  Malinowski F-test I reach the same conclusions.

To  calculate the eigenvalues with the matrix calculator I first normalized my data matrix (step height normalization) with ATHENA, then I export the data to an Excel spreadsheet where I centered them: z=(value-mean)/standard_dev. Then I used SVD and Eigenvalue decomposition to find the eigenvalues and those obtained with SVD explain exactly the same amount of variance than those found with ATHENA but they are different. In all the calculation I did, I used the same amount of points 161, points in each spectrum in ATHENA and in the matrix calculator, exactly the same energy interval.

I´d like to know if I am missing some step in the data pre-treatment that is prevented me to find the same eigenvalues obtained by ATHENA but also I´d like to know if I can straight forward use the values obtained with ATHENA to evaluate the functions proposed by Malinowski since these equations might be different depending if calculations are made using "covariance about the origin" or "correlation about the origin" and I am not sure what is the case.

Thanks in advance!

Best regards

Joselaine