Re: Correlation matrix is not positive definite

Posted by viswa21 on Nov 29, 2011; 1:39am
URL: http://spssx-discussion.165.s1.nabble.com/Correlation-matrix-is-not-positive-definite-tp4999980p5030830.html

Hi Art,
             I am trying to find sets of profiles that are maximally similar with the set and maximally different between the sets.

All the bacteria were excited at single wavelength i.e. 225nm. Because visually we cant differentiate  the spectrum, so we are doing PCA to find out clusters of different bacteria at different places on PC1 Vs PC2.

To be more precise, I took emission spectra for four different kinds of bacteria.

For each bacteria i took 7 scans or repetitions with slight changes in their spectrum by changing physical parameter such as growth time. so there were 7*4=28 spectra. Now i applied data reduction steps. After clicking OK in factor analysis popup window. The correlation matrix shows it is not positive definite.

One of my colleague who had some idea tells me that, i need to carry F-test or power test to determine number of variables which represents spectrum rather having less number of variables. so plz advise me if there are any solutions like that exits??

Thanks

Regards
visu